Ace844

Hello Everyone, Here's a great albeit older paper which describes the MOA of Vasopressin. HTH, ACE844 [web:b6ac9a5814]http://arjournals.annualreviews.org/doi/pdf/10.1146/annurev.me.37.020186.000305[/web:b6ac9a5814]

[marq=left:288ec6524b]WARNING, WARNING:::[/marq:288ec6524b] : "FL_Medic," Sweet, thanks for the compliment and the info. I will definately keep your system in mind. That being said, what would you say if I told you I am not a medic and just a lowly basic?!?!.... 8) :shock: ACE [marq=left:288ec6524b]WARNING, WARNING:::[/marq:288ec6524b] :

Here's something which seems like it will be an emerging therepy- assessment device..You can read alot more about it here: Cardiac vs Pulmonary Dyspnea - New tool to assess COPD/CHF and here's a post whith the same discussion essentially just in a different area of the forums:: Cardiac vs Pulmonary Dyspnea - New tool to assess COPD/CHF Out Here, ACE844

[marq=left:c89f1d8764]WARNING, WARNING:::[/marq:c89f1d8764] : I considered things down your way, but the pay sucked..then there was the whole major hurricane thing..but I guess the juries still out :wink: I'm glad you've gotten some good people form here. Like everywhere we have more than our fair share of meatballs. OOC, you guys seem to have a huge turn over and are always hiring...why? Thanks, ACE844 :

Here are some studies for you to peruse, I have not had the benefit of using pre-hospital thrombolysis. They did a 2 year study here, on this and it's use in conjunction with 2b/3a inhibitors as well; and then OEMS never follwed it up or released its use to the 'street'. http://www.clinicalcardiology.org/productc...S4/CC22S410.pdf 1. Morrison LJ et al. Mortality and prehospital thrombolysis for acute myocardial infarction: a meta-analysis. JAMA 2000; 283: 2686–2692. Abstract 2. Weaver WK et al. Prehospital-initiated vs hospital-initiated thrombolytic therapy. The Myocardial Infarction Triage and Intervention (MITI) Trial. JAMA 1993; 270:1211–1216. Abstract 3. Roth A et al. Should thrombolytic therapy be administered in the mobile intensive care unit in patients with evolving myocardial infarction? A pilot study. J Am Coll Cardiol 1990; 15: 932–936. Abstract 4. GREAT group. Feasibility, safety, and efficacy of domiciliary thrombolysis by general practitioners. BMJ 1992; 305: 548–553. Abstract 5. Castaigne AD et al. Prehospital use of APSAC: results of placebo-controlled study. Am J Cardiol 1989; 64: 30A–33A. Abstract 6. European Myocardial Infarction Project Group. Prehospital thrombolytic therapy in patients with suspected acute myocardial-infarction. EMIP trial. N Engl J Med 1993; 329: 383–389. Abstract 7. Schofer J et al. Prehospital thrombolysis in acute myocardial infarction. Am J Cardiol 1990; 66: 1429–1433. Abstract 8. Boersma E et al. Early thrombolytic treatment in acute myocardial infarction: reappraisal of the golden hour. Lancet 1996, 348:771–775. 9. Vermeulen M, Burgess R, Graham A. EMS Database Statistical Report. Toronto: Toronto Emergency Medical Services and Sunnybrook Base Hospital, 2000:1–22. 10. Morrison LJ et al. Mortality and thrombolysis time intervals with prehospital 12-lead electrocardiogram and advance emergency department notification: a meta-analysis. Acad Emergency Med 2000; 7: 479. 11. Canto JG et al. The prehospital electrocardiogram in acute myocardial infarction: is its full potential being realized? J Am Coll Cardiol 1997; 29: 498–505. Abstract 12. Rawles J. Myocardial salvage with early anistreplase treatment. Clin Cardiol 1997; 20: 6–10. Abstract Prehospital administration of reteplase may accelerate reperfusion in ST-elevation myocardial infarction Laurie J. Morrison MD, MSC, FRCPC Division of Pre-Hospital Care, Sunnybrook and Women’s, Ontario Air Ambulance and Toronto Land Ambulance, Base Hospital Programs, Toronto Emergency Medical Services, Department of Medicine, University of Toronto, Canada, USA TI - Evaluation of the time saved by prehospital initiation of reteplase for ST-elevation myocardial infarction: results of The Early Retavase-Thrombolysis in Myocardial Infarction (ER-TIMI) 19 trial. AU - Morrow DA; Antman EM; Sayah A; Schuhwerk KC; Giugliano RP; deLemos JA; Waller M; Cohen SA; Rosenberg DG; Cutler SS; McCabe CH; Walls RM; Braunwald E SO - J Am Coll Cardiol 2002 Jul 3;40(1):71-7. TI - Impact of prehospital thrombolysis for acute myocardial infarction on 1-year outcome: results from the French Nationwide USIC 2000 Registry. AU - Danchin N; Blanchard D; Steg PG; Sauval P; Hanania G; Goldstein P; Cambou JP; Gueret P; Vaur L; Boutalbi Y; Genes N; Lablanche JM SO - Circulation 2004 Oct 5;110(14):1909-15. Epub 2004 Sep 27. TI - Trends in prehospital delay time and use of emergency medical services for acute myocardial infarction: experience in 4 US communities from 1987-2000. AU - McGinn AP; Rosamond WD; Goff DC Jr; Taylor HA; Miles JS; Chambless L SO - Am Heart J 2005 Sep;150(3):392-400. Prehospital delay in patients hospitalized with heart attack symptoms in the United States: the REACT trial. Rapid Early Action for Coronary Treatment (REACT) Study Group. AU - Goff DC Jr; Feldman HA; McGovern PG; Goldberg RJ; Simons-Morton DG; Cornell CE; Osganian SK; Cooper LS; Hedges JR SO - Am Heart J 1999 Dec;138(6 Pt 1):1046-57. Prehospital thrombolysis: beneficial effects of very early treatment on infarct size and left ventricular function. AU - Linderer T; Schroder R; Arntz R; Heineking ML; Wunderlich W; Kohl K; Forycki F; Henzgen R; Wagner J SO - J Am Coll Cardiol 1993 Nov 1;22(5):1304-10 Mortality and prehospital thrombolysis for acute myocardial infarction: A meta-analysis. AU - Morrison LJ; Verbeek PR; McDonald AC; Sawadsky BV; Cook DJ SO - JAMA 2000 May 24-31;283(20):2686-92. Prehospital thrombolytic therapy in patients with suspected acute myocardial infarction. The European Myocardial Infarction Project Group. SO - N Engl J Med 1993 Aug 5;329(6):383-9. Prehospital-initiated vs hospital-initiated thrombolytic therapy. The Myocardial Infarction Triage and Intervention Trial. AU - Weaver WD; Cerqueira M; Hallstrom AP; Litwin PE; Martin JS; Kudenchuk PJ; Eisenberg M SO - JAMA 1993 Sep 8;270(10):1211-6. Halving of mortality at 1 year by domiciliary thrombolysis in the Grampian Region Early Anistreplase Trial (GREAT). AU - Rawles J SO - J Am Coll Cardiol 1994 Jan;23(1):1-5. Rawles, J. GREAT: 10 year survival of patients with suspected acute myocardial infarction in a randomised comparison of prehospital and hospital thrombolysis. Heart 2003; 89:563. Hope this Helps, ACE844

(Best Practice & Research Clinical Anaesthesiology Volume 19 @ Issue 4 , December 2005, Pages 699-715 Difficult Airway Management doi:10.1016/j.bpa.2005.07.003 Copyright © 2005 Elsevier Ltd All rights reserved. 10 Airway management in emergency situations Volker Dörges MD, , Department of Anaesthesiology and Intensive Care Medicine, University Hospital Schleswig-Holstein, Campus Kiel, Schwanenweg 21, D-24105 Kiel, Germany Available online 5 December 2005.) Securing and monitoring the airway are among the key requirements of appropriate therapy in emergency patients. Failures to secure the airways can drastically increase morbidity and mortality of patients within a very short time. Therefore, the entire range of measures needed to secure the airway in an emergency, without intermediate ventilation and oxygenation, is limited to 30–40 seconds. Endotracheal intubation is often called the ‘gold standard’ for airway management in an emergency, but multiple failed intubation attempts do not result in maintaining oxygenation; instead, they endanger the patient by prolonging hypoxia and causing additional trauma to the upper airways. Thus, knowledge and availability of alternative procedures are also essential in every emergency setting. Given the great variety of techniques available, it is important to establish a well-planned, methodical protocol within the framework of an algorithm. This not only facilitates the preparation of equipment and the training of personnel, it also ensures efficient decision-making under time pressure. Most anaesthesia-related deaths are due to hypoxaemia when difficulty in securing the airway is encountered, especially in obstetrics during induction of anaesthesia for caesarean delivery. The most commonly occurring adverse respiratory events are failure to intubate, failure to recognize oesophageal intubation, and failure to ventilate. Thus, it is essential that every anaesthesiologist working on the labour and delivery ward is comfortable with the algorithm for the management of failed intubation. The algorithm for emergency airway management describing the sequence of various procedures has to be adapted to internal standards and to techniques that are available. Airway management in obstetrics Although the use of general anaesthesia for caesarean delivery has dramatically declined during recent decades, it is still necessary for the management of several situations, including maternal haemorrhage, overt coagulopathy, life-threatening fetal compromise, or cases in which patients refuse regional anaesthesia. A recent study found that anaesthesia-related maternal mortality associated with regional anaesthesia has declined, but that the number of deaths involving general anaesthesia has remained relatively constant. Thus, the relative risk of fatality during general anaesthesia has increased to more than 16 times that for regional anaesthesia.1 While general anaesthesia has the advantage of speed of induction, control of the airway, and superior haemodynamics, potential problems associated with general anaesthesia for caesarean section include failed intubation and pulmonary aspiration of gastric contents; it is therefore essential that every anaesthesiologist working on the labour and delivery ward is comfortable with the algorithm for the management of failed intubation (Figure 1). (55K) Figure 1. Management of difficult intubation in pregnancy. etCO2, end-tidal carbon dioxide; SpO2, oxygen saturation; ILMA, intubating laryngeal mask airway; LMA, laryngeal mask airway; ETC, oesophageal/tracheal Combitube; LT, laryngeal tube; LTS, laryngeal tube with suction port; EzT, Easytube. Most anaesthesia-related deaths were due to hypoxaemia when difficulty in securing the airway was encountered. The most commonly occurring adverse respiratory events are failure to intubate, failure to recognize oesophageal intubation, and failure to ventilate. Physical factors seen in pregnancy–such as weight gain, enlarged breasts, and oropharyngeal oedema–can complicate endotracheal intubation. Central to decreasing the risk associated with general anaesthesia is early assessment of the mother's airway. When evaluating the risk factors associated with difficult intubation, it has been suggested that the greatest risks are associated with a Mallampati class 4 airway: a short neck, protruding maxillary incisors, and mandibular recession.2 Regardless of the initial assessment, all patients must have a repeat airway examination performed before initiation of anaesthesia for caesarean section because it has been demonstrated that labour may be associated with changes in the maternal airway.3 Prehospital emergency airway management Securing and monitoring the airway in emergency patients are among the key requirements of appropriate pre-hospital therapy. Besides taking patient-specific anatomical and functional problems into account, it is important to consider difficulties that may arise in an emergency setting, as in the case of trauma or inflammatory disease of the upper respiratory tract. Failures to secure the airways can drastically increase the morbidity and mortality of patients within a very short time. Therefore, the entire range of measures needed to secure the airway in an emergency, without intermediate ventilation and oxygenation, is limited to 30–40 seconds. The condition of the patient and the underlying diseases or injuries dictate the urgency of the measures as well as the techniques to be used and the associated risk. However, the best procedure in every individual case also depends on the equipment that is available and on the physician's level of expertise and experience. Endotracheal intubation is often called the ‘gold standard’ for airway management in a pre-hospital setting, but knowledge and availability of alternative procedures are also essential for every emergency physician. Moreover, every emergency physician must be able to identify patients who present potential problems of airway management and should be familiar with the methods used to classify them. By anticipating difficulties and addressing them early, the physician can often avoid potentially life-threatening situations for the patient. Multiple failed intubation attempts do not result in maintaining oxygenation, the key objective of all measures taken by the emergency physician; instead, they endanger the patient by prolonging hypoxia and causing additional trauma to the upper airways. Repeated laryngoscopy may cause swelling, mucosal lesions and bleeding, worsening the condition of the upper airways and lowering the success rate. Given the great variety of techniques available, it is important to establish a well-planned, methodical protocol within the framework of an algorithm. This not only facilitates the preparation of equipment and the training of personnel, but also ensures efficient decision-making under time pressure. Characteristics of the pre-hospital emergency situation Difficulties and complications in securing the airway occur more often during intubation in emergency situations than during planned induction of anaesthesia.4 The reasons for this include—in addition to patient-specific factors—a lack of appropriate equipment, environmental conditions very different from those in the hospital setting (such as inclement weather or poor lighting), as well as limited access to the patient. For planned induction of anaesthesia, Benumof cites a 1–10% incidence of problems with endotracheal intubation, depending on the subgroup of patients.5 Recently published data from Thierbach et al are in full agreement with findings of other authors that the incidence of airway management problems is significantly increased in pre-hospital settings compared with airway management in hospitalized patients.6 In this study, airway management was performed without incident in 80%, while adverse events or complications were documented in 20% of the patients. In 1.5% of the cases, supraglottic airway devices (such as the Combitube or laryngeal mask airway) or cricothyrotomy were employed after the third failed intubation attempt. Additionally, patients with severe trauma were found to have a higher incidence of adverse events and complications than non-traumatized patients. In particular, the number of intubation attempts was higher in trauma patients.Diseases and trauma that affect airway management include: • cervical spine injuries; • midfacial and maxillary injuries; • soft-tissue injuries of the neck; • thermal injuries; • obstruction by foreign bodies; • epiglottitis. In these studies, aspiration was the second most common adverse event. As a matter of policy, emergency patients are classified as non-fasted, and, therefore, have a much greater likelihood of regurgitating and then aspirating gastric contents. The physiological mechanism that protects against regurgitation is abolished by relaxation of the lower oesophageal sphincter and extinction of protective reflexes due, for example, to cardiac arrest. Moreover, the risk of aspiration is further increased by chest compressions, mask ventilation, and positioning manoeuvres. For this reason, cricoid pressure (Sellick manoeuvre) should be applied during mask ventilation of non-fasted patients;7 this closes off the oesophagus, preventing inflow of air with the risk of overdistending the stomach during ventilation, and also preventing regurgitation of gastric contents. In pre-hospital emergency medicine, airway management mostly has to be provided by an emergency physician who is less skilled and experienced than an anaesthesiology specialist. At the same time, practical experience in emergency medicine without regular practice in anaesthesia is generally insufficient to meet the recommendations of the International Liaison Committee on Resuscitation (ILCOR). According to these recommendations, tracheal intubation of 6–12 emergency patients per year is required after appropriate initial training.8 Regular work in anaesthesiology or repeated training is essential for maintaining the necessary expertise and skills in order to meet these guidelines. Competence and experience of the assisting personnel (EMTs, paramedics) also plays a vital role in the success or failure of pre-hospital emergency airway management. Additionally, a multitude of variable external factors can make airway management difficult in pre-hospital emergency settings, compared to almost ideal conditions during in-hospital anaesthesia induction. These factors include the possibly unchangeable position of the patient and extreme lighting and weather conditions. Physically cramped conditions can make it difficult to gain access to the patient's head and may seriously limit the ability to secure the airway, and measures taken to optimize the patient's position may cause delays that prolong the period of hypoxia. If, for example, the patient is pinned inside a vehicle after a traffic accident and access is limited, it will be difficult or impossible to secure the airway by direct laryngoscopy. Indications for pre-hospital airway management In Central Europe, acute disorders account for more than 80% of the indications for pre-hospital airway management, while trauma patients account for only 10–20% of these cases.9 The most frequent indication for airway intervention is cardiac arrest. The following three criteria are considered general indications for securing the airway in a pre-hospital setting: • apnoea; • severe respiratory insufficiency; • Glasgow Coma Scale score <9. Prehospital intubation is also frequently indicated in patients with multiple injuries or severe craniocerebral trauma and in patients with a high aspiration risk that cannot be eliminated less invasively. The urgency of emergency airway intervention can be classified into three categories: • immediate intervention; • emergency intervention; • urgent intervention. The urgency of the situation will particularly determine the extent of necessary examinations and the assessment of the risks associated with interventional measures. Immediate orotracheal intubation should be attempted in all apnoeic patients. No further tests to determine risks or plan alternative procedures can be performed. Patients with severe respiratory distress or loss of consciousness require emergency intervention. However, in these situations little time is left to pre-oxygenate the patient, to perform a cursory check for potential intubation problems, and to prepare an adequate instrument setup for alternative airway management if the examination suggests that problems may arise. Patients with, for example, rapidly increasing swelling of the upper airway or injuries to the chest wall do not always show signs of acute respiratory decompensation, but present an urgent indication for securing the airway. Following oxygen administration, a selective examination can be conducted and a brief history taken. Furthermore, both pharmacological and equipment issues may be considered within the context of urgent intervention and appropriate preparations made with the goal of minimizing risks. In conclusion, before performing tracheal intubation, at least definitive signs of potential intubation problems should be identified if possible in order to avoid airway catastrophes: • decreased mobility of the cervical spine; • microgenia; • mouth opening <2 cm; • ankylosis of the temporomandibular joint (TMJ); • extreme macroglossia; • severe rheumatoid illnesses; • malformation syndromes; • scarring (after tumour surgery, burns, irradiation); • epiglottitis; • tumours obstructing the airway. Intubation is classified as difficult when successful placement of the endotracheal tube by conventional laryngoscopy requires more than three attempts or takes longer than 10 minutes. If neither intubation nor mask ventilation is possible, a ‘cannot intubate, cannot ventilate’ situation arises in which no time may be wasted in further intubation attempts. The immediate use of an alternative technique is recommended in this case. Techniques of airway management Monitoring Successful emergency airway management requires a structured protocol, which is known by all members of the emergency team. In addition to clinical examination techniques, the following instrumental monitoring is essential in emergency airway management both for diagnosis and for monitoring the patient during and after securing the airway: • pulse oximetry; • capnometry and capnography. With its easy handling, pulse oximetry has become a routine tool for monitoring respiratory function and oxygenation in emergency medicine and improving patient safety. Especially in adequately oxygenated patients, decrease of partial oxygen saturation in apnoea needs some time; therefore, pulse oximetry is not a useful procedure for checking the correct placement of an endotracheal tube. The main indication for capnometry is to verify the correct position of the endotracheal tube in patients with intact circulatory function10, but in arrested patients capnometry does not reliably indicate the correct position of the tube. While ventilatory monitoring by capnometry may be of limited usefulness due to possible ventilation–perfusion mismatch in some emergency patients, capnometry may serve as an important early warning system for ventilation system defects, which can be detected at once when the return flow of CO2 is absent or diminished.11 and 12 Oxygen delivery and clearing the airway In all patients who are still spontaneously breathing, sufficient oxygenation should be maintained by oxygen delivery in an adequate concentration. Additionally, in cases of partial or complete airway obstruction with fluids or solid foreign bodies in unconscious patients, the airway has to be cleared by suctioning or foreign body extraction with Magill forceps under visual control during laryngoscopy.13 Bag-valve-mask ventilation Bag-valve-mask (BVM) ventilation is a fundamental skill of emergency airway management and should receive a high priority in training. A ventilation bag with attached mask can be used to provide both assisted and controlled ventilation of the patient. Generally, a high-flow oxygen source (10 L/minutes) allows better compensation of facemask leaks and generation of sufficient positive pressure to overcome respiratory system resistance to gas flow. Jaw thrust and neck extension is usually necessary to provide a patent airway. The mask should be sized to cover the nose at the level of the nose bridge and the mouth just above the chin. Particularly in obese patients, the combination of redundant oropharyngeal soft tissue, a bulky tongue, and a thick chin and neck pad may interfere with the ability to ventilate. Several methods may be used to overcome this resistance. Lifting the chin pad while applying a jaw thrust can straighten the soft tissues of the anterior wall in the hypopharynx and facilitate ventilation. Early insertion of a plastic oral airway or tilting the head laterally while ventilating may reduce the risk of the tongue falling backward against the soft palate. Finally, two-person mask ventilation may be more effective and should be attempted. Several studies show that bag-valve-mask ventilation performed by both emergency physicians and health care professionals may be partially insufficient due to inexperience in mask ventilation14, resulting in an increased risk of gastric inflation with subsequent regurgitation and pulmonary aspiration.15 Also, the dramatic decrease in lower oesophageal sphincter pressure and respiratory system compliance in cardiac arrest may adversely affect the distribution of gas between the lungs and stomach during cardiopulmonary resuscitation (CPR) and direct larger volumes of gas towards the stomach rather than ventilating the lungs.16Disadvantages of mask ventilation during CPR include the following: • chest compressions are less effective, since synchronization with BVM ventilation is necessary; • there is no possibility of bronchial toilet and endobronchial medication; • decreased pulmonary compliance and lower oesophageal sphincter pressure increase the risk of gastric inflation and pulmonary aspiration. Limiting the size of the ventilation bag to a paediatric volume could theoretically decrease the danger of delivering an exaggerated tidal volume during CPR. However, if oxygen is not available at the scene of an emergency and small tidal volumes are given during BVM ventilation with a paediatric self-inflatable bag and room air (21% oxygen), insufficient oxygenation and/or inadequate ventilation may result.17 In a recent study, 40 patients were randomly allocated to room-air ventilation with either an adult or paediatric self-inflatable bag for 5 minutes while apnoeic after induction of general anaesthesia before intubation.17 When using the adult versus paediatric self-inflatable bag, tidal volumes per kilogram were significantly larger. Compared with an adult self-inflatable bag, BVM ventilation with room air using a paediatric self-inflatable bag resulted in significantly lower arterial partial pressure of oxygen values but comparable carbon dioxide elimination, indicating that smaller tidal volumes of about 6 mL/kg (approximately 500 mL) given with a paediatric self-inflatable bag and room air maintain adequate carbon dioxide elimination but not oxygenation during BVM ventilation. This study confirms previous observations that if small (6 mL/kg) tidal volumes are being used for BVM ventilation, additional oxygen is necessary, and when additional oxygen is not available only large tidal volumes of about 10–12 mL/kg can be used to maintain both sufficient oxygenation and carbon dioxide elimination. The performance of the apparatus used to deliver BVM ventilation has recently been extensively reviewed. Seven commercially available models of ventilating bags used on an advanced cardiac life support training mannequin connected to an artificial lung in which compliance and resistance were set at normal have been evaluated with regard to the tidal volume provided.18 Interestingly, standard ventilations with one hand averaged a tidal volume of 450–600 mL in both genders despite significant differences in the sizes of male and female hands. When the technique was modified to open palm and total squeezing of the self-inflating bag against the flexed rescuer's knee, next to the patient's head, total volume ranged from 900 to 1200 mL. This study seems to indicate that most of the commercially available ventilating bags can provide both the 5–6 and 10–12 mL/kg volume ventilation, as recommended by the 2000 International guidelines, with and without available oxygen, in a reliable manner. Endotracheal intubation Endotracheal intubation is used all over the world and is often called the ‘gold standard’ of airway management.19 The introduction of a cuff-sealed tube into the trachea offers significant advantages over BVM ventilation. The cuffed tube effectively seals the trachea up to peak airway pressures of approximately 50 mbar and prevents intrusion of solid or liquid foreign material. Advantages of endotracheal intubation compared to BVM ventilation: • secure ventilation with airway patient-adjusted airway pressures; • optimum protection against aspiration; • option of endobronchial medication (e.g. epinephrine, lidocaine, atropine, naloxone); • bronchial suction. General indications for tracheal intubation of emergency patients include, besides inability to breath spontaneously, all conditions in which spontaneous breathing is so severely compromised that there is risk of further damage: • cardiopulmonary resuscitation; • severe dyspnoea or respiratory depression; • patient with multiple injuries; • head-injured patient; • high risk of regurgitation and aspiration. There are no contraindications for tracheal intubation in an emergency. In trauma patients with suspected cervical spine injury, however, all measures should be carried out with an assistant stabilizing the neck in neutral position. Performing tracheal intubation, especially in an emergency, requires excellent skills and experience with this relatively complex technology and, additionally, it is necessary to monitor and reliably confirm the placement of the tube tip in the trachea. Undetected oesophageal intubation and inadvertent, unnoticed extubation of the trachea are the most serious incidents in airway management, as they can result in extremely severe hypoxic injury or even death. This underscores the importance of confirming correct endotracheal tube placement. Standard practice for intubation in an emergency is use of a laryngoscope with a Macintosh blade and a sufficiently large tube with stylus inserted. But even with improved training and performance the Macintosh technique has the disadvantage of a significant failure rate. In these cases, it is right to try alternative methods to achieve tracheal intubation. The most popular techniques for management of unexpected difficult intubation have been all blind intubation techniques: for example, usage of bougies and stylets, or securing the airway using alternative techniques of intubation under vision. The technique of passing a gum elastic bougie blindly into the trachea, over which a tracheal tube is then threaded, was described by Macintosh. There have been numerous reports of successful intubations with this technique, but neither passage of the bougie nor subsequent ‘railroading’ of the tracheal tube is universally successful, especially in seriously difficult tracheal intubation. In addition, all blind techniques can produce trauma. Laryngeal damage, oesophageal intubation, and haemopneumothorax have been reported. Repeated attempts at blind intubation can cause glottic damage and lead to a ‘cannot intubate, cannot ventilate’ situation. Use of a stylet (usually a ‘hockey-stick’ shape) to pre-form or stiffen a tracheal tube can facilitate guidance through the glottis when this is seen, or can be used as a blind technique with a narrow tracheal tube. Just as with the blind bougie technique, use of the stylet should be limited to a couple of attempts. There is no place for repeated use of blind techniques in modern anaesthetic practice. However, the Macintosh technique and blind techniques are not enough to prevent rare, avoidable disasters with tracheal intubation. A number of alternative techniques of intubation under vision, described below, have proved valuable when the Macintosh technique fails. The McCoy levering laryngoscope has a hinged tip, which is controlled by a lever on the handle. It is designed to lift the epiglottis without excessive leverage. Its use does not require special training. The McCoy laryngoscope is successfully used in patients with potential cervical spine fractures who are intubated with manual in-line stabilization of the cervical spine. It has a definite role in difficult intubations, though there is some doubt about its efficacy in the most difficult grade 4 patients. Straight blades are often preferred in infants and small children. Unlike curved blades, they can be used to lift the epiglottis, providing a better view of the larynx and the glottic plane.20 In contrast, performing the paraglossal straight blade technique with the Miller, Foregger, Philipps, or Henderson laryngoscopes may not be the best choice in the case of anticipated cervical spine injury, since flexion of the neck and rotation of the head may become necessary when intubation is difficult. Perhaps a newly developed universal blade, designed for tracheal intubation in emergency situations, may be helpful, since—in addition to other features—the low profile of this blade (with a height of 16 mm) makes rapid intubation easy, even in an emergency with restricted mouth opening. The design of the Dörges laryngoscope blade allows tracheal intubation of all patients >22 lb, and to replace the traditional Macintosh blades sizes 2–4. The benefit will be a significant reduction in the number of blades that need to be kept for emergency intubation, and therefore more effective use of limited space and a reduction in weight and costs.21 If direct laryngoscopy with visualization of the larynx proves impossible during the first attempt, the following measures may be helpful to complete intubation successfully even under challenging anatomical conditions: • place the head in modified Jackson position (‘sniffing position’); • have an assistant applying cricoid pressure; • perform the BURP (backward upward rightward pressure) manoeuvre to move the larynx closer to the visual axis of the intubator; • select a tube with an internal diameter 1.0 mm smaller; • bend the tube into a ‘hockey stick’ shape with a stylus; • advance the stylus until it projects 1–2 cm past the tube tip; • use a laryngoscope blade with a different shape or size. Blind nasal intubation Nowadays in emergency airway management the blind nasal intubation technique is very rarely used. This procedure requires great experience and should be used only in highly selected cases such as securing the airway in spontaneously breathing patients with no cervical spine or skull injuries. Technically complex intubation procedures Flexible intubation fibrescopes (FIFs) are the most effective solution in all cases of anticipated difficult intubation in a spontaneously breathing patient. If a FIF is equipped with a small, intense, battery-powered light source, its use is not limited to conventional anaesthesia settings or the intensive care unit. Furthermore, it can easily be transported to the patient, and therefore is suited for universal use in the hospital or even in pre-hospital emergency airway management.22 Of course, the use of flexible intubation fibrescopes requires extended skills with continuous training and appropriate logistics, especially with regard to cleaning and disinfecting the FIF after each use. Therefore, the rigid Bonfils intubation fibrescope (BIF) with the aid of indirect laryngoscopy may expand the options for endotracheal intubation in case of an unexpected difficult airway.23 This rigid fibrescope simplifies orotracheal intubation of patients with various problems that may prohibit successful direct laryngoscopy, such as restricted mouth opening, an immobilized cervical spine, a large tongue, or mandibular retrognathia.24 This intubation technique by indirect laryngoscopy is not only more complex than standard laryngoscopy but also requires clinical experience and continuous practice. Compared to the flexible intubation fibrescope, urgent management of a difficult airway with the rigid Bonfils fibrescope has some advantages: ruggedness, relative technical simplicity (battery-powered light source), ability to be cleaned quickly and easily, and significantly lower cost. Supraglottic procedures Proficiency in alternative techniques for establishing airway access is of crucial importance when routine measures fail. Intensive training in these situations, as well as protocols based on standardized guidelines and algorithms, allow recognition of common problems and institution of appropriate therapeutic measures without delay. While supraglottic procedures allow for blind positioning of the airway device, the airways in these cases cannot be inspected for trauma, bleeding, foreign bodies, or other pathology. As a general rule, all supraglottic procedures are contraindicated in patients who have ingested caustic substances or have other upper respiratory tract diseases tending to cause significant swelling. Supraglottic airway devices Combitube The oesophageal/tracheal Combitube (ETC) is primarily used as an emergency tube for ventilating patients during resuscitation.25 It provides a complete seal of the upper airway and can therefore be used in patients with a high risk of regurgitation and aspiration of gastric contents.26 It has two lumina, one of which resembles a conventional endotracheal tube while the other seals off the oesophagus with an oropharyngeal balloon. The ETC can be inserted blindly through the mouth and is more likely to pass into the oesophagus (>95%) than into the trachea (<5%). It can safely be inserted in patients with cervical spine injuries because flexion of the neck is not required. This device is only available in two sizes: ‘adult’ and ‘small adult’ for patients >122 cm in height. It is classified as a ‘backup device’ which is used mainly for rapid airway establishment and oxygenation in emergencies.27 The most common reason for ventilation failure with this device is placement of the device too deeply, so that the perforated pharyngeal section has entirely entered the oesophagus. Pulling the Combitube back 3–4 cm usually resolves the problem. However, it is not well tolerated in patients with a persistent strong gag reflex after resuscitation and should be exchanged with an alternative airway as soon as possible. Laryngeal mask airway The laryngeal mask airway (LMA) has found worldwide distribution since it was described in 198528, and is used in many anaesthesiological procedures. It is described as a tool for performing ‘something that is between mask and endotracheal anaesthesia’. With the cuff around its elliptical body, the LMA seals the larynx posteriorly and enables ventilation of the patient without intubating the trachea. The LMA is available in all sizes from infant to adult and allows, with some experience, rapid manual positioning without additional aids in anaesthetized or unconscious patients. Numerous reports document the successful use of the LMA in emergencies under difficult conditions29, during CPR30, and in trauma patients31 even by non-physicians. Since leakage occurs when peak airway pressure exceeds 20 mbar, ventilation with the LMA requires synchronization between chest compressions and ventilation during CPR to avoid over-distension of the stomach. Intubating laryngeal mask airway The intubating laryngeal mask airway (ILMA) is an advanced version of the LMA allowing a special endotracheal tube to be passed through the ILMA into the trachea.32 Its use is recommended especially in case of difficult intubation, after failed intubation attempts, and for rescuers inexperienced in tracheal intubation. Therefore, the ILMA may provide a solution for the unexpected difficult airway especially when in-line neck stabilization is necessary, since this device does not require visualization of the vocal cords before being placed. Meanwhile, the ILMA has been well established, and a high cumulative success rate (>95%) with a maximum of three attempts is reported for this device33, which has been used successfully in many instances of failed tracheal intubation. This device follows a two-step concept: (1) it may be used as a rescue airway when tracheal intubation has failed and in ‘cannot intubate, cannot ventilate’ situations, allowing rapid oxygenation and ventilation; and (2) it serves for securing the airway as a conduit for tracheal intubation through the ILMA (blind or under vision). In future, the JLMA may replace the LMA because of its greater flexibility with regard to rapid oxygenation and securing the airway in an emergency when used by professional rescuers. Laryngeal tube The laryngeal tube (LT) consists of a single-lumen reusable or disposable tube with a pharyngeal and oesophageal cuff which seals the pharyngeal airway and also the oesophageal inlet, and a ventilation outlet in between.34 It is available in all sizes from newborns to tall adults. After manual placement without a laryngoscope, both the pharyngeal and oesophageal cuffs are inflated through a common line. Placement of the LT is easy, and the device provides an effective seal for peak airway pressures up to 40 mbar.34 Its pre-hospital use in emergency patients has been described in several case reports.35 The simple-to-handle LT may be the appropriate device when basic ventilatory life support has to be performed by health-care professionals untrained in emergency airway management. Perhaps this device may be the best choice to replace the BVM system in future. Laryngeal tube with suction port (LTS) The LTS is an advanced version of the LT, providing a second lumen serving for gastric drainage or insertion of a gastric tube but not for ventilation.36 The LTS therefore offers even better protection from aspiration than the LT and is available in sizes for small up to tall adults. Easytube (EzT) The EzT is a disposable device for use in anticipated and unexpected difficult airways; it combines the essential features of an endotracheal tube with those of a supraglottic airway device.37 It consists of two lumina that allow ventilation with the tip of the tube in either tracheal or oesophageal position. A large oropharyngeal cuff ensures sealing of the airway from the oro- and nasopharynx. A ‘high volume/low pressure cuff’ is attached to the tip of the tube, resembling a standard endotracheal tube. The EzT is available in two sizes for children >90 cm up to tall adults. Evaluation of supraglottic airway devices In the 2000 ILCOR guidelines, endotracheal intubation is cited as the optimum technique for airway management, but supraglottic devices are explicitly mentioned as alternatives.8 These alternative devices are described as suitable for use by providers with only limited experience in endotracheal intubation, but also for use in case of failed initial intubation attempts. According to evidence-based criteria the ETC and LMA are evaluated and classified as follows: • ETC and LMA are easier to place compared to endotracheal intubation; • ventilation with both devices is comparable to that obtained with an endotracheal tube and is definitely superior to BVM ventilation; • complication rates are comparable to those of endotracheal intubation; • ETC and LMA are effective in cases of failed endotracheal intubation. Both the ETC and the LMA are therefore recommended as acceptable, safe, and helpful alternatives.38 There is no question that at least one of the supraglottic airway devices described above should be immediately available in an emergency when laryngoscopic endotracheal intubation fails. Surgical airway The ‘surgical airway’ is strictly a means of last resort. It is indicated when the airway cannot be secured by endotracheal intubation or by an alternative technique and BVM ventilation is not possible. A surgical airway can be life-saving, especially in patients with massive oropharyngeal swelling caused by tumour, insect bite, profuse bleeding after injury to the facial skeleton, or airway obstruction by a non-extractable foreign body. As a rule, a surgical airway is established by cricothyrotomy (coniotomy) in adults and by ‘transtracheal ventilation’ in children up to 10 years. Depending on the available equipment and personnel's skills, a surgical airway must be established in a pre-hospital setting in approximately 2–15% of cases.39 and 40 The availability of alternative airway devices and highly trained personnel may significantly lower the incidence of this very invasive measure. Position check Especially in urgent emergency airway management, all described techniques of securing the airway include the potential risk of undetected placement errors—usually oesophageal intubation. Even after correct placement, accidental and unnoticed dislocation of an endotracheal tube or another device may occur. In infants and small children, whose trachea is less than 10 cm in overall length, even slight manipulations carry a risk of dislodging the tube from the airway. Thus, checking the correct placement of every device and safeguarding against accidental dislodgement are essential in pre-hospital and clinical emergency medicine. With the exception of direct laryngoscopy to monitor the tube passing the vocal cords, all clinical tests and procedures are classified as unreliable indicators of accurate endotracheal intubation. Unreliable tests and indicators for checking endotracheal tube placement include: • bilateral chest auscultation (apical, basal); • auscultation of the epigastrium; • observation of equal chest excursions on both sides; • condensation of expiratory air in the endotracheal tube during initial expiration. On the other hand, capnography has established itself as the most important instrumental method for verifying tube position in clinical anaesthesia. Classified as fairly reliable, this method has also been used increasingly in emergency medicine during recent years.41 Problems with verifying correct endotracheal tube placement by capnometry arise most commonly in cardiac arrest patients. Lung perfusion during chest compressions does not produce end-expiratory carbon dioxide concentrations sufficient to establish whether the tube is placed in the trachea or oesophagus.42 Another fairly reliable procedure is the oesophageal detection method based on the use of the oesophageal detector devices. With this method, air is suctioned abruptly from the tube using a small rubber bulb or large volume syringe. Unlike the muscular oesophagus, the trachea will not collapse in response to the resulting negative pressure, as it is stabilized by cartilage rings. Therefore, the oesophageal detector device will only inflate when the tube is correctly placed in the trachea. Fairly reliable methods of verifying endotracheal tube position include: • capnography or capnometry; • oesophageal detector device. The oesophageal detector device method is preferred in cardiac arrest patients over the CO2 detection method43 and is an integral part of the current ILCOR recommendations.44 Algorithm This algorithm for emergency airway management describes the sequences of the various described procedures (Figure 2). However, it must be adapted to internal standards and to techniques that are available. (71K) Figure 2. Emergency airway management algorithm. etCO2, end-tidal carbon dioxide; SpO2, oxygen saturation; ILMA, intubating laryngeal mask airway; LMA, laryngeal mask airway; ETC, oesophageal tracheal Combitube; LT, laryngeal tube; LTS, laryngeal tube with suction port; EzT, Easytube. If the first intubation attempt fails, it should be discontinued after 40 seconds at most in order to oxygenate the patient by BVM ventilation. If this is also unsuccessful, a ‘cannot intubate, cannot ventilate’ situation exists requiring an immediate switch to an alternative approach—generally a supraglottic procedure. Failed intubation manoeuvres should be discontinued after the third attempt at the latest and alternative procedures applied in order to maintain oxygenation and avoid further airway deterioration. If these alternatives also fail, surgical access should be established without any further delay. A position check is mandatory after placement of every endotracheal tube or alternative device. The entire duration of the process leading to a secure airway in a patient requiring immediate intubation should not exceed the individual hypoxic tolerance of the patient, even when complications arise. References 1 J.L. Hawkins, L.M. Koonin and S.K. Palmer et al., Anesthesia-related deaths during obstetric delivery in the United States, 1979–1990, Anesthesiology 86 (1999), pp. 277–284. 2 D.A. Rocke, W.B. Murray and C.C. Rout et al., Relative risk analysis of factors associated with difficult intubation in obstetric anesthesia, Anesthesiology 77 (1992), p. 67. Abstract-MEDLINE | Abstract-EMBASE 3 E.L. Farcon, M.H. Kim and G.F. Marx, Changing Mallampati score during labor, Can J Anaesth 41 (1994), pp. 50–51. Abstract-EMBASE | Abstract-MEDLINE 4 J.V. Doran, B.J. Tortella and W.J. Drivet et al., Factors influencing successful intubation in the prehospital setting, Prehosp Disaster Med 10 (1995), pp. 259–264. Abstract-MEDLINE 5 J.L. Benumof, Management of the difficult adult airway with special emphasis on awake tracheal intubation, Anesthesiology 75 (1991), pp. 1087–1110. Abstract-MEDLINE | Abstract-EMBASE 6 A. Thierbach, T. Piepho and B. Wolcke et al., Erfolgsraten und Komplikationen bei der präklinischen Sicherung der Atemwege (German), Der Anaesthesist 53 (2004), pp. 543–550. Abstract-EMBASE | Abstract-MEDLINE 7 I. Landsman, Cricoid pressure indications and complications, Paediatr Anaesth 14 (2004), pp. 43–47. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 8 Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care: adjuncts for oxygenation, ventilation and airway control. Circulation 2000; 102:I-95–I-104. 9 S.B. Karch, T. Lewis and S. Young et al., Field intubation of trauma patients, Am J Emerg Med 14 (1996), pp. 617–619. SummaryPlus | Full Text + Links | PDF (338 K) 10 G. Petroianu, W. Maleck and W.F. Bergler et al., Preclinical control of intubation and artificial respiration. Animal experiment and literature review (German), Anaesthesist 44 (1995), pp. 613–623. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 11 K.R. Ward and D.M. Yealy, End-tidal carbon dioxide monitoring in emergency medicine. Part 1. Basic principles, Acad Emerg Med 5 (1998), pp. 628–636. Abstract-EMBASE | Abstract-MEDLINE 12 K.R. Ward and D.M. Yealy, End-tidal carbon dioxide monitoring in emergency medicine. Part 2. Clinical applications, Acad Emerg Med 5 (1998), pp. 637–646. Abstract-EMBASE | Abstract-MEDLINE 13 M. Lipp and W. Dick, Airway occlusion as an emergency. Recognition and treatment (German), Internist 36 (1995), pp. 765–768. Abstract-MEDLINE | Abstract-EMBASE 14 E.G. Lawes and P.J. Baskett, Pulmonary aspiration during unsuccessful cardiopulmonary resuscitation, Intensive Care Med 13 (1987), pp. 379–382. Abstract-MEDLINE 15 B.J. Stone, P.J. Chantler and P.J.F. Baskett, The incidence of regurgitation during cardiopulmonary resuscitation: a comparison between the bag valve mask and laryngeal mask air-way, Resuscitation 38 (1998), pp. 3–6. Abstract 16 V. Wenzel, A.H. Idris and M.J. Banner et al., Influence of tidal volume on the distribution of gas between the lungs and the stomach in the nonintubated patient receiving positive pressure ventilation, Crit Care Med 26 (1998), pp. 364–368. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 17 V. Dorges, H. Ocker and S. Hagelberg et al., Smaller tidal volumes with room air are not sufficient to ensure adequate oxygenation during bag-valve-mask ventilation, Resuscitation 44 (2000), pp. 37–41. Abstract 18 B. Wolcke, T. Schneider and D. Mauer et al., Ventilation volumes with different self-inflating bags with reference to ERC guidelines for airway management: comparison of two compression techniques, Resuscitation 47 (2000), pp. 175–178. Abstract 19 P.J.F. Baskettt, L. Bossaert and P. Carli et al., Guidelines for the advanced management of the airway and ventilation during resuscitation, Resuscitation 31 (1996), pp. 201–230. 20 J.J. Henderson, The use of paraglossal straight blade laryngoscopy in difficult tracheal intubation, Anaesthesia 52 (1997), pp. 552–560. Abstract-EMBASE | Abstract-MEDLINE 21 K. Gerlach, V. Wenzel and G. von Knobelsdorff et al., A new universal laryngoscope blade: a preliminary comparison with Macintosh laryngoscope blades, Resuscitation 57 (2003), pp. 63–67. Abstract 22 A. Thierbach and M. Lipp, Fiberoptic intubation in prehospital emergency medicine (German), Notfall und Rettungsmedizin 2 (1999), pp. 105–110. Full Text via CrossRef 23 B. Bein, M. Yan and P.H. Tonner et al., A comparison of the intubating laryngeal mask airway and the Bonfils intubation fibrescope in patients with predicted difficult airways, Anaesthesia 59 (2004), pp. 668–674. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 24 B. Bein, F. Worthmann and J. Scholz et al., Tracheal intubation using the Bonfils intubation fibrescope after failed direct laryngoscopy, Anaesthesia 59 (2004), pp. 1207–1209. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 25 M. Frass, R. Frenzer and F. Rauscha et al., Evaluation of the esophageal tracheal combitube in cardiopulmonary resuscitation, Crit Care Med 15 (1987), pp. 609–611. Abstract-EMBASE | Abstract-MEDLINE 26 D.P. Lefrancois and D.G. Dufour, Use of the esophageal tracheal combitube by basic emergency medical technicians, Resuscitation 52 (2002), pp. 77–83. Abstract 27 C.J. Rumball and D. McDonald, The PTL, Combitube™, laryngeal mask and oral airway: a randomized prehospital comparative study of ventilatory device effectiveness and cost-effectiveness in 470 cases of cardiorespiratory arrest, Prehosp Emerg Care 1 (1997), pp. 1–10. Abstract-MEDLINE 28 A.I. Brain, T.D. Mc Ghee and E.J. McAteer et al., The laryngeal mask airway. Development and preliminary trials of a new type of airway, Anaesthesia 40 (1985), pp. 356–361. Abstract-EMBASE | Abstract-MEDLINE 29 A.I. Brain, Three cases of difficult intubation overcome by the laryngeal mask airway, Anaesthesia 40 (1985), pp. 353–355. Abstract-EMBASE | Abstract-MEDLINE 30 M. Grayling, I.H. Wilson and B. Thomas, The use of the laryngeal mask airway and Combitube in cardiopulmonary resuscitation: a national survey, Resuscitation 52 (2002), pp. 183–186. Abstract 31 C.D. Deakin, Prehospital management of the traumatized airway, Eur J Emerg Med 3 (1996), pp. 233–243. Abstract-MEDLINE 32 A.I. Brain, C. Verghese and E.V. Addy et al., The intubating laryngeal mask. II. A preliminary clinical report of a new means of intubating the trachea, Br J Anaesth 79 (1997), pp. 704–709. Abstract-MEDLINE 33 P.J. Baskett, M.J. Parr and J.P. Nolan, The intubating laryngeal mask, Results of a multicentre trial with experience of 500 cases, Anaesthesia 53 (1998), pp. 1174–1179. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 34 V. Dörges, H. Ocker and V. Wenzel, The laryngeal tube: a new simple airway device, Anesth Analg 90 (2000), pp. 1220–1222. Abstract-MEDLINE | Abstract-Elsevier BIOBASE | Abstract-EMBASE 35 T. Asai, S. Moriyama and Y. Nishita et al., Use of the laryngeal tube during cardiopulmonary resuscitation by paramedical staff, Anaesthesia 58 (2003), pp. 393–394. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 36 V. Dörges, H. Ocker and V. Wenzel et al., The laryngeal tube S: a modified simple airway device, Anesth Analg 96 (2003), pp. 618–621. 37 A.R. Thierbach, T. Piepho and M.O. Maybauer, A new device for emergency airway management: the Easytube, Resuscitation 60 (2004), p. 347. Abstract 38 T.A. Barnes, D. MacDonald and J. Nolan et al., Cary resuscitation and emergency cardiovascular care. Airway devices, Ann Emerg Med 37 (2001), pp. 145–151. 39 J.B. Fortune, D.G. Judkins and D. Scanzaroli et al., Efficacy of prehospital surgical cricothyrotomy in trauma patients, J Trauma 42 (1997), pp. 832–836. 40 T.G. Gerich, U. Schmidt and V. Hubrich et al., Prehospital airway management in the acutely injured patient: the role of surgical cricothyrotomy revisited, J Trauma 45 (1998), pp. 312–314. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 41 A.B. Sanders, Capnometry in emergency medicine, Ann Emerg Med 18 (1989), pp. 1287–1290. Abstract 42 J.P. Ornato, A.R. Garnett and F.L. Glauser, Relationship between cardiac output and the end-tidal carbon dioxide tension, Ann Emerg Med 19 (1990), pp. 1104–1106. Abstract 43 W.P. Bozeman, D. Hexter and H.K. Liang et al., Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation, Ann Emerg Med 27 (1996), pp. 595–599. SummaryPlus | Full Text + Links | PDF (625 K) 44 Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care: adjuncts for oxygenation, ventilation and airway control. Circulation 2000; 102:I-95–I-104.

Hello Everyone, My apologies, I just realized that Part of the 'Ron Walls' post was cut off... Here's the missing section. I have no idea how to move this closer to the original post, perhaps admin or the mods could help????? Thanks, ACE844

"Everyone," In addition to the material already posted above. Here is a great article which covers the assessment of analgesia under anesthesia. The majority of the study discusses 'perioperative' conditions, yet i am sure that we all know this info can be extarpolated to both the CCT-flight environment S/P RSI in the setting of contuing paralysis and sedation as well as initally. Hope This Helps, ACE844 [/font:4a8af3581b] [quote=Best Practice & Research Clinical Anaesthesiology Volume 20, Issue 1 , March 2006, Pages 161-180 Monitoring Consciousness doi:10.1016/j.bpa.2005.09.002 Copyright © 2005 Elsevier Ltd All rights reserved. 14 Monitoring analgesia Bruno Guignard MD, Département d'Anesthésie Réanimation, Hôpital Ambroise Paré, 9 avenue du général de Gaulle, 92100 Boulogne Billancourt, France Available online 17 March 2006.] Analgesia (pain relief) amnesia (loss of memory) and immobilisation are the three major components of anaesthesia. The perception of pain, and therefore, the need for analgesia, is individual, and the monitoring of analgesia is indirect and, in essence, of the moment. Under general anaesthesia, analgesia is continually influenced by external stimuli and the administration of analgesic drugs, and cannot be really separated from anaesthesia: the interaction between analgesia and anaesthesia is inescapable. Autonomic reactions, such as tachycardia, hypertension, sweating and lacrimation, although non-specific, are always regarded as signs of nociception or inadequate analgesia. Autonomic monitoring techniques, such as the analysis of heart rate variability, laser Doppler flowmetry, phlethysmographically derived indices and the pupillary light reflex, may help to quantitate reactions of the autonomic nervous system. For the past few years, automated electroencephalographic analysis has been of great interest in monitoring anaesthesia and could be useful in adapting the peroperative administration of opioids. A range of information collected from the electroencephalogram, haemodynamic readings and pulse plethysmography might be necessary for monitoring the level of nociception during anaesthesia. Information theory, multimodal monitoring, and signal processing and integration are the basis of future monitoring. Monitoring analgesia Definitions Anaesthesia is a state of unconsciousness induced by a drug. The three components of anaesthesia are analgesia (pain relief), amnesia (loss of memory) and immobilisation, even though some authors have tried to reduced anaesthesia to a lack of perception or recall of noxious stimulation.1 The drugs used to achieve anaesthesia usually have varying effects in each of these areas. Some drugs may be used individually to achieve all three targets, whereas others have only analgesic or sedative properties and may be used individually for these purposes or in combination with other drugs to achieve full anaesthesia. Physiological methods of monitoring must be used to assess anaesthetic depth as normal reflex methods will not be reliable. The major problem is to define what anaesthesia and analgesia really are. In this regard combinations of anaesthetics and analgesics, known as ‘balanced anaesthesia’, do not help to provide a practical understanding of the concept of depth of anaesthesia paradigm.2 Pain is one of the most unpleasant sensations in existence, and even in fetal life noxious stimulation causes detectable stress responses. The prevention and treatment of pain are a basic human right, so a better comprehension of the detailed action of analgesics on pain relief is a challenge for the future.3 There have been many reports on pain research from various fields of medical science, for example physiology, pharmacology, biochemistry and immunology, and the knowledge acquired of the mechanisms of pain perception in the human brain can be directly related to the treatment of pain and the monitoring of pain relief. Pain is a more complicated sensation than other somatosensory modalities such as touch and vibration, as the degree of feeling can be easily changed by a change in mental state, pain being, by its very nature, subjective. In conscious subjects, pain is greatly affected by the amount of attention paid to and distraction from a noxious stimulus, but this is not the case under sedation or general anaesthesia. Human, as well as animal, studies on pain perception are necessary, but only a relatively small number of the former have been carried out because such studies must be non-invasive. Recently, non-invasive techniques have been developed, such as electroencephalography (EEG), magnetoencephalography, positron emission tomography, functional magnetic resonance imaging and transcranial magnetic stimulation, and the number of reports on pain perception using these techniques has progressively increased over the past 10 years.4, 5, 6 and 7 Analgesia is defined by the relief of pain, in other words by absence of pain in response to stimulation that would normally be painful. This definition is subjective because pain is defined by the International Association for Study of Pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Pain is a subjective sensation because of this individuality and is also difficult to assess because of the inability to communicate directly about the sensation of pain. Instead, indirect clinical signs of pain are used during anaesthesia. Because of the difficulty in determining when pain is present during general anaesthesia, it is assumed that something that is painful involves reactions of the body that are visible by clinical observation or by monitoring. Analgesia could also be defined by the combination of a stable state and the absence of pain—if the subject were conscious—during and immediately after a painful stimulus. One of the great paradoxes of analgesia is that, by its very nature, it cannot be predicted because of the perpetual interaction between variations in stimulation and variations in the patient's anaesthetized state. Like anaesthesia, analgesia is a continuum between a perceived absence of pain and maximum pain. Analgesia can be partial and incomplete, and the notion of a threshold of analgesia depends on the state of the patient and is continually under influence of external stimuli. Which parameters should be used to monitor analgesia? Individual perception of pain This chapter does not aim to consider the auto-evaluation of pain: a discussion of quantitative sensory testing of the nociceptive system in conscious subjects can be found in an article by Dotson.8 Instead, we will look at methods that could be used in unconscious patients; elucidating the mechanisms underlying pain perception in unconscious subjects could help us to understand analgesia. There is a relationship between the pain system and the motor, sensory and autonomic systems. Alterations to these systems, for example in a child with a significant neurological impairment, can have a profound and unique impact on the pain experience and analgesia.9 Likewise, hypoalgesia in borderline personality disorders may primarily be due to altered intracortical processing similar to that seen in certain meditative states: there is no general impairment of the sensory-discriminative component of pain, no hyperactive descending inhibition, and no attention deficits revealed by laser evoked potentials.10 There are also gender differences in pain perception11, 12 and 13, which might be of clinical relevance in morphine titration.14 These differences could be explained by a more pronounced descending inhibitory control.15 Nevertheless, there is no difference in desflurane minimum alveolar concentration (MAC) between young men and women.16 Clinical variation in the perception of analgesia Both the Ramsay Sedation Score and the Observer's Assessment of Alertness/Sedation Scale include response to pain in their graduated scales, reflecting an abolition of conscious pain perception.17 and 18 The Cardiac Analgesic Assessment Scale is a postoperative pain evaluation instrument used in children after cardiac surgery, providing more information than a visual analogue scale completed by an observer.19 Studies performed with anaesthetic personnel show that no variable was considered entirely specific for either intraoperative pain or depth of anaesthesia. Changes in breathing rate and volume, blood pressure, heart rate and lacrimation, as well as the presence of moist and sticky skin, were given higher scoring values as indicators of pain than as indicators of depth of anaesthesia.20 Movement and minimum anaesthetic concentration Under general anaesthesia, movement in response to painful stimulation is the end-point classically used to assess the potency of anaesthetic agents. Withdrawal reflexes are tailored to produce the most appropriate movement according the site at which the noxious stimulus is applied, as flexors or extensors could act as the primary movers. Areas from which a reflex can be sensitised closely match those from which the reflex itself can be evoked, providing the spinal cord is intact.21 The principal site of response to nociceptive stimulation is spinal22, and the interaction between analgesia and anaesthesia is inescapable. Interconnection between haemodynamics and nociception Somatosympathetic reflexes have been characterised for more than 30 years23, but the exact interaction between systems is still being researched because relationships are complexes.24 and 25 Some neurones from the rostral ventrolateral medulla have spinally projecting axons, and their responses to noxious mechanical, thermal and/or electrical stimulation have been shown to be accompanied by increases in arterial pressure in anaesthetised rats. In humans with spinal cord transection above vertebral level T5, profound elevations in systolic blood pressure and pulse pressure were induced by bladder distension: the authors noticed a decrease in heart rate in three of seven patients.26 A baroreflex mechanism may explain hypertensive hypoalgesia. At rest, arterial baroreceptors are stimulated during the systolic upstroke of the pressure pulse wave. Stimulation of the baroreceptors by natural increases in blood pressure during the systolic phase of the cardiac cycle was associated with dampened nociception. There are also interactions between angiotensin and pain perception. Untreated hypertensive subjects showed a reduced perception to painful stimuli when compared with normotensive individuals. A significant reduction in both pain threshold and tolerance was observed during enalapril or losartan treatment.27 Hypertension diminishes pain perception, and the electrical stimulation of vagal afferent nerves (cardiopulmonary baroreceptors) suppresses nociceptive responses. In addition, both a pharmacological elevation of blood pressure and vascular volume expansion produce anti-nociception.28 Autonomic reactions Autonomic reactions, such as tachycardia, hypertension, sweating and lacrimation, have usually been regarded as signs of nociception or inadequate analgesia, heart rate being less consistent than blood pressure response. Isoflurane used as a sole agent is unable to suppress haemodynamic reactions (blood pressure and heart rate) to painful stimuli. The lack of motor response is not an accurate predictor of the ability of an agent to depress haemodynamic reactions29, but haemodynamic responses after noxious stimulation such as laryngoscopy or tracheal intubation are still considered to be the responses which are easiest to interpret during anaesthesia.30 Motor or haemodynamic responses to nociceptive stimuli could, a posteriori, serve to adapt the dosage of hypnotic or analgesic agents, and heart rate variations have been used to automatically amend remifentanil target-controlled infusion during general anaesthesia.31 Tentative measures for standardisation have been proposed by Evans, using the PRST (blood Pressure, heart Rate, Sweating, Tears) score of responsiveness (Table 1). Table 1. Evans' PRST score. Clinical signs Conditions Score Systolic arterial pressure (mmHg) <Control+15 0 <Control+30 1 >Control+30 2 Heart rate (beats per minute) <Control+15 0 <Control+30 1 >Control+30 2 Sweating None 0 Skin moist to touch 1 Visible beads of sweat 2 Tears No excess of tears in open eye 0 Excess of tears in open eye 1 Tears overflow closed eye 2 Stimulation of the sympathetic system in response to noxious stimulus is, however, not always the case. Parasympathetic stimulation can occur, with opposite responses (Table 2). Table 2. Responses of major organs to autonomic nerve impulses. Organ Sympathetic stimulation Parasympathetic stimulation Heart Increased heart rate β1 (and β2) Decreased heart rate Increased force of contraction β1 (and β2) Decreased force of contraction Increased conduction velocity Decreased conduction velocity Arteries Constriction (α1) Dilatation Dilatation (β2) Veins Constriction (α1) Dilatation (β2) Lungs Bronchial muscle relaxation (β2) Bronchial muscle contraction Increased bronchial gland secretions Eye Dilatation of pupil (α) Constriction of pupil Contraction of sphincters (α) Increased lacrimal gland secretions Liver Glycogenolysis (β2 and α) Glycogen synthesis Gluconeogenesis (β2 and α) Lipolysis (β2 and α) Kidney Renin secretion (β2) Bladder Detrusor relaxation (β2) Detrusor contraction Contraction of sphincter (α) Relaxation of sphincter Uterus Contraction of pregnant uterus (α) Relaxation of pregnant and non-pregnant uterus (β2) Submandibular and parotid glands Viscous salivary secretions (α) Watery salivary secretions Different types of pain can lead to particular reactions. For example, the mesenteric Pacinian corpuscle is the baroreceptor that probably initiates the vasomotor reflexes in skin and muscle32 during abdominal pain. Chronotropic and inotropic responses to the noxious stimulation caused by laryngoscopy or surgical stimulation can be effectively suppressed by beta-receptor blockade33, and esmolol leads to analgesia and a reduction in cardiovascular responses to pain in the non-sedated rat.34 Esmolol does not attenuate the heart rate response to sternotomy but does attenuate the increase in blood pressure in patients receiving chronic beta-blocker therapy.35 Perioperative esmolol administration during anaesthesia reduced the intraoperative use of isoflurane and fentanyl by 25%, decreased haemodynamic responses and reduced morphine consumption by 30% for the first 3 postoperative days in patients undergoing a hysterectomy.36 Vagal afferent nerves are thought to mediate autonomic responses evoked by noxious mechanical or chemical oesophageal stimuli, and participate in the perception of pain originating from the oesophagus. The fibres involved in this mechanism include both A and C fibres.37 Sesay et al have evaluated electrocardiographic (ECG) spectral analysis during surgery on the cerebellopontine angle. Vagal reactions were defined as a decrease in heart rate or an increase in HF of more than 10% of the pre-stimulus value. This monitoring permits the detection of intraoperative vagal reactions earlier than is allowed by the conventional monitoring of heart rate38, as could be seen during a study of hysteroscopy.39 The vagus nerves supply the guinea-pig oesophagus with nociceptors in addition to tension mechanoreceptors.37 Susceptibility to vasovagal reactions after a noxious stimulus may be associated with individual differences in baroreflex sensitivity.40 Monitoring the cardiac autonomic system: heart rate variability Cardiac autonomic function is estimated by heart rate variability measures and is expressed in the time domain as the mean of R–R intervals for normal heart beats and the standard deviation of all normal R–R intervals. The spectral analysis of heart rate variability allows a continuous, non-invasive quantification of cardiac autonomic function, pure vagal activity being assessed by high-frequency power (0.15–0.4 Hz). Low-frequency power (0.04–0.15 Hz) reflects both parasympathetic and sympathetic control. Numerous studies of ischaemic heart disease have used this method, demonstrating the clinical significance of heart rate variability analysis. An acute noxious stimulus appears to produce an increase in respiratory-related sympathetic heart rate control and a significant decrease in respiratory-related parasympathetic control in adults and infants. Stressful events during the heel-prick procedure in newborn infants41 or painful stimuli in children42 could be evaluated by this method. With increasing age, the sympathetic and parasympathetic changes appear to be less intense but more sustained.43 Limitations of this method are artefact detection and the necessity for a long enough period of signal sampling. Wavelet analysis could be helpful with this indication.44 Skin vasomotor reflexes Testing the skin vasomotor reflexes (SVmR) by laser Doppler flowmetry is a recognised method of measuring peripheral dysautonomia and can detect an impairment of the reflex control of fingertip blood flow in both diabetes mellitus and leprosy.45 The reflex control of fingertip blood flow is assessed by measuring the reduction in laser Doppler flowmetry induced by a deep inspiratory gasp, a cold challenge of immersing the contralateral hand in cold water or electrostimulation of the ulnar nerve. Patients with diabetic neuropathy had resting laser Doppler flowmetry levels significantly lower than those of the uncomplicated group and showed a substantial impairment of both the inspiratory gasp and cold challenge reflexes.46 A sympathetic vasoconstrictor reflex is induced by noxious stimulation: laryngoscopy alone and intubation with laryngoscopy significantly reduced skin blood flow.47 Shimoda et al evaluated SVmR in response to laryngoscopy. A decrease in SVmR amplitude to less than 0.1 u before laryngoscopy is associated with blood pressure stability. SVmR amplitude and systolic blood pressure changes showed a significant linear correlation.48 SVmR is also useful to estimate objectively the level of somatosensory block induced by regional anaesthesia.49 and 50 Shimoda et al demonstrated that the level of current that induced the SVmR was proportional to the depth of anaesthesia induced by sevoflurane, and that the duration of electrostimulation (i.e. painful increase) was correlated to the magnitude of the SVmR.51 Thus, the SVmR could be helpful in the objective assessment of nociception and anti-nociceptive effects in individual cases. These authors also investigated the SVmR and haemodynamic responses to the insertion of an intubating laryngeal mask airway and found that the most stressful period was removal of the airway.52 Nakahara et al determined the MAC of anaesthetic that blocked the SVmR to surgical incision (MACBVR) for sevoflurane in 37 patients.53 They found that the MACBVR contribution to the total anaesthetic MAC multiple was 1.75 MAC for sevoflurane alone and 1.43 MAC when 50% nitrous oxide was used. There was no relationship between the amplitude of the reduction in skin blood flow and any changes in haemodynamic variables. Owing to its resistance to chronic ischaemia, the SVmR is preserved in chronically ischaemic limbs with non-diabetic, atherosclerotic peripheral arterial disease.54 Neuropeptide Y participates in sympathetically mediated cutaneous vasoconstriction.55 Owing, however, to the cost of the device to measure its level, this technique is used only in research. Plethysmography Plethysmogram amplitude Sustained pinching of the interdigital webs of the hands of human volunteers induced a tonic reflex vasoconstriction in the stimulated hand with a rather slow adaptation rate and no signs of habituation between trials. Step increases in the pinching force in the course of a stimulus were reflected by a decrease in amplitude of the plethysmogram.56 This reflex occurred at a spinal level but could be inhibited by the cerebral hemispheres.57 Skin incision is followed by a clear sympathetic vasoconstrictor response in the plethysmographic signal, and suppression of the photoplethysmographic pulse wave reflex to a nociceptive stimulus has also been found to predict a reduced haemodynamic response to tracheal intubation.58 The pulse wave reflex may be a better predictor than other variables. In another study, the best variables for logistic regression classification in movers versus non-movers at incision appeared to be response entropy, instant RR and plethysmogram notch amplitude. Plethysmogram notch amplitude was measured as the distance from the baseline to the lowest value of the notch (Figure 1).59 Nevertheless, arterial pressure was not incorporated into the variables studied. (20K) Figure 1. Parameters measured from the pulse plethysmography waveform. Pulse transit time PTT was originally measured by recording the time interval between the passage of the arterial pulse wave at two consecutive sites. More recently, for ease of measurement, the electrocardiographic R or Q wave has been used as the starting point as it approximately corresponds to the opening of the aortic valve. This ‘new’ pulse transit time (rPTT), the interval between ventricular electrical activity and the arrival of a peripheral pulse waveform, has been used to detect changes in autonomic tone and in inspiratory effort. Noxious stimulation can affect this parameter: during anaesthesia, rPTT decreased by an average of 43±25 ms in response to endotracheal intubation but did not vary in response to the insertion of laryngeal mask airway or to a surgical stimulus.60 This measure does not seem suitable, but further studies are needed. The major problem with SVmR and plethysmography-derived measures is that skin blood flow is profoundly influenced by not only pathological states, but also thermoregulatory state, age and emotional stress.61, 62 and 63 Pupil Iris activity reflects physiological reactions to different sensory stimuli, resulting in a variation in pupil size. As such, pupillometry is a method that can provide valuable data concerning the functioning of the autonomous nervous system.64 Pupil size reflects the interaction between the sympathetic and parasympathetic divisions of the autonomic nervous system and can be used to evaluate brainstem function in comatose patients.65 Noxious stimulation and the cold pressure test dilate the pupil—pupillary reflex dilatation (PRD)—in both unanaesthetised and anaesthetised humans.66 In the absence of anaesthesia, dilatation is primarily mediated by the sympathetic nervous system. In contrast, under anaesthesia, pupillary dilatation in response to noxious stimulation or desflurane step-up is mediated principally by inhibition of the midbrain parasympathetic nucleus, although the exact mechanism remains unknown.67 PRD is not present in organ donors (Yang). In addition, esmolol does not block PRD in anaesthetised volunteers.68 Pupillary size and reactivity have long been a critical component of the clinical assessment of patients with or without neurological disorders.69 Neuromuscular blocking drugs do not alter the pupillary light reflex.70 Infrared pupillary scans have been used extensively as an objective measure of pupillary reflexes during pharmacological studies on human subjects.71 Women show greater pupillary dilatation than men, this gender difference in pain perception being beyond voluntary control and reflecting low-level sensory and/or affective components of pain.11 Pupillometry has served to assess the bioavailability of rectal and oral methadone in healthy subjects72, as well as, for example, the influence of age or cytochrome P4503A activity on the acute disposition and effects of oral transmucosal fentanyl citrate.73 and 74 Pupillometry is also able to quantify the extent and time course of the effects of morphine-6-glucuronide.75 Similarly, the pharmacodynamics of epidural alfentanil, fentanyl and sufentanil have been studied with this method.76 and 77 Dynamic pupillometry with automatic recording has recently been developed.78 and 79 PRD is measured using an ophthalmic ultrasound biomicroscope (Oasis Colvard Pupillometer) or video-based pupillometer (Procyon video pupillometer, FIT 2000, videoalgoscan). The pupillary response to noxious stimulation induced by electrical fingertip stimulation was investigated in volunteers by Chapman et al.80 These authors found that PRD began at 0.33 seconds and peaked at 1.25 seconds after the stimulus. PRD increased significantly in peak amplitude as the intensity of the stimulus increased. Larson et al showed that alfentanil exponentially impaired the PRD, decreasing the maximum response amplitude from 5 mm at 0 ng/ml, to 1.0 mm at 50 ng/ml, and to 0.2 mm at 100 ng/ml.81 In contrast, alfentanil administration had no effect on the pupillary light reflex. Dilatation of the pupil in response to a noxious stimulus is a measure of opioid effect, and this stimulus-induced pupillary dilatation may be used to evaluate the analgesic component of a combined volatile and opioid anaesthetic. The relative variations of PRD (+233%) are more sensitive than those of heart rate (+19%) or arterial pressure (+13%) after an electrical stimulus (65–70 mA, 100 Hz) has been applied to the skin of the abdominal wall.68 During anaesthesia, PRD allows an estimation of the sensory level during combined general/epidural anaesthesia in adults.82 The supraspinal effects of epidural fentanyl can be assessed during general anaesthesia using infrared pupillometry, maximum suppression being 70±15% for the epidural route and 96±3% for the intravenous route.83 In children, a PRD of 0.2 mm is sensitive to the loss of analgesia.84 PRD during anaesthesia is not initiated by slowly conducting C fibres, and fentanyl at 3 μg/kg depresses the reflex.85 During propofol anaesthesia in healthy patients, the fall in PRD is a better measure of the progressive increase in effect of a remifentanil concentration up to 5 ng/ml than are haemodynamic measures or the bispectral index (BIS). Pupil dilatation in response to 100 Hz tetanic stimulation decreased progressively from 1.55 (0.72) to 0.01 (0.03) mm as remifentanil concentration increases.86 Similar responses have been found also in children by Constant et al.87 Quantitative pupillary measurements can be reliably obtained during anaesthesia with newer pupillometers. Continuous improvements are seen in the flexibility and recording capacity of pupillometers, and they are used in an increasing number of medical fields, including anaesthesiology. The limitations of this method are that droperidol and metoclopramide constrict the pupil and block the pupillary dilatation brought about by nociceptive stimuli, whereas ondansetron does not. Larson recommends that when pupillary diameter measurements are used to gauge opioid levels during experimental conditions or during surgical anaesthesia, antiemetic medication acting on the dopamine D2 receptor should be avoided.88 Clonidine also modifies the central norepinephric control of pupillary function.89 Autonomic neuropathies and spinocerebellar degeneration syndromes are strongly associated with pupillary abnormality, both at rest and in tonic conditions, and may disturb monitoring. Ocular microtremor Ocular microtremor is a physiological tremor whose frequency is related to the functional status of the brainstem. It is suppressed by propofol and sevoflurane in a dose-dependent manner. Sevoflurane and ocular microtremor accurately predict response to verbal command.90 Ocular microtremor may be a useful monitor of depth of hypnosis, but further studies are needed despite encouraging results in the evaluation of preoperative analgesia.91 Spontaneous EEG The effects of noxious stimulation on the EEG have long been studied to monitor cerebral function.92 The basic EEG responses to noxious surgical stimulation have not been clearly defined, which has been a major factor limiting the clinical use of the EEG to monitor anaesthesia. Bispectral index The BIS is a statistical index involving the weighted average of three subparameters that analyse the phase and frequency relations between the component frequencies in the EEG.93 It changes with increasing concentration of anaesthetic agents and is correlated with sedation scales. The BIS correlates well with the hypnotic component of anaesthesia but predicts movement in response to surgical stimulation less reliably, especially when different combinations of hypnotic and analgesic drugs are used. Use of the BIS has been shown to prevent awareness in at-risk patients.94 Early studies with the BIS show that it could be a useful predictor of whether patients will move in response to skin incision during anaesthesia with isoflurane/oxygen or propofol/nitrous oxide and no opioid.95 and 96 Leslie et al97 have compared several parameters in 10 propofol-anaesthetised volunteers and determined their prediction probability of movement. The BIS (PK=0.86), 95% spectral edge frequency (PK=0.81), pupillary reflex amplitude (PK=0.74) and systolic arterial blood pressure (PK=0.78) did not differ significantly from those of a modelled propofol effect-site concentration (PK=0.76). In a study of 60 unpremedicated adults98, a BIS of 60 separated patients responding to laryngeal mask airway insertion from non-responders (P=0.006), with a sensitivity of 68% and a specificity of 70%. Movement response was not predicted by cardiovascular changes. Sebel et al, in a multicentre study, pointed out that, when opioid analgesics were used, the correlation to patient movement became much less significant, so that patients with apparently ‘light’ EEG profiles could not move or otherwise respond to incision. Therefore, the adjunctive use of opioid analgesics confounds the use of BIS as a measure of anaesthetic adequacy when movement responses to skin incision99 or to another noxious test100 are used. BIS and sevoflurane end-tidal concentration are reliable guides to the depth of sedation, with prediction probability values of 0.966 and 0.945, respectively, but not to the adequacy of anaesthesia for preventing movement.101 In a same way, Doi et al102 have shown that the auditory evoked potential (AEP) index discriminated between movers and non-movers with a prediction probability of 0.872. BIS, spectral edge frequency and median frequency could not predict movement at laryngeal mask airway insertion in patients anaesthetised with propofol and alfentanil. The addition of remifentanil to propofol affected the BIS only when a painful stimulus was applied.103 Moreover, remifentanil attenuated or abolished increases in BIS and MAP after tracheal intubation in a comparable dose-dependent fashion. In another study with sevoflurane104, the prediction probability values for AEP index, BIS and sevoflurane concentration for sedation score were 0.820, 0.805 and 0.870, respectively, indicating a high predictive performance for depth of sedation. AEP index and sevoflurane concentration successfully predicted movement after skin (prediction probability 0.910 and 0.857, respectively), whereas BIS did not (prediction probability 0.537). Despite these limitations, BIS might be a useful clinical monitor for predicting patient movement to command during the intraoperative wake-up test in scoliosis surgery105, particularly when controlled hypotension is used and haemodynamic responses to the emergence of anaesthesia are blunted. There are, however, various limitations of the BIS. Vivien et al pointed out the fact that the fall in BIS following the administration of myorelaxant was significantly correlated to the BIS.106 During fentanyl-induced muscular rigidity, BIS recordings reflect EMG variations. When assessing BIS in the absence of neuromuscular blockade, it is necessary to evaluate the effect of the electromyelogram (EMG) on the BIS before making conclusions about depth of sedation. Fentanyl-induced rigidity appears to be a dose-related phenomenon that an EMG variable of BIS 3.4 is able to quantify.107 It must be borne in mind that BIS is primarily a sedation monitor. Entropy Entropy is a quantitative measure used to determine the disorder or randomness in a closed system, in the sense of thermodynamic/metabolic processes or the increasing molecular disorder in a structure, according to Boltzmann's definition of entropy (S) S=k ln(Ω). The second law of thermodynamics states that the entropy (and disorder) increases as time moves forward. Shannon has extended this concept to information theory and defines entropy in terms of a discrete random event x, with possible states 1,…,n as: H(x)=−Sumi(p(i)log(p(i)). There are multiple ways in which to compute the entropy of a signal: in a time domain, as approximate entropy108 and 109 or as Shannon entropy.110 In the frequency domain, spectral entropy may be computed; this is the case for the Datex-Ohmeda Entropy Module, a new EEG monitor designed to measure depth of anaesthesia.111 The monitor calculates a ‘state entropy’, computed over the frequency range 0.8–32 Hz, and a ‘response entropy’, computed over the frequency range 0.8–47 Hz. The difference between the response and state entropies is a reflection of the high-frequency activity of the EEG, and includes by nature some EMG-frequency components. Some studies with this monitor have now been published. It appears that it has the same lack of sensibility as the BIS when analgesics drugs are used, for example with ketamine112 or nitrous oxide.113 An elevated difference between response entropy and state entropy is related to a significant increase in state entropy, blood pressure and heart rate, response entropy during painful stimulation is seen more often in patients anaesthetised with 0.8% compared with 1.4% isoflurane. Response entropy more probably reflects the frontal EMG and may be useful to identify inadequate anaesthesia and patient arousal during painful stimulation.114 Vanluchene et al115 compared state entropy, response entropy and BIS when measuring loss of response to verbal command (LOR(verbal)) and noxious stimulation (LOR(noxious)) during propofol infusion with and without remifentanil. BIS, state entropy and response entropy all detected LOR(verbal) accurately, but BIS performed better at 100% sensitivity. The sensitivity/specificity for the detection of LOR(verbal) decreased for all methods with increasing Ce(REMI). LOR(noxious) was poorly described by all measures. Future studies are needed to elucidate the role of response entropy in terms of analgesia monitoring. Evoked EEG Animal and human cerebral evoked potentials have been employed for years in pain research to describe pain perception physiology and to test the effectiveness of various analgesics.116 and 117 More recently, positron emission tomography has revealed significant changes in pain-evoked activity within multiple cerebral regions, particularly the anterior cingulate cortex.118 Subdivision of the anterior cingulate cortex into an anterior non-specific attention/arousal system and a posterior pain system explain the interaction between alertness and pain.119 Mid-latency AEPs are small changes noted on the EEG that are caused by discrete auditory stimuli. AEPs are more sensitive to pain stimuli than are spectral features of the spontaneous EEG120 or BIS.102 The A-Line Auditory Evoked Index (AAI) is a unique device commercially available for depth of anaesthesia monitoring. Values of the index range between 0 and 100, but there is a wide variation in the awake values and a considerable overlap of AAI values between consciousness and unconsciousness, suggesting that further improvement of the AAI system is required.121 and 122 Unlike AEPs, because of the variability in latency and the difficulties of repeating stimulation, somatosensory evoked cerebral potentials are analysed by calculating the spectral power in selected frequency bands and frequency percentiles from the spontaneous EEG segment preceding each somatosensory stimulus. Late cortical somatosensory evoked potentials response parameters are calculated from the respective post-stimulus EEG segments. Spectral analysis of the late cerebral (later than 80 milliseconds) components of the potential evoked by painful somatosensory stimuli reveals a stimulus-induced increase of power in the low frequencies—delta and theta. The pre-stimulus:post-stimulus relationship of the delta waves was found to be the most sensitive measure for monitoring the cerebral bioavailability of meperidine.123 Under halothane anaesthesia, late somatosensory evoked potentials and haemodynamic responses in response to painful electrical stimuli are abolished by fentanyl.124 The same authors showed that the analgesic effect of low-dose ketamine (0.25 and 0.5 mg/kg) could be quantified by somatosensory evoked potentials, especially by a dose-dependent decrease of the long-latency N150-P250 somatosensory-evoked late cortical response.125 Laser-evoked potentials are nociceptive-related brain responses to activation of the cutaneous nociceptors by laser radiant heat stimuli. The cost of the technique is the major limitation to its development. Monitoring analgesic administration The computer administration of opioids by target-controlled infusion contributes to the monitoring of analgesia.126 and 127 Real-time displays of intravenous anaesthetic concentrations and effects could significantly enhance intraoperative clinical decision-making by a visualisation of pharmacodynamic relationship between hypnotics and analgesics.128 Titration of opioids during noxious events The majority of clinical studies have focused on the BIS. Brocas et al showed that an alfentanil bolus of 15 μg/kg markedly reduced the increase in BIS values, blood pressure and heart rate observed immediately after tracheal suction, whereas there are differences in Ramsay scores.129 Godet et al showed that maintenance of anaesthesia predominantly with propofol and a low dose of remifentanil, administered in accordance to the BIS, was associated with a greater stability in perioperative haemodynamics.130 Likewise, sufentanil effect-site concentrations adjusted on BIS values and variations could achieve good haemodynamic tolerance.127 In cardiac patients, titration of propofol using the BIS allows a significant reduction in propofol consumption, with only minor effects on the stress response in these conditions.131 Considerations of stability Analgesia is a stable state seen both during and after a noxious stimulus. One of the questions of importance here is the definition of stability. For example, a system is stable if it can maintain equilibrium after stimulation, and adequate analgesia could be defined in terms of resistance to change. In control theory, stability characterises the reaction of a dynamic system to external influences. Likewise, haemodynamic stability is often defined by a lack of variation between 20% under or upper reference heart rate or arterial pressure. This percentage is guided by experience and can be changed if a more stable state is required. Absolute or relative percentages of variation, coefficients of variation, standard deviations and ranges are parameters available to describe stability. Variations in statistical significance are not always of great clinical use. Analgesia is a temporal state and must always be topped up against a background of duration and intensity of stimulation. Conclusion If information collected from the EEG response entropy, heart rate and pulse plethysmography of anaesthetised patients is combined, a significantly improved classification performance (96%) between movers and non-movers to skin incision is achieved compared with discrimination using any single variable alone. This suggests that a combination of information from different sources may be necessary for monitoring the level of nociception during anaesthesia.59 Pupillometry seems to be a promising generalised tool, but we must aware of being too enthusiastic towards it because there are commercially available analgesia monitors who no longer still exist.132 Many candidate signs are available for analgesia monitoring (Table 3). But whatever the latest monitors are like133 and 134, they will never be able to predict whether the depth of analgesia is sufficient for the next painful surgical stimulus: they can only monitor the anaesthetic state at the time of measurement, and the balance between excitation and responsiveness. Anaesthetists must always consider their experience ahead of any technique for monitoring the depth of analgesia. Table 3. Different parameters available for monitoring analgesia. Parameter to be monitored Clinical scales PRST score Sedation scores Effect of pain Sympathetic system Direct microneurography Heart rate variability Spectral analysis of heart rate Low-frequency/high-frequency power ratio Arterial blood pressure Skin vasomotor reflexes: laser Doppler flowmetry Plethysmogram amplitude, notch amplitude Pulse transit time Ventilation Respiratory rate Pupil Pupillary reflex dilatation Brainstem Ocular microtremor Spinal Movement Cerebral Response entropy Auditory evoked potentials Somatosensory evoked potentials Spectral analysis of late cerebral potential components Bispectral index Action of analgesics Plasma concentration Theoretical concentrations with target-controlled infusions Secondary effects: heart rate, respiratory rate Action of anaesthetics End-tidal concentrations of inhaled anaesthetics Theoretical concentrations of intravenous drug Multiparametric approaches are probably the best way to deal with monitoring analgesia.135 Like Kutas and Federmeier136, we could say that a combination of measures—old and new, central and peripheral—will ultimately provide the greatest power to resolve the questions we hope to answer, using all the physiological measures at our disposal, in our quest to understand the nature of the relationship between mind and body, between analgesia and anaesthesia.(Box 1) Research agenda • characterise the mechanisms of pain perception • characterise the mode of action of analgesics • characterise individual variations in and intervariability of events related to noxious stimuli • develop plethysmography-derived and pupillary reflex indices • include the pharmacodynamics of hypnotics/analgesics in EEG automated depth of anaesthesia systems • develop data-fusion systems and multimodal monitoring of analgesia References 1 C. 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Abstract-EMBASE | Abstract-MEDLINE 53 T. Nakahara, S. Yasumoto, Y. Jinnouchi and K. Hano, Concentrations of sevoflurane with and without nitrous oxide to block vasomotor reflexes to incision (MACBVR), Masui 51 (2002), pp. 7–13. Abstract-MEDLINE | Abstract-EMBASE 54 H. Nukada, A.M. van Rij, S.G. Packer and A. Patterson, Preservation of skin vasoconstrictor responses in chronic atherosclerotic peripheral vascular disease, Angiology 49 (1998), pp. 181–188. Abstract-MEDLINE | Abstract-EMBASE 55 D.P. Stephens, A.R. Saad and L.A. Bennett et al., Neuropeptide Y antagonism reduces reflex cutaneous vasoconstriction in humans, American Journal of Physiology, Heart and Circulatory Physiology 287 (2004), pp. H1404–H1409. Abstract-MEDLINE | Abstract-EMBASE | Abstract-Elsevier BIOBASE | Full Text via CrossRef 56 W. Magerl, G. Geldner and H.O. Handwerker, Pain and vascular reflexes in man elicited by prolonged noxious mechano-stimulation, Pain 43 (1990), pp. 219–225. Abstract 57 A.G. Herbaut, J.D. Cole and E.M. Sedgwick, A cerebral hemisphere influence on cutaneous vasomotor reflexes in humans, Journal of Neurology Neurosurgery and Psychiatry 53 (1990), pp. 118–120. Abstract-EMBASE | Abstract-MEDLINE 58 M. Luginbuhl, F. Reichlin and G.H. Sigurdsson et al., Prediction of the haemodynamic response to tracheal intubation: comparison of laser-Doppler skin vasomotor reflex and pulse wave reflex, British Journal of Anaesthesia 89 (2002), pp. 389–397. Abstract-MEDLINE | Full Text via CrossRef 59 E.R. Seitsonen, I.K. Korhonen and M.J. van Gils et al., EEG spectral entropy, heart rate, photoplethysmography and motor responses to skin incision during sevoflurane anaesthesia, Acta Anaesthesiologica Scandinavica 49 (2005), pp. 284–292. Abstract-MEDLINE | Abstract-EMBASE | Abstract-EMBASE | Full Text via CrossRef 60 S. Singham, L. Voss, J. Barnard and J. 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Halonen, Infrared pupillometry in the assessment of autonomic function, Diabetes Research and Clinical Practice 26 (1994), pp. 61–66. Abstract 65 M.D. Larson and I. Muhiudeen, Pupillometric analysis of the ‘absent light reflex’, Archives of Neurology 52 (1995), pp. 369–372. Abstract-MEDLINE | Abstract-EMBASE 66 C. Tassorelli, G. Micieli and V. Osipova et al., Pupillary and cardiovascular responses to the cold-pressor test, Journal of The Autonomic Nervous System 55 (1995), pp. 45–49. SummaryPlus | Full Text + Links | PDF (504 K) 67 M.D. Larson, F. Tayefeh and D.I. Sessler et al., Sympathetic nervous system does not mediate reflex pupillary dilation during desflurane anesthesia, Anesthesiology 85 (1996), pp. 748–754. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 68 M.D. Larson, D.I. Sessler and D.E. Washington et al., Pupillary response to noxious stimulation during isoflurane and propofol anesthesia, Anesthesia and Analgesia 76 (1993), pp. 1072–1078. 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MacKeen et al., Pupillary reflex dilation and skin temperature to assess sensory level during combined general and caudal anesthesia in children, Paediatric Anaesthesia 14 (2004), pp. 768–773. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 85 M.D. Larson, P.D. Berry and J. May et al., Latency of pupillary reflex dilation during general anesthesia, Journal of Applied Physiology 97 (2004), pp. 725–730. Abstract-Elsevier BIOBASE | Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 86 L. Barvais, E. Engelman and J.M. Eba et al., Effect site concentrations of remifentanil and pupil response to noxious stimulation, British Journal of Anaesthesia 91 (2003), pp. 347–352. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 87 I. Constant, M.C. Nghe, P. Richard and I. Murat, Pupillary response to skin incision in children anesthetized with sevoflurane: a comparison with hemodynamic parameters, Anesthesiology 103 (2005) (supplement), p. 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Hello Everyone, Since this has been an ongoing topic of discussion here recently here's a great overview article of the different 'Airway Assessment scales'. Hope This Helps, ACE844 (Best Practice & Research Clinical Anaesthesiology Volume 19 @ Issue 4 , December 2005, Pages 559-579 Difficult Airway Management doi:10.1016/j.bpa.2005.07.004 Copyright © 2005 Elsevier Ltd All rights reserved. 2 Evaluation of the airway and preparation for difficulty Adrian Pearce FRCA, , Consultant Anaesthetist Department of Anaesthesia, Guy's and St Thomas' Hospital, London SE1 9RT, UK Available online 5 December 2005.) Preoperative airway evaluation is essential to consider which is the best method of maintaining and protecting the airway during surgery and whether problems with airway management are likely. In general surgical patients, the prevalence of difficult intubation is low and tests have poor predictive power. This means that the patient may be evaluated as normal but prove to be difficult. The absence of reliable prediction in general surgical patients means that airway strategy holds the key to successful management. Where there are obvious abnormalities in the history, examination or imaging the preoperative evaluation will allow choice of the most appropriate airway strategy which may include preparation of the patient, assembling of alternative airway equipment, advice and help from a more senior or skilled anaesthetist or aid from a surgical colleague or assistant. Definitions and prevalence The publication of the practice guidelines for management of the difficult airway1 by the American Society of Anesthesiologists (ASA) in 1993 was a landmark publication. It contains much good information, but it is unfortunate that only the facemask and tracheal intubation were used in the USA at that time and no mention of supraglottic airways was made. The difficult airway was defined as difficulty with facemask ventilation or tracheal intubation or both. Difficult facemask ventilation Defined initially by the ASA as the inability to maintain oxygen saturations >90% with 100% oxygen by facemask (if saturations were above this value before induction of anaesthesia) or to reverse signs of inadequate ventilation. This is a good definition, but the prevalence of it is unknown although it is rare in general surgical patients. A generally quoted prevalence of failed ventilation and intubation at induction of anaesthesia leading to serious morbidity or death is 1:10 000–1:100 000. A more recent study2 in 1502 patients defined the prevalence of subjective difficulty with facemask ventilation when the anaesthetist ‘considered that the difficulty was clinically relevant and could have lead to potential problems if mask ventilation had to be maintained for a longer time’. The categories used were inability to maintain oxygen saturations >92%, important gas leak, no perceptible chest movement, necessity for 2-handed technique or a change of operator. The prevalence of difficulty (as so defined) was 5% (95% CI 3.9–6.1%). Difficult laryngeal mask ventilation Not defined by the ASA or any other major body, but in research work is defined as the inability within three insertions to place the mask in a satisfactory position to allow clinically adequate ventilation and airway patency. Indices of clinically adequate ventilation are generally delivered (expired) tidal volume >7 ml/kg and leak pressure >15–20 cm H2O. In one study3 of >11 000 patients the failure rate was 0.16%. A similar definition of failure of satisfactory placement within three attempts could be applied to all supraglottic airway devices. Difficult intubation Tracheal intubation may be difficult because of failure to see the glottis by line-of-sight, or due to laryngeal or tracheal distortion or narrowing. The management of these situations is quite different and the term ‘difficult intubation’ is so vague as to be meaningless. A much more appropriate term for difficulty in seeing the glottis by line-of-sight is difficult direct laryngoscopy. The updated ASA practice guidelines4 in 2003 suggested that difficult direct laryngoscopy is when ‘it is not possible to visualise any portion of the vocal cords after multiple attempts at conventional laryngoscopy’. Difficult tracheal intubation is when ‘tracheal intubation requires multiple attempts in the presence or absence of tracheal pathology’. A number of definitions of difficult intubation, sometimes referring specifically to difficult direct laryngoscopy, are used clinically or in research work. They refer to the use of the traditional curved Macintosh or straight blade laryngoscope by an experienced practitioner with at least 2 years full-time experience in anaesthetics. Difficult intubation can be defined in a number of ways. Time taken to achieve intubation The original ASA definition of difficult intubation included a time limit of 10 minutes, a time limit which must include repeated facemask ventilation. A much shorter time limit has been used. One study5 of 1000 patients defined prolonged laryngoscopy if intubation had not been completed within 15 seconds. The prevalence of this was 16%. In another recent study in 700 patients6 looking at the influence of cricoid force on difficulty of intubation a time limit of 30 seconds was used. The prevalence of difficult intubation by this definition was 4% with a median intubation time of 11 seconds. One definition of difficult or failed intubation, which may be used in obstetric anaesthesia, incorporates a time element. Where common practice is to use only one dose of suxamethonium in caesarean section under general anaesthesia, failed intubation is defined as the inability to intubate within one dose of suxamethonium. The prevalence in this particular group of patients7 is approximately 1:300. Number of attempts at direct laryngoscopy The ASA originally defined difficulty by the requirement for more than three attempts at intubation by direct laryngoscopy (or more than 10 minutes). In one large study8 involving 18 205 patients tracheal intubation required more than two attempts at direct laryngoscopy in 1.8%, intubation failed in 0.3% and surgery was postponed in 0.05%. In another study9 of 3325 consecutive patients three or more attempts at direct laryngoscopy were needed in 1.9% and intubation failed by direct laryngoscopy in 0.1%. View at direct laryngoscopy It is common to use the original 4 grades of laryngeal exposure described by Cormack and Lehane10 with Grade 3 (epiglottis only) and Grade 4 (no view of the larynx) being taken as indicating difficult direct laryngoscopy. The standard for description of the laryngeal view is the best view of the larynx with optimal head and neck positioning, optimal blade length and position, optimal external laryngeal manipulation and muscle relaxation (or abolition of glottic reflexes). The application of external laryngeal manipulation is particularly important (and often missed in early studies) reducing the incidence of a Grade 3 or 4 view from 8 to 1.5–2% in general surgical patients. The prevalence of a Grade 3 or 4 view is much higher in ENT patients (5–10%) and may be up to 15–20% in patients with cervical spine disease. Other gradings have been promoted, particularly a 5-grade modified Cormack and Lehane11 which splits Grade 2 into 2A (partial view of the vocal cords) and 2B (only the arytenoids and epiglottis seen). In a study12 of 605 patients, prevalence of Grade 2B was 3.3%, Grade 3 1.6% and Grade 4 0.2%. In the same study, difficult intubation was defined also as requiring more than one intubation attempt or the use of intubation aids, such as the gum elastic bougie and specialist blades. By this definition 65% of Grade 2B patients were difficult, 80% of Grade 3 and the only Grade 4 view was difficult to intubate. Another scale13 uses the percentage of glottic opening (POGO), but is hampered by the fact that the POGO scale must incorporate an estimate of how much glottic opening cannot be visualised. Requirement for specialised equipment Difficulty has been defined in a number of studies by the requirement to use a device other than a direct laryngoscope. This has some practical application because alternative devices such as the intubating fibrescope or alternative blades are commonly in a central location outside an individual operating room. There is no agreement as to what constitutes additional equipment. The introducer (gum-elastic bougie) may be seen as part of normal direct laryngoscopy or a specialised technique. Intubation difficulty scale The intubation difficulty scale (IDS) was proposed in 199714 and incorporates seven variables (Table 1) to describe the ease/difficulty of a particular intubation by direct laryngoscopy. The sum of each variable produces the IDS score allowing a gradation of intubation from easy through to impossible, rather than a simple difficult/not difficult definition. The first three (N1-3) variables have no upper limit, the fourth variable (N4) is glottic exposure according to the Cormack and Lehane four grades minus one. A Grade 1 view is accorded zero points and a Grade 4 view three points. Successful blind nasotracheal intubation scores 0. The glottic exposure is evaluated during the first attempt by the first operator. The last three variables (N5-7) are scored either 0 or 1. An IDS of 0 indicates intubation without difficulty and there is no upper limit. The cut-off to define difficult intubation is arbitrary but a value of five has been used in more than one study. In a prospective study15 of 1171 patients an IDS=0 was found in 55% patients with IDS >5 occurring in 8% patients. Table 1. The intubation difficulty scale.14 N1 Number of attempts >1 N2 Number of operators >1 N3 Number of alternative techniques N4 Cormack Grade—1 N5 Lifting force required (normal 0 or increased 1) N6 Laryngeal pressure (not applied 0 or applied 1) N7 Vocal cord mobility (abduction 0 or adduction 1) Benumof16 proposed two ‘very good’ uses of the scale. Firstly, in communicating the total intubating difficulty for a given patient to the next care-giver, and in research of the predictive power of a specific variable in identical patient groups. It should be noted that a particular score may be obtained through differing problems and any score, on its own, is not diagnostic or proscriptive. This means that the scale is only of practical use if the score for each of the seven variables is recorded and transmitted to the next anaesthetist. Can't-ventilate-can't-intubate (CVCI) A term introduced initially when the only airway techniques were facemask ventilation and tracheal intubation, with CVCI indicating failed facemask ventilation and failed intubation. Hypoxaemia and death occur unless emergency transtracheal oxygenation is successful. It is clear that in a number of situations when facemask ventilation fails, the laryngeal mask may provide a satisfactory airway. A better term which indicates failed facemask, failed laryngeal mask and failed intubation is can't-intubate-can't-oxygenate (CICO). It is rare in elective surgical patients. Clinical evaluation Evaluation of the airway allows adoption of a sensible strategy and a number of questions need to be answered17 and 18 by the anaesthetist when seeing a patient preoperatively; • Is airway management necessary? • Which airway device do I need to provide adequate protection and maintenance of the airway? • Will facemask/laryngeal mask ventilation be possible after induction of anaesthesia? • Will direct laryngoscopy and tracheal intubation be difficult? • Is there an aspiration risk? • Is the cricothyroid membrane available for emergency oxygenation if needed? • Will the patient tolerate a period of apnoea? It can be seen that prediction of difficulty is only part of the preoperative evaluation and the end-point of evaluation is adoption of one of a number of strategies, which will be discussed later. Prediction of difficult airway management With regard to prediction of difficulty, a number of individual tests, combination of tests, scales, scores and indices have been described. It is appropriate initially to delineate the terms used to describe the accuracy or predictive power of the tests. It is easy to be seduced by the favourable mathematical terms selected by the authors when, in fact, the test is not very good. Yentis19 describes the problems with many studies looking at prediction of difficult airway management, is essential reading and provides a good reference base. Descriptive terms of prediction Four terms provide the information needed to analyse the usefulness of a predictive test and to aid explanation the term ‘difficult patient’ indicates a ‘difficult-to-intubate’ patient and ‘normal’ patient indicates a ‘not-difficult-to-intubate’ patient. Sensitivity Test sensitivity is a measure of whether it identifies correctly the difficult patients as being difficult. A test sensitivity of 80% indicates that 80% of the difficult patients will be identified correctly as difficult, and 20% will be missed and classified as not-difficult or normal. A test sensitivity of 100% is ideal. Specificity Specificity of a test identifies that a normal patient is normal. A specificity of 80% indicates that 80% of normal patients will be correctly identified as normal, but 20% of normal patients will be identified incorrectly as difficult. A test specificity of 100% is ideal. The sensitivity and specificity of described tests are substantially below the ideal value of 100% (Table 2). The prevalence of difficult intubation is low with a Grade 3 laryngeal view being found in only 2% general surgical patients. High test specificity is needed to identify as normal the 98% patients who are normal. Table 2. Predictive ability of common tests (from Yentis19). Test Sensitivity (%) Specificity (%) PPV (%) Mallampati (original) 42–60 81–89 4–21 Mallampati (modified) 65–81 66–82 8–9 Thyromental 65–91 81–82 8–15 Sternomental 82 89 27 Wilson score 42–55 86–92 6–9 Mouth opening 26–47 94–95 7–25 Jaw protrusion 17–26 95–96 5–21 Positive predictive value (PPV) The positive predictive value is the percentage who are true difficult intubations out of all those predicted by the test to be difficult. If the test predicts that 20 patients will be difficult, but only five are found to be actually difficult, the PPV is 25%. The PPV is a useful idea but one limitation, when comparing tests from various studies, is that it is dependent on the prevalence of difficult intubation in the study group. This is an important point and is illustrated by a calculation (Table 3). Table 3. Calculation of positive predictive value. •Consider 1000 patients with 5% prevalence of difficult intubation •There are 50 difficult and 950 normal patients •Use predictive test with sensitivity 80% and specificity 80% •Sensitivity labels 40 patients as difficult (and misses 10 of the difficult patients) •Specificity labels 760 patients as normal and (erroneously) 190 as difficult •PPV=40 (true difficult)/40+190 (predicted to be difficult)=17% •If the prevalence of difficult intubation is 10%, and the same test is used •PPV=80/80+180=30% •PPV is influenced by the prevalence of difficult intubation in the study group Likelihood ratio The likelihood ratio (LR) is an extremely useful term and can be calculated within seconds by the reader using only the sensitivity and specificity. It is not dependent, therefore, on prevalence of difficult intubation. The LR is the chance of a positive test if the person is difficult, divided by the chance of a positive test if the patient is normal. The LR is the sensitivity/1−specificity, so that if a test has sensitivity of 80% and specificity of 80% the LR=80/100−80=4. The LR can be seen as a multiplication or amplification factor that links the pre-test probability to the post-test probability of difficult intubation. The nomogram (Figure 1) allows for calculation of the probability, if the test is positive, of the patient being difficult to intubate. The pre-test probability (left-hand scale) is the prevalence of difficult intubation in the population—about 2% in the general surgical population. If the test has an LR of 4, the post-test probability is about 7% indicating that if the test is positive there is only an 7% chance that the patient will be difficult to intubate—making it unlikely that the test will influence management. A higher prevalence and the same LR will give a higher post-test probability indicating that the higher the prevalence of a condition the easier it is to predict. Figure 1. Nomogram for likelihood ratio. As can be seen from Figure 1, the LR is not a strict mathematical multiplication factor so that a pre-test probability of 10% and LR of five gives rise to a post-test probability of 35% (and not 50%). The function which allows strict multiplication is ‘odds’ and not ‘probability’, but probabilities are easier to interpret. Receiver operating characteristic curves (ROC) ROCs provide a means of determining the ‘best’ predictive score and are constructed by plotting the sensitivity (vertical axis) against 1-specificity. The best predictive score, or the better of two tests, is the one which has the greatest area under the curve. An example (Figure 2) is taken from a study which developed a risk index score with a maximum score of 48. The ROC curve shows that 11 points is the best cut-off. The axes of a ROC curve are those required to calculate the likelihood ratio and this can be determined for any point on the curve. In Figure 2, a score of 11 has a LR of about nine. Figure 2. Receiver operating characteristic curve. Reproduced from Arne´, Descoins, Fusciardi et al (1998)49, with permission Factors associated with difficulty A number of factors with some association with difficult airway management have been described (Table 4). The factors are derived from the previous anaesthetic history, history of the current or past disease process, concurrent medical disease, examination and specific tests. The association may be strong or weak, derived from studies or experience and may indicate difficulty with intubation or mask ventilation. Table 4. Factors with some association with difficult airway management. •Previous noted difficulties •Male, age >40–59, obesity •Diabetes, acromegaly, rheumatoid arthritis, obstructive sleep apnoea •Trauma, burn, swelling, infection, haematoma of the mouth, tongue, pharynx, larynx, trachea or neck •Large tongue, receding jaw, high arched palate, prominent upper incisors, short thick neck, large breasts, microstomia, fixed or ‘high’larynx •Mouth opening, 2–3 cm, jaw protrusion class C, Mallampati class 3 or 4, thyromental distance <6 cm, reduced head/neck mobility •Voice change, shortness of breath, difficulty swallowing, choking, stridor, inability to lie flat, drooling of saliva Difficult mask ventilation Prediction of this is particularly important because of the seriousness of failed ventilation, but the prevalence is so low in general surgical patients that no test is accurate. Common reasons which lead anaesthetists to predict difficult facemask ventilation are signs and symptoms of airway obstruction, known pathology around the airway including anterior mediastinal masses, facial deformity precluding a tight mask fit and a rigid or immobilised neck. In Langeron's study2 five factors were associated with difficult facemask ventilation (as defined in the study)—age>55, BMI>26, edentulous, history of snoring and presence of facial hair. The presence of any two factors had a sensitivity 72%, specificity 73% giving an LR of 2.5. Laryngeal mask insertion may be difficult with limited mouth opening, a high arched or defective palate, large oropharyngeal masses and the device is not designed to maintain the airway in the presence of laryngeal or tracheal pathology. History A history of difficult airway management should be considered a strong predictor of problems, unless the difficulty was related to a specific reversible disease process at the time—for example a dental abscess. The history may be available from previous anaesthetic records, the hospital notes, a letter accompanying the patient, verbal recollections from the patient or a Medic-Alert bracelet. A presumptive history of difficulty is indicated by bruised lips, loss or chipping of front teeth during a previous anaesthetic, an unexpected admission to critical care unit or a pharyngeal, oesophageal or tracheal perforation. Signs or symptoms of airway obstruction A disease process which affects the head neck or mediastinum and causes distortion or narrowing of the airway ranks highly. Both facemask ventilation and intubation may be difficult. Airway narrowing may be suggested by a history of difficulty with breathing, requirement to adopt a sitting or lateral position to facilitate breathing, stridor (noisy breathing), dysphonia, dysphagia or increased work of breathing. In chronic obstruction the hypertrophy of the intercostal muscle mass means that shortness of breath may not be present even though the airway is narrowed to 3–4 mm. Wherever possible the airway should be imaged by flexible nasendoscopy of the pharynx and larynx, X-ray, CT or MR (Figure 3) scans or flow-volume loops. Figure 3. MR scan showing base of tongue tumour Mouth opening and jaw protrusion Limited mouth opening is another important factor. An inter-incisor distance less than 5 cm or 2–3 fingerbreadths (fb) may be indicative of difficult direct laryngoscopy, and less than 1 fb or 1.5 cm will impair insertion of a laryngeal mask and laryngoscope. A distance of 2 cm is required to insert an intubating laryngeal mask. Maximal mouth opening is influenced20 by the degree of atlanto-occipital neck extension. In the Australian Critical Incident Monitoring Study21, the four variables associated with difficult intubation were limited mouth opening, obesity, limited neck extension and lack of trained assistant. Jaw protrusion (also termed prognathism or subluxation) is the ability to slide the lower incisors in front of the upper ones and may be classed as A, B or C. Class A indicates that the lower teeth may be placed in front of the top teeth, Class B that they may be placed in line with the top teeth and Class C that they cannot reach the top teeth. Class C is rare in general surgical patients, but predictive. Limited mouth opening together with limited jaw protrusion often ranks highly in airway scores (see Wilson Risk Sum and Arné). An allied test to jaw protrusion is the upper lip bite (ULBT)22 which is defined as Class 1 the lower incisors can bite above the vermilion border of the upper lip, Class 2 the lower incisors can bite the vermilion border of the upper lip and Class 3 that they are unable to bite the top lip. In a study of 300 patients (excluding edentulous patients, those who could not open the mouth or with limited cervical movement and those with laryngeal masses) the sensitivity was 76%, specificity 88% giving an LR of 6.5. In the same study the modified Mallampati performed more poorly with an LR of <3. Mallampati The Mallampati test has become popular but is no better or worse than many other tests. There is considerable inter-observer variation and confusion as to the number of classes. It is commonly performed in the seated position with maximal mouth opening and tongue protrusion, but without vocalisation. One study23 promoted vocalisation within the test. Mallampati24 described three classes and it was Samsoon and Young25 who added the fourth class with Class 3 indicating the tongue against the soft palate and Class 4 the tongue against the hard palate. The four-class test is often referred to as the modified Mallampati. The LR of the test in general surgical patients is from 1.5 to 6. The summary of a recent study26 of 1956 patients states the current position with this test ‘.. the Mallampati score by itself is insufficient for predicting difficult endotracheal intubation’. There is no scientific reason, in general surgical patients, for an isolated Mallampati 3 to influence anaesthetic management. Thyromental or sternomental distance Various measurements have been evaluated with the thyromental gaining most credibility although the LR is low. Limits below which the tests are suggested to provide some prediction of difficult intubation are thyromental 6 cm or 3 fb and sternomental 13.5 cm. The original sternomental study27 described the test as the distance between the mentum and sternum with the head fully extended on the neck and the mouth closed. In 523 obstetric patients, the prevalence of a Grade 3 or 4 laryngeal view was 3.5%. The predictive power of a threshold value of 13.5 cm or less was sensitivity 67% and specificity 71% giving an LR of 2. An analysis of ROC curves incorporating confidence intervals led Farmery28 to suggest that as a predictor of difficult laryngoscopy the test has a ‘diagnostic accuracy approaching worthlessness’. Obesity There is no clear consensus as to whether obesity per se should be regarded as a risk factor and reasons for discrepancy may be the end-point used to define difficulty and methodological errors. One study29 examined 129 patients with a BMI >35 kg/m2 attending for laparoscopic gastroplasty, comparing them with a non-obese control group with BMI <30 kg/m2. The primary outcome measure to define ‘difficult intubation’ was an IDS>5. The incidence of IDS>5 was 2.3% in non-obese and 15% in obese patients. The modified Mallampati Score 3 or 4 was identified by multivariate analysis as an independent risk factor with sensitivity 85%, specificity 62% and PPV 29%. Calculation of the likelihood ratio (85/100−62) gives an LR of 2 which indicates that if the test is considered useful by the authors it is because of the high prevalence of difficult intubation (by their definition), not because the test is particularly ‘good’. Obese patients may have smaller FRC volumes than non-obese patients which indicates that the time for preoxygenation to a certain end-tidal oxygen value may be shorter but the store of oxygen in the FRC will be smaller. In the study quoted, the time to reach an end-tidal oxygen >85% was similar in obese and non-obese patients (mean 4, range 1–10 minutes) but the minimal oxygen saturation during intubation was significantly lower in the obese group with a value of 50% being recorded in one patient. As expected, oxygen saturations were lower during intubation in those patients who were difficult to intubate. Obesity may be associated with a higher risk of gastro-oesophageal reflux. Acromegaly Acromegaly is one of the medical conditions with an association with difficult intubation with two retrospective studies quoting a prevalence of 12 and 30%. In one prospective study30 of 128 patients with acromegaly undergoing elective trans-sphenoidal resection, the prevalence of a Grade 3 laryngeal view was reported as 26%. However, this is incorrect because the appropriate method of Cormack and Lehane laryngeal view grading is the optimal view including external laryngeal manipulation. When ELM was applied the prevalence of Grade 3 view was only 10% and these patients required more than two attempts at direct laryngoscopy, a change of blade or the use of the gum-elastic bougie. Facemask ventilation was possible in all patients and all patients were intubated successfully. Head and neck disease Tests used to predict difficult airway management in general surgical patients may not be appropriate when the presenting disease process affects the head, neck or mediastinum. The disease process itself, previous surgery or radiotherapy may mean that gross narrowing or distortion is present at laryngeal level, in the sub-glottis or trachea. The prevalence of difficult intubation and difficult ventilation are much higher than in the general population, with difficult intubation rates of 5–10% in ENT surgery and >25%, if there is a tumour of the airway. Pharyngo-laryngeal disease In a prospective study31, 181 consecutive patients with laryngeal disease scheduled to undergo laryngeal microsurgery under general anaesthesia with orotracheal intubation were included. Patients with acute respiratory insufficiency, with a baseline oxygen saturation <85%, were excluded. It can be seen that this study is one involving those patients with laryngeal disease whom the authors felt were suitable for managing under general anaesthesia. It is unfortunate that the specific criteria for making this decision are not described because the decision to manage a patient with airway obstruction by tracheostomy or intubation under local anaesthesia may be difficult. Preoperative evaluation was carried out by an experienced anaesthetist and 11 variables were measured (Table 5). In all patients, intubation was attempted by direct laryngoscopy under general anaesthesia with the patient's head in the sniffing position, and spontaneous ventilation prior to the administration of a muscle relaxant. Intubation was defined as difficult if it was not possible, the best laryngeal view was Cormack and Lehane III or IV, the disease process made identification of laryngeal structures and the glottic lumen impossible or if auxiliary equipment was needed to achieve intubation. The auxiliary equipment was the rigid stylet, intubating fibrescope or transtracheal jet ventilation. Table 5. Variables studied in pharyngo-laryngeal disease.31 Value 0 Value 1 Modified Mallampati Class 1 and 2 Class 3 and 4 Thyromental <6.5 cm <6.5 cm Mouth opening >4 cm <4 cm Jaw protrusion Class A Class B, C Dentition Normal, no teeth Mobile, protruding Maxillary deficiency None Maxillary hypoplasia Head and neck mobility >90 degrees <90 degrees Receding mandible Normal Receding Body mass index <30 >30 Laryngeal dysfunction Hoarseness Stridor, dysphagia Supraglottic pathology No Yes Difficult intubation occurred in 54 patients (30%) and in four patients proved to be impossible, leading to tracheostomy. The prevalence of difficult intubation was 60% in those patients with a neoplastic process and 22% in those with a non-neoplastic pathology. A simplified risk score was obtained following logistic regression analysis with the optimum cut-off being five points (sensitivity 94%, specificity 76%, LR 4). Thyroid surgery Difficulty with intubation may be caused by an enlarged thyroid gland producing airway narrowing or deviation. It is common to obtain either a chest X-ray or CT scan to delineate the extent of deviation or compression of the trachea and these measurements were included in preoperative data gathered prospectively in a series of 320 patients undergoing thyroid surgery.32 It is of note that ‘patients with obvious malformations of the airway were excluded from the study’. It is difficult to know what this means but it appears that no patients were in fact excluded in the 3 year study period. The data gathered preoperatively was that which might be collected for any patient—weight, height, BMI, protruding maxilla or teeth, evident macroglossia, Mallampati, thyromental distance, inter-incisor distance and head/neck movement—and factors specific to thyroid surgery (Table 6). All intubations were undertaken under general anaesthesia with muscle relaxation and the IDS was used to quantify intubation difficulty. An IDS>5 was used to define difficult intubation. Table 6. Risk factors examined in relation to goitre.32 Easy intubation (n=303) Difficult intubation (n=17) P value Cancerous goitre 13 12 <0.001 Tracheal compression 33 12 <0.001 Presence of dyspnea 30 8 <0.001 Tracheal deviation 160 14 0.04 Toxic multinodular goitre 90 2 NS Graves disease 9 1 NS Size of goitre (mean (SD)) (mm) 58 (9) 56 (11) NS Facemask ventilation was possible in all patients, there were no failed intubations and an IDS>5 was found in 17 patients (5.3%). In 10 of these patients, intubation was achieved after using external laryngeal manipulation and in the remaining 7 patients by using the Miller blade or Magill forceps. No difficulty was encountered in passage of the endotracheal tube through the compressed or narrowed part of the trachea. Multivariate analysis revealed that a cancerous goitre, tracheal compression and presence of dyspnoea were associated with difficult intubation but the study concluded that no great difficulty was found with intubation of patients presenting with thyroid disease. This is in agreement with an older study33 from 1989 which described relatively uncomplicated intubation of 120 patients with airway compression secondary to goitres including 30 patients with acute airway distress. The presence of a large thyroid mass may alter airway management plans because emergency cricothyrotomy may not be possible if ventilation fails. There are certainly case reports34 and 35 indicating very difficult airway management with thyroid masses including one patient36 in whom awake fibreoptic intubation was planned but deteriorated immediately upon application of topical anaesthesia. Tongue abnormalities The predictive tests of difficult direct laryngoscopy which evaluate the likely line-of-sight to the larynx assume that the compliance and mobility of the tongue will be normal and that there will be no abnormal tissue in the way. Successful direct laryngoscopy requires the tongue to be retracted from the line-of-sight. If the tongue is abnormally large, bulky or poorly compliant then direct laryngoscopy may be difficult. Recently, a report37 of 5 patients indicates that impaired tongue mobility is a sensitive sign of difficulty which may be ignored initially by the anaesthetist. In all cases intubation by direct laryngoscopy failed and either fibreoptic intubation or retrograde intubation was required. The compliance of the sub-mental region may be determined subjectively by digital pressure. If it is full, woody or unyielding it indicates that tongue distraction will be difficult. Lingual tonsillar tissue Lingual tonsillar tissue is a well-recognised, but rare abnormality that may cause difficulty with intubation and ventilation and has been implicated as the cause of an airway related death. Ovassapian et al38 studied 33 patients over a 11-year period who were found to be impossible to intubate by direct laryngoscopy or had a history of unexpected failed intubation. At subsequent endoscopy, all patients were found to have lingual tonsil hyperplasia. In the 27 failed intubation patients, the laryngeal view was Grade 4 and facemask ventilation was difficult or impossible in 35%. Both patients with severely difficult or impossible facemask ventilation could be ventilated with a laryngeal mask. All patients were managed successfully by fibreoptic intubation. Lingual tonsil hyperplasia in adults is often asymptomatic but may be associated with recurrent sore throat, dysphagia, snoring or obstructive sleep apnoea. Two-thirds of patients have undergone tonsillectomy or adenoidectomy. It is not possible to see the tissue by direct inspection of the oropharynx and mirror or flexible endoscopy are needed. Lingual thyroid tissue, thyroglossal cysts and vallecular cysts are other causes of unexpected difficult intubation and ventilation. Cervical spine disease Calder39 was able to study 253 patients before cervical spine surgery in a specialist unit. A large number of the patients had rheumatoid arthritis and the prevalence of difficult intubation (Cormack and Lehane III or IV laryngeal view) was 20%, with a Grade IV prevalence of 6%. A fairly standard set of preoperative tests were performed in addition to lateral cervical radiographs. A number of patients underwent flexible fibreoptic intubation and the laryngeal view was obtained by direct laryngoscopy following fibreoptic intubation. It is not surprising that, with this very high incidence of difficult intubation, that the predictive tests performed better than in general surgical patient. Cervical osteophytes40 may give rise to difficult direct laryngoscopy and difficult fibreoptic intubation and the cervical spine abnormalities in Down syndrome41 may influence airway management. Methods, scores and indices Whilst individual tests may be poorly predictive in general surgical patients, a combination of tests may increase the predictive power. The specificity increases but there will be some loss of sensitivity. Frerk42 demonstrated in a small study that the combination of the Mallampati and thyromental distance was more predictive than either test alone. A recent West African study43 in 380 consecutive patients showed that the combination of a modified Mallampati 3 or 4, inter-incisor distance of or less than 4 cm and thyromental distance of or less than 6.5 had a sensitivity 85% and specificity of 95% giving an LR of 17 in predicting difficult direct laryngoscopy. A number of tests may be used to build a risk index or score. A few will be described in more detail. Wilson risk-sum score Five factors, three objective and two subjective, contribute to the final score44 (Table 7). It does not appear to be commonly performed now, but the idea behind it is valuable. It suggests that a range of factors is important and calculation of the score forces the anaesthetist to at least consider the five factors. In one early study45, the PPV was only 9% but in a recent study46 in 372 obstetric patients undergoing caesarean section the LR of a score equal to or more than 2 was >20. Table 7. Wilson risk sum.49 Score Weight <90 kg 0 90–110 kg 1 >110 kg 2 Head and neck movement >90 degrees 0 90 degrees 1 <90 degrees 2 Jaw movement, jaw protrusion Incisor gap >5 cm, Class A 0 Incisor gap <5 cm, Class B 1 Incisor gap <5 cm, Class C 2 Receding mandible Normal 0 Moderate 1 Severe 2 Buck teeth Normal 0 Moderate 1 Severe 2 LEMON The LEMON method was devised by the US National Emergency Airway Management course for use in a resuscitation room setting. LEMON is an acronym for Look-Evaluate-Mallampati-Obstruction-Neck and the feasibility of using the method was evaluated in 100 patients47 presenting to a resuscitation room. It was possible in all patients to evaluate the Look, Obstruction and Neck components but particular difficulty was encountered with data requiring mouth opening to command. The Mallampati score was unavailable in 43% patients and inter-incisor distance in 10%. The authors note that there is an inverse relationship between the likelihood of voluntary mouth opening and need for intubation. Some of the value of the LEMON method is that it does ensure a formal airway assessment in all patients. There is currently no LEMON score. El-Ganzouri risk index A prospective study48 of 10 507 consecutive patients determined the relationship of seven preoperative airway variables to intubation difficulty and allowed development of a simplified risk index. It is unfortunate that the study protocol excluded ‘patients with obvious malformations of the airway who were scheduled for awake intubation’. There is no information on what constituted obvious malformations nor how many patients were intubated awake in the study period. The seven variables were mouth opening (<4 or >4 cm), thyromental distance (<6.0, 6.0–6.5 or >6.5 cm), Mallampati (I–III), neck movement (<80,80–90 or >90°), jaw protrusion (Yes/No), body weight <90, 90–110 or >110 kg) and history of difficult intubation (None, questionable or definite) with each component scoring 0, 1, or 2. Cormack and Lehane Grades 3 and 4 views were used to define difficulty and the prevalence of these were 5 and 1%, respectively. As the airway risk score increased the sensitivity fell, but specificity increased, without a clear cut-off point. Many difficult intubations had a low risk index score but few normal patients had a score over 4. Arnè risk index A French study49 devised a risk index from 1200 consecutive ENT and general surgical patients defining difficult intubation as requiring an alternative intubation technique to standard direct laryngoscopy. The techniques used included the gum elastic bougie, fibreoptic intubation, the Bullard laryngoscope and PCV laryngoscope. The risk index (Table 8) with a threshold score of 11 was prospectively studied in another 1090 patients and the results given separately for general surgical patients (sensitivity 94%, specificity 96%), non-cancer ENT patients (sensitivity 90%, specificity 93%) and cancer ENT patients (sensitivity 92%, specificity 66%). Table 8. Arné Risk Index, simplified score.24 Factor Scoring Points History of DI Yes 10 Pathologies associated with DI Yes 5 Clinical symptoms Yes 3 Thyromental distance <6.5 cm 4 Head/neck movement 80–100 2 <80 5 Mallampati Class 2 2 Class 3 6 Class 4 8 Mouth opening, jaw protrusion 3.5–5.0 cm, B 3 <3.5 cm, C 13 Clinical practice Anaesthetists should always undertake an airway evaluation and choose the appropriate airway strategy. The initial evaluation screens for expected difficulty and will comprise a history and examination. The examination takes little time and should be conducted in an orderly sequence4 noting whether the patient looks normal, the presence of awkward or loose teeth, mouth opening, jaw protrusion, inspection of the oropharynx, position and availability of the larynx, length and thickness of the neck and the range of motion of the head/neck. In general surgical patients, the tests are poor at predicting difficult airway management and the point at which the anaesthetist determines that a preoperative abnormality will influence airway management is a professional judgement which may later prove to be correct or incorrect. The more numerous or serious the abnormalities detected preoperatively, the more likely is the strategy to change and to involve instrumentation of the airway in the awake patient. If the disease process impinges on the airway, the full extent of the narrowing or distortion should be evaluated by imaging or flexible nasendoscopy. Further evaluation determines whether intubation should be through the nose or mouth, whether local anaesthetic blocks are possible, whether the patient is suitable for an awake intubation and the back-up strategy should the initial awake intubation attempt fail. The repertoire of airway strategies for a general anaesthetist should cover management of unanticipated difficult intubation or ventilation, anticipated difficult direct laryngoscopy, the patient who requires awake intubation, the patient with a full-stomach and the patient with upper airway obstruction. The most commonly employed airway strategy is the default strategy—that which is adopted when no significant problems are anticipated. The default strategy for intubation includes general anaesthesia, muscle relaxation (or abolition of laryngeal reflexes by other means) and intubation by optimal direct laryngoscopy. It also includes a back-up method of intubation. When a practitioner is confident of the back-up plan for failed direct laryngoscopy, weak predictors of difficult direct laryngoscopy such as the Mallampati or the thyromental distance become less important in elective anaesthesia. Direct laryngoscopy can be attempted carefully and if it is difficult, abandoned early in favour of the back-up plan. Preparation for difficulty The original1 and updated4 ASA guidelines include ‘Preparation’ as a specific component of difficult airway management. Difficult airway trolley At least one portable storage unit that contains specialised equipment should be available within the theatre complex. This complements the airway equipment available in each operating room. There is no definitive list of equipment which should be available and the content of the trolley should be decided by the local anaesthetists according to the likely caseload. For a general hospital with an open accident and emergency unit it is common for the trolley to be organised into drawers containing alternative laryngoscope blades, tracheal tubes of assorted sizes, introducers, stylets and tube-exchange catheters, laryngeal masks including the intubating laryngeal mask with its specialised tubes, a range of oral and fibreoptic intubation airways such as the Berman, a retrograde intubation kit, transtracheal jet ventilation needles, a Sanders injector, and equipment for awake intubation. An intubating fibrescope and light source may be either within the difficult airway trolley or additional to it but should be immediately available. There should be secure arrangements for checking the contents daily and re-stocking. Assistance An assistant should be available when difficult airway management is anticipated. An additional anaesthetist is useful when great difficulty is expected. Oxygenation Supplementary oxygen should be administered throughout the period of airway instrumentation and it is easy to forget this during awake intubation. Patient An explanation of the problems and possible solutions should be given to the patient in the process of consent. If airway management is expected to be difficult the options are to postpone or abandon surgery, undertake it under local anaesthesia infiltration or peripheral nerve block, gain senior help or use an airway technique not expected to be difficult including awake intubation. Anxiolysis may be provided by good rapport with the patient or with sedation such as an oral benzodiazepine. A sedative premedication should be avoided if there is airway compromise. Antisialogogue premedicant is particularly useful when an awake intubation or fibrescopic technique is to be used. Local anaesthesia works more quickly and provides more dense analgesia when the mucosa is dry. Generally an antisialogogue such as atropine 0.6 mg IM or glycopyrronium 0.6 mg IM should be given preoperatively or glycopyrronium 0.2–0.4 mg intravenously at the start of anaesthetic care. Prevention of gastro-oesophageal reflux50 will reduce the incidence of aspiration. In the elective patient a period of 6 hours without food and 4 hours without liquid is adequate, and in children the liquid free period should be only 2 hours. In other situations, where the stomach may be full, or lower oesophageal barrier pressure is reduced, further actions include nasogastric drainage, a prokinetic agent such as metoclopramide 10–20 mg intravenously, a non-particulate antacid such as 30 ml 0.3 M sodium citrate, or inhibition of gastric acid production by ranitidine 150–300 mg orally or 50 mg slowly intravenously or by a proton pump inhibitor such as omeprazole 30 mg orally. Pharmacological inhibition of gastric acid production is most successful if medication is given the night before surgery and on the morning of surgery. Practice points • airway evaluation is essential in all patients • evaluation determines the airway strategy • the airway strategy will be influenced by the level of airway maintenance and protection required, the likely difficulty with airway management and the risk of aspiration • strong predictors of difficulty are a previous history, signs or symptoms of airway compromise, airway pathology, limited mouth opening or neck mobility and obvious abnormality of the jaw, tongue or face • the low prevalence of difficult intubation makes prediction difficult • airway strategy must cope with unanticipated difficult ventilation and intubation • anaesthetists should have a number of pre-formulated strategies for the commonest problems Research agenda • an end to small, unscientific prediction studies • good quality studies in specialised areas with a high prevalence of difficult airway management to devise risk indices appropriate to that sub-specialty • independent validation of published scoring systems • evaluation of the usefulness in economic, time-management or patient morbidity terms of published predictive tests or scores • studies of the linkage between evaluation and strategy References 1 R.A. 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Borron et al., A survey of tracheal intubation difficulty in the operating room: a prospective observational study, Acta Anaesthesiologica Scandinavica 45 (2001), pp. 327–332. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 16 J.L. Benumof, Intubation difficulty scale: anticipated best use, Anesthesiology 87 (1997), pp. 1273–1274. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 17 W.H. Rosenblatt, Preoperative planning of airway management in critical care patients, Critical Care Medicine 32 (2004), pp. S186–S192. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 18 M. Janssens and G. Hartstein, Management of difficult intubation, European Journal of Anaesthesiology 18 (2001), pp. 3–12. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 19 S.M. Yentis, Predicting difficult intubation—worthwhile exercise or pointless ritual, Anaesthesia 57 (2002), pp. 105–109. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 20 I. Calder, J. Picard and M. Chapman et al., Mouth opening: a new angle, Anesthesiology 99 (2003), pp. 799–801. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 21 J.A. Williamson, R.K. Webb and S. Szekely et al., Difficult intubation: an analysis of incident reports, Anaesthesia and Intensive Care 21 (2000), pp. 602–607. 22 Z.H. Khan, A. Kashfi and E. Ebrahimkhani, A comparison of the upper lip bite test (a simple new technique) with modified mallampati classification in predicting difficulty in endotracheal intubation: a prospective blind study, Anesthesia and Analgesia 96 (2003), pp. 595–599. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Full Text via CrossRef 23 M. Lewis, S. Keramati, J.L. Benumof and C.C. Berry, What is the best way to determine oropharyngeal classification and mandibular space length to predict difficult laryngoscopy?, Anesthesiology 81 (1994), pp. 69–75. Abstract-MEDLINE | Abstract-EMBASE 24 S.R. Mallampati, S.P. Gatt and L.D. Gugino et al., A clinical sign to predict difficult intubation: a prospective study, Canadian Journal of Anaesthesia 32 (1985), pp. 429–434. Abstract-EMBASE | Abstract-MEDLINE 25 G.T. Samsoon and J.B. Young, Difficult tracheal intubation: a retrospective study, Anaesthesia 42 (1987), pp. 487–490. Abstract-EMBASE | Abstract-MEDLINE 26 D. Cattano, E. Panicucci and A. Paolicchi et al., Risk factors assessment of the difficult airway: an Italian survey of 1956 patients, Anesthesia and Analgesia 99 (2004), pp. 1774–1779. Abstract-Elsevier BIOBASE | Abstract-EMBASE | Full Text via CrossRef 27 S.A.L. Ramadhani, L.A. Mohamed, D.A. Rocke and E. Gouws, Sternomental distance as the sole predictor of difficult laryngoscopy in obstetric anaesthesia, British Journal of Anaesthesia 77 (1996), pp. 312–316. 28 A.D. Farmery, Sternomental distance as a predictor of difficult laryngoscopy, British Journal of Anaesthesia 78 (1997), p. 626. Abstract-EMBASE | Abstract-MEDLINE 29 P. Juvin, E. Lavaut and H. Dupont et al., Difficult tracheal intubation is more common in obese than in lean patients, Anesthesia and Analgesia 97 (2003), pp. 595–600. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Full Text via CrossRef 30 H. Schmitt, M. Buchfelder, M. Radespiel-Troger and R. Fahlbusch, Difficult intubation in acromegalic patients; incidence and predictability, Anesthesiology 93 (2000), pp. 110–114. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 31 M.A. Ayuso, X. Sala, M. Luis and J.M. Carbo, Predicting difficult orotracheal intubation in pharyngo-laryngeal disease: preliminary results of a composite index, Canadian Journal of Anaesthesia 50 (2003), pp. 81–85. Abstract-EMBASE | Abstract-MEDLINE 32 A. Bouaggad, S.E. Nejmi, M.A. Bouderka and O. Abbassi, Prediction of difficult tracheal intubation in thyroid surgery, Anesthesia and Analgesia 99 (2004), pp. 603–606. Abstract-Elsevier BIOBASE | Abstract-EMBASE | Full Text via CrossRef 33 A.R. Saha, C. Burnett, A. Alfonso and B.M. Jaffe, Goiters and airway problems, American Journal of Surgery 158 (1989), pp. 378–380. 34 G.S. Voyagis and P.K. Kyriakos, The effect of goiter on endotracheal intubation, Anesthesia and Analgesia 84 (1997), pp. 611–612. Abstract-MEDLINE | Full Text via CrossRef 35 H.G. Wakeling, A. Ody and A. Ball, Large goitre causing difficult intubation and failure to intubate using the intubating laryngeal mask airway: lessons for next time, British Journal of Anaesthesia 81 (1998), pp. 979–981. Abstract-MEDLINE | Abstract-EMBASE 36 I.C. Shaw, E.A. Welchew, B.J. Harrison and S. Michael, Complete airway obstruction during awake fibreoptic intubation, Anaesthesia 52 (1997), pp. 582–585. Abstract-MEDLINE | Abstract-EMBASE 37 C. Rosenstock and M.S. Kristensen, Decreased tongue mobility—an explanation for difficult endotracheal intubation, Acta Anaesthesiologica Scandinavica 49 (2005), pp. 92–94. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 38 A. Ovassapian, R. Glassenberg and G.I. Randel et al., The unexpected difficult airway and lingual tonsil hyperplasia, Anesthesiology 97 (2002), pp. 124–132. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 39 I. Calder, J. Calder and H.A. Crockard, Difficult direct laryngoscopy in patients with cervical spine disease, Anaesthesia 50 (1995), pp. 756–763. Abstract-MEDLINE | Abstract-EMBASE 40 D.N. Ranasinghe and I. Calder, Large cervical osteophyte—another cause of difficult flexible fibreoptic intubation, Anaesthesia 49 (1994), pp. 512–514. Abstract-MEDLINE | Abstract-EMBASE 41 T. Hata and M.M. Todd, Cervical spine considerations when anaesthetizing patients with down syndrome, Anesthesiology 102 (2005), pp. 680–685. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef 42 C.M. Frerk, Predicting difficult intubation, Anaesthesia 46 (1991), pp. 1005–1008. Abstract-EMBASE | Abstract-MEDLINE 43 N.A. Merah, D.T. Wong and D.J. Ffoulkes-Crabbe et al., Modified mallampati test, thyromental distance and inter-incisor gap are the best predictors of difficult direct laryngoscopy in West Africans, Canadian Journal of Anaesthesia 52 (2005), pp. 292–296. 44 M.E. Wilson, D. Spiegelhalter, J.A. Robertson and P. Lesser, Predicting difficult intubation, British Journal of Anaesthesia 61 (1988), pp. 211–221. 45 J.D.L. Oates, A.D. Macleod and P.D. Oates et al., Comparison of two methods for predicting difficult intubation, British Journal of Anaesthesia 66 (1991), pp. 305–309. Abstract-EMBASE | Abstract-MEDLINE 46 S. Gupta, S. Pareek and S.C. Dulara, Comparison of two methods for predicting difficult intubation in obstetric patients, Middle East Journal of Anesthesiology 17 (2003), pp. 275–285. Abstract-MEDLINE 47 M.J. Reed, L.M. Rennie and M.J.G. Dunn et al., Is the LEMON method an easily applied emergency airway assessment tool?, European Journal of Emergency Medicine 11 (2004), pp. 154–157. Abstract-MEDLINE | Full Text via CrossRef 48 A.R. El-Ganzouri, R.J. McCarthy and K.J. Tuman et al., Preoperative airway assessment: predictive value of a multivariate risk index, Anesthesia and Analgesia 82 (1996), pp. 1197–1204. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef 49 J. Arné, P. Descoins and J. Fusciardi et al., Preoperative assessment for difficult intubation in general and ENT surgery: predictive value of a clinical multivariate risk index, British Journal of Anaesthesia 80 (1998), pp. 140–146. Abstract-EMBASE | Abstract-MEDLINE 50 A. Ng and G. Smith, Gastroesophageal reflux and aspiration of gastric contents in anesthetic practice, Anesthesia and Analgesia 93 (2001), pp. 494–513. Abstract-EMBASE | Abstract-Elsevier BIOBASE | Abstract-MEDLINE | Full Text via CrossRef

"FL_Medic, and Everyone," In addition to the material already posted above. Here is a great article which covers the assessment of analgesia under anesthesia. The majority of the study discusses 'perioperative' conditions, yet i am sure that we all know this info can be extarpolated to both the CCT-flight environment S/P RSI in the setting of contuing paralysis and sedation as well as initally. Hope This Helps, ACE844 [/font:e8cbdcc9fb] [quote=Best Practice & Research Clinical Anaesthesiology Volume 20, Issue 1 , March 2006, Pages 161-180 Monitoring Consciousness doi:10.1016/j.bpa.2005.09.002 Copyright © 2005 Elsevier Ltd All rights reserved. 14 Monitoring analgesia Bruno Guignard MD, Département d'Anesthésie Réanimation, Hôpital Ambroise Paré, 9 avenue du général de Gaulle, 92100 Boulogne Billancourt, France Available online 17 March 2006.] Analgesia (pain relief) amnesia (loss of memory) and immobilisation are the three major components of anaesthesia. The perception of pain, and therefore, the need for analgesia, is individual, and the monitoring of analgesia is indirect and, in essence, of the moment. Under general anaesthesia, analgesia is continually influenced by external stimuli and the administration of analgesic drugs, and cannot be really separated from anaesthesia: the interaction between analgesia and anaesthesia is inescapable. Autonomic reactions, such as tachycardia, hypertension, sweating and lacrimation, although non-specific, are always regarded as signs of nociception or inadequate analgesia. Autonomic monitoring techniques, such as the analysis of heart rate variability, laser Doppler flowmetry, phlethysmographically derived indices and the pupillary light reflex, may help to quantitate reactions of the autonomic nervous system. For the past few years, automated electroencephalographic analysis has been of great interest in monitoring anaesthesia and could be useful in adapting the peroperative administration of opioids. A range of information collected from the electroencephalogram, haemodynamic readings and pulse plethysmography might be necessary for monitoring the level of nociception during anaesthesia. Information theory, multimodal monitoring, and signal processing and integration are the basis of future monitoring. Monitoring analgesia Definitions Anaesthesia is a state of unconsciousness induced by a drug. The three components of anaesthesia are analgesia (pain relief), amnesia (loss of memory) and immobilisation, even though some authors have tried to reduced anaesthesia to a lack of perception or recall of noxious stimulation.1 The drugs used to achieve anaesthesia usually have varying effects in each of these areas. Some drugs may be used individually to achieve all three targets, whereas others have only analgesic or sedative properties and may be used individually for these purposes or in combination with other drugs to achieve full anaesthesia. Physiological methods of monitoring must be used to assess anaesthetic depth as normal reflex methods will not be reliable. The major problem is to define what anaesthesia and analgesia really are. In this regard combinations of anaesthetics and analgesics, known as ‘balanced anaesthesia’, do not help to provide a practical understanding of the concept of depth of anaesthesia paradigm.2 Pain is one of the most unpleasant sensations in existence, and even in fetal life noxious stimulation causes detectable stress responses. The prevention and treatment of pain are a basic human right, so a better comprehension of the detailed action of analgesics on pain relief is a challenge for the future.3 There have been many reports on pain research from various fields of medical science, for example physiology, pharmacology, biochemistry and immunology, and the knowledge acquired of the mechanisms of pain perception in the human brain can be directly related to the treatment of pain and the monitoring of pain relief. Pain is a more complicated sensation than other somatosensory modalities such as touch and vibration, as the degree of feeling can be easily changed by a change in mental state, pain being, by its very nature, subjective. In conscious subjects, pain is greatly affected by the amount of attention paid to and distraction from a noxious stimulus, but this is not the case under sedation or general anaesthesia. Human, as well as animal, studies on pain perception are necessary, but only a relatively small number of the former have been carried out because such studies must be non-invasive. Recently, non-invasive techniques have been developed, such as electroencephalography (EEG), magnetoencephalography, positron emission tomography, functional magnetic resonance imaging and transcranial magnetic stimulation, and the number of reports on pain perception using these techniques has progressively increased over the past 10 years.4, 5, 6 and 7 Analgesia is defined by the relief of pain, in other words by absence of pain in response to stimulation that would normally be painful. This definition is subjective because pain is defined by the International Association for Study of Pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. Pain is a subjective sensation because of this individuality and is also difficult to assess because of the inability to communicate directly about the sensation of pain. Instead, indirect clinical signs of pain are used during anaesthesia. Because of the difficulty in determining when pain is present during general anaesthesia, it is assumed that something that is painful involves reactions of the body that are visible by clinical observation or by monitoring. Analgesia could also be defined by the combination of a stable state and the absence of pain—if the subject were conscious—during and immediately after a painful stimulus. One of the great paradoxes of analgesia is that, by its very nature, it cannot be predicted because of the perpetual interaction between variations in stimulation and variations in the patient's anaesthetized state. Like anaesthesia, analgesia is a continuum between a perceived absence of pain and maximum pain. Analgesia can be partial and incomplete, and the notion of a threshold of analgesia depends on the state of the patient and is continually under influence of external stimuli. Which parameters should be used to monitor analgesia? Individual perception of pain This chapter does not aim to consider the auto-evaluation of pain: a discussion of quantitative sensory testing of the nociceptive system in conscious subjects can be found in an article by Dotson.8 Instead, we will look at methods that could be used in unconscious patients; elucidating the mechanisms underlying pain perception in unconscious subjects could help us to understand analgesia. There is a relationship between the pain system and the motor, sensory and autonomic systems. Alterations to these systems, for example in a child with a significant neurological impairment, can have a profound and unique impact on the pain experience and analgesia.9 Likewise, hypoalgesia in borderline personality disorders may primarily be due to altered intracortical processing similar to that seen in certain meditative states: there is no general impairment of the sensory-discriminative component of pain, no hyperactive descending inhibition, and no attention deficits revealed by laser evoked potentials.10 There are also gender differences in pain perception11, 12 and 13, which might be of clinical relevance in morphine titration.14 These differences could be explained by a more pronounced descending inhibitory control.15 Nevertheless, there is no difference in desflurane minimum alveolar concentration (MAC) between young men and women.16 Clinical variation in the perception of analgesia Both the Ramsay Sedation Score and the Observer's Assessment of Alertness/Sedation Scale include response to pain in their graduated scales, reflecting an abolition of conscious pain perception.17 and 18 The Cardiac Analgesic Assessment Scale is a postoperative pain evaluation instrument used in children after cardiac surgery, providing more information than a visual analogue scale completed by an observer.19 Studies performed with anaesthetic personnel show that no variable was considered entirely specific for either intraoperative pain or depth of anaesthesia. Changes in breathing rate and volume, blood pressure, heart rate and lacrimation, as well as the presence of moist and sticky skin, were given higher scoring values as indicators of pain than as indicators of depth of anaesthesia.20 Movement and minimum anaesthetic concentration Under general anaesthesia, movement in response to painful stimulation is the end-point classically used to assess the potency of anaesthetic agents. Withdrawal reflexes are tailored to produce the most appropriate movement according the site at which the noxious stimulus is applied, as flexors or extensors could act as the primary movers. Areas from which a reflex can be sensitised closely match those from which the reflex itself can be evoked, providing the spinal cord is intact.21 The principal site of response to nociceptive stimulation is spinal22, and the interaction between analgesia and anaesthesia is inescapable. Interconnection between haemodynamics and nociception Somatosympathetic reflexes have been characterised for more than 30 years23, but the exact interaction between systems is still being researched because relationships are complexes.24 and 25 Some neurones from the rostral ventrolateral medulla have spinally projecting axons, and their responses to noxious mechanical, thermal and/or electrical stimulation have been shown to be accompanied by increases in arterial pressure in anaesthetised rats. In humans with spinal cord transection above vertebral level T5, profound elevations in systolic blood pressure and pulse pressure were induced by bladder distension: the authors noticed a decrease in heart rate in three of seven patients.26 A baroreflex mechanism may explain hypertensive hypoalgesia. At rest, arterial baroreceptors are stimulated during the systolic upstroke of the pressure pulse wave. Stimulation of the baroreceptors by natural increases in blood pressure during the systolic phase of the cardiac cycle was associated with dampened nociception. There are also interactions between angiotensin and pain perception. Untreated hypertensive subjects showed a reduced perception to painful stimuli when compared with normotensive individuals. A significant reduction in both pain threshold and tolerance was observed during enalapril or losartan treatment.27 Hypertension diminishes pain perception, and the electrical stimulation of vagal afferent nerves (cardiopulmonary baroreceptors) suppresses nociceptive responses. In addition, both a pharmacological elevation of blood pressure and vascular volume expansion produce anti-nociception.28 Autonomic reactions Autonomic reactions, such as tachycardia, hypertension, sweating and lacrimation, have usually been regarded as signs of nociception or inadequate analgesia, heart rate being less consistent than blood pressure response. Isoflurane used as a sole agent is unable to suppress haemodynamic reactions (blood pressure and heart rate) to painful stimuli. The lack of motor response is not an accurate predictor of the ability of an agent to depress haemodynamic reactions29, but haemodynamic responses after noxious stimulation such as laryngoscopy or tracheal intubation are still considered to be the responses which are easiest to interpret during anaesthesia.30 Motor or haemodynamic responses to nociceptive stimuli could, a posteriori, serve to adapt the dosage of hypnotic or analgesic agents, and heart rate variations have been used to automatically amend remifentanil target-controlled infusion during general anaesthesia.31 Tentative measures for standardisation have been proposed by Evans, using the PRST (blood Pressure, heart Rate, Sweating, Tears) score of responsiveness (Table 1). Table 1. Evans' PRST score. Clinical signs Conditions Score Systolic arterial pressure (mmHg) <Control+15 0 <Control+30 1 >Control+30 2 Heart rate (beats per minute) <Control+15 0 <Control+30 1 >Control+30 2 Sweating None 0 Skin moist to touch 1 Visible beads of sweat 2 Tears No excess of tears in open eye 0 Excess of tears in open eye 1 Tears overflow closed eye 2 Stimulation of the sympathetic system in response to noxious stimulus is, however, not always the case. Parasympathetic stimulation can occur, with opposite responses (Table 2). Table 2. Responses of major organs to autonomic nerve impulses. Organ Sympathetic stimulation Parasympathetic stimulation Heart Increased heart rate β1 (and β2) Decreased heart rate Increased force of contraction β1 (and β2) Decreased force of contraction Increased conduction velocity Decreased conduction velocity Arteries Constriction (α1) Dilatation Dilatation (β2) Veins Constriction (α1) Dilatation (β2) Lungs Bronchial muscle relaxation (β2) Bronchial muscle contraction Increased bronchial gland secretions Eye Dilatation of pupil (α) Constriction of pupil Contraction of sphincters (α) Increased lacrimal gland secretions Liver Glycogenolysis (β2 and α) Glycogen synthesis Gluconeogenesis (β2 and α) Lipolysis (β2 and α) Kidney Renin secretion (β2) Bladder Detrusor relaxation (β2) Detrusor contraction Contraction of sphincter (α) Relaxation of sphincter Uterus Contraction of pregnant uterus (α) Relaxation of pregnant and non-pregnant uterus (β2) Submandibular and parotid glands Viscous salivary secretions (α) Watery salivary secretions Different types of pain can lead to particular reactions. For example, the mesenteric Pacinian corpuscle is the baroreceptor that probably initiates the vasomotor reflexes in skin and muscle32 during abdominal pain. Chronotropic and inotropic responses to the noxious stimulation caused by laryngoscopy or surgical stimulation can be effectively suppressed by beta-receptor blockade33, and esmolol leads to analgesia and a reduction in cardiovascular responses to pain in the non-sedated rat.34 Esmolol does not attenuate the heart rate response to sternotomy but does attenuate the increase in blood pressure in patients receiving chronic beta-blocker therapy.35 Perioperative esmolol administration during anaesthesia reduced the intraoperative use of isoflurane and fentanyl by 25%, decreased haemodynamic responses and reduced morphine consumption by 30% for the first 3 postoperative days in patients undergoing a hysterectomy.36 Vagal afferent nerves are thought to mediate autonomic responses evoked by noxious mechanical or chemical oesophageal stimuli, and participate in the perception of pain originating from the oesophagus. The fibres involved in this mechanism include both A and C fibres.37 Sesay et al have evaluated electrocardiographic (ECG) spectral analysis during surgery on the cerebellopontine angle. Vagal reactions were defined as a decrease in heart rate or an increase in HF of more than 10% of the pre-stimulus value. This monitoring permits the detection of intraoperative vagal reactions earlier than is allowed by the conventional monitoring of heart rate38, as could be seen during a study of hysteroscopy.39 The vagus nerves supply the guinea-pig oesophagus with nociceptors in addition to tension mechanoreceptors.37 Susceptibility to vasovagal reactions after a noxious stimulus may be associated with individual differences in baroreflex sensitivity.40 Monitoring the cardiac autonomic system: heart rate variability Cardiac autonomic function is estimated by heart rate variability measures and is expressed in the time domain as the mean of R–R intervals for normal heart beats and the standard deviation of all normal R–R intervals. The spectral analysis of heart rate variability allows a continuous, non-invasive quantification of cardiac autonomic function, pure vagal activity being assessed by high-frequency power (0.15–0.4 Hz). Low-frequency power (0.04–0.15 Hz) reflects both parasympathetic and sympathetic control. Numerous studies of ischaemic heart disease have used this method, demonstrating the clinical significance of heart rate variability analysis. An acute noxious stimulus appears to produce an increase in respiratory-related sympathetic heart rate control and a significant decrease in respiratory-related parasympathetic control in adults and infants. Stressful events during the heel-prick procedure in newborn infants41 or painful stimuli in children42 could be evaluated by this method. With increasing age, the sympathetic and parasympathetic changes appear to be less intense but more sustained.43 Limitations of this method are artefact detection and the necessity for a long enough period of signal sampling. Wavelet analysis could be helpful with this indication.44 Skin vasomotor reflexes Testing the skin vasomotor reflexes (SVmR) by laser Doppler flowmetry is a recognised method of measuring peripheral dysautonomia and can detect an impairment of the reflex control of fingertip blood flow in both diabetes mellitus and leprosy.45 The reflex control of fingertip blood flow is assessed by measuring the reduction in laser Doppler flowmetry induced by a deep inspiratory gasp, a cold challenge of immersing the contralateral hand in cold water or electrostimulation of the ulnar nerve. Patients with diabetic neuropathy had resting laser Doppler flowmetry levels significantly lower than those of the uncomplicated group and showed a substantial impairment of both the inspiratory gasp and cold challenge reflexes.46 A sympathetic vasoconstrictor reflex is induced by noxious stimulation: laryngoscopy alone and intubation with laryngoscopy significantly reduced skin blood flow.47 Shimoda et al evaluated SVmR in response to laryngoscopy. A decrease in SVmR amplitude to less than 0.1 u before laryngoscopy is associated with blood pressure stability. SVmR amplitude and systolic blood pressure changes showed a significant linear correlation.48 SVmR is also useful to estimate objectively the level of somatosensory block induced by regional anaesthesia.49 and 50 Shimoda et al demonstrated that the level of current that induced the SVmR was proportional to the depth of anaesthesia induced by sevoflurane, and that the duration of electrostimulation (i.e. painful increase) was correlated to the magnitude of the SVmR.51 Thus, the SVmR could be helpful in the objective assessment of nociception and anti-nociceptive effects in individual cases. These authors also investigated the SVmR and haemodynamic responses to the insertion of an intubating laryngeal mask airway and found that the most stressful period was removal of the airway.52 Nakahara et al determined the MAC of anaesthetic that blocked the SVmR to surgical incision (MACBVR) for sevoflurane in 37 patients.53 They found that the MACBVR contribution to the total anaesthetic MAC multiple was 1.75 MAC for sevoflurane alone and 1.43 MAC when 50% nitrous oxide was used. There was no relationship between the amplitude of the reduction in skin blood flow and any changes in haemodynamic variables. Owing to its resistance to chronic ischaemia, the SVmR is preserved in chronically ischaemic limbs with non-diabetic, atherosclerotic peripheral arterial disease.54 Neuropeptide Y participates in sympathetically mediated cutaneous vasoconstriction.55 Owing, however, to the cost of the device to measure its level, this technique is used only in research. Plethysmography Plethysmogram amplitude Sustained pinching of the interdigital webs of the hands of human volunteers induced a tonic reflex vasoconstriction in the stimulated hand with a rather slow adaptation rate and no signs of habituation between trials. Step increases in the pinching force in the course of a stimulus were reflected by a decrease in amplitude of the plethysmogram.56 This reflex occurred at a spinal level but could be inhibited by the cerebral hemispheres.57 Skin incision is followed by a clear sympathetic vasoconstrictor response in the plethysmographic signal, and suppression of the photoplethysmographic pulse wave reflex to a nociceptive stimulus has also been found to predict a reduced haemodynamic response to tracheal intubation.58 The pulse wave reflex may be a better predictor than other variables. In another study, the best variables for logistic regression classification in movers versus non-movers at incision appeared to be response entropy, instant RR and plethysmogram notch amplitude. Plethysmogram notch amplitude was measured as the distance from the baseline to the lowest value of the notch (Figure 1).59 Nevertheless, arterial pressure was not incorporated into the variables studied. (20K) Figure 1. Parameters measured from the pulse plethysmography waveform. Pulse transit time PTT was originally measured by recording the time interval between the passage of the arterial pulse wave at two consecutive sites. More recently, for ease of measurement, the electrocardiographic R or Q wave has been used as the starting point as it approximately corresponds to the opening of the aortic valve. This ‘new’ pulse transit time (rPTT), the interval between ventricular electrical activity and the arrival of a peripheral pulse waveform, has been used to detect changes in autonomic tone and in inspiratory effort. Noxious stimulation can affect this parameter: during anaesthesia, rPTT decreased by an average of 43±25 ms in response to endotracheal intubation but did not vary in response to the insertion of laryngeal mask airway or to a surgical stimulus.60 This measure does not seem suitable, but further studies are needed. The major problem with SVmR and plethysmography-derived measures is that skin blood flow is profoundly influenced by not only pathological states, but also thermoregulatory state, age and emotional stress.61, 62 and 63 Pupil Iris activity reflects physiological reactions to different sensory stimuli, resulting in a variation in pupil size. As such, pupillometry is a method that can provide valuable data concerning the functioning of the autonomous nervous system.64 Pupil size reflects the interaction between the sympathetic and parasympathetic divisions of the autonomic nervous system and can be used to evaluate brainstem function in comatose patients.65 Noxious stimulation and the cold pressure test dilate the pupil—pupillary reflex dilatation (PRD)—in both unanaesthetised and anaesthetised humans.66 In the absence of anaesthesia, dilatation is primarily mediated by the sympathetic nervous system. In contrast, under anaesthesia, pupillary dilatation in response to noxious stimulation or desflurane step-up is mediated principally by inhibition of the midbrain parasympathetic nucleus, although the exact mechanism remains unknown.67 PRD is not present in organ donors (Yang). In addition, esmolol does not block PRD in anaesthetised volunteers.68 Pupillary size and reactivity have long been a critical component of the clinical assessment of patients with or without neurological disorders.69 Neuromuscular blocking drugs do not alter the pupillary light reflex.70 Infrared pupillary scans have been used extensively as an objective measure of pupillary reflexes during pharmacological studies on human subjects.71 Women show greater pupillary dilatation than men, this gender difference in pain perception being beyond voluntary control and reflecting low-level sensory and/or affective components of pain.11 Pupillometry has served to assess the bioavailability of rectal and oral methadone in healthy subjects72, as well as, for example, the influence of age or cytochrome P4503A activity on the acute disposition and effects of oral transmucosal fentanyl citrate.73 and 74 Pupillometry is also able to quantify the extent and time course of the effects of morphine-6-glucuronide.75 Similarly, the pharmacodynamics of epidural alfentanil, fentanyl and sufentanil have been studied with this method.76 and 77 Dynamic pupillometry with automatic recording has recently been developed.78 and 79 PRD is measured using an ophthalmic ultrasound biomicroscope (Oasis Colvard Pupillometer) or video-based pupillometer (Procyon video pupillometer, FIT 2000, videoalgoscan). The pupillary response to noxious stimulation induced by electrical fingertip stimulation was investigated in volunteers by Chapman et al.80 These authors found that PRD began at 0.33 seconds and peaked at 1.25 seconds after the stimulus. PRD increased significantly in peak amplitude as the intensity of the stimulus increased. Larson et al showed that alfentanil exponentially impaired the PRD, decreasing the maximum response amplitude from 5 mm at 0 ng/ml, to 1.0 mm at 50 ng/ml, and to 0.2 mm at 100 ng/ml.81 In contrast, alfentanil administration had no effect on the pupillary light reflex. Dilatation of the pupil in response to a noxious stimulus is a measure of opioid effect, and this stimulus-induced pupillary dilatation may be used to evaluate the analgesic component of a combined volatile and opioid anaesthetic. The relative variations of PRD (+233%) are more sensitive than those of heart rate (+19%) or arterial pressure (+13%) after an electrical stimulus (65–70 mA, 100 Hz) has been applied to the skin of the abdominal wall.68 During anaesthesia, PRD allows an estimation of the sensory level during combined general/epidural anaesthesia in adults.82 The supraspinal effects of epidural fentanyl can be assessed during general anaesthesia using infrared pupillometry, maximum suppression being 70±15% for the epidural route and 96±3% for the intravenous route.83 In children, a PRD of 0.2 mm is sensitive to the loss of analgesia.84 PRD during anaesthesia is not initiated by slowly conducting C fibres, and fentanyl at 3 μg/kg depresses the reflex.85 During propofol anaesthesia in healthy patients, the fall in PRD is a better measure of the progressive increase in effect of a remifentanil concentration up to 5 ng/ml than are haemodynamic measures or the bispectral index (BIS). Pupil dilatation in response to 100 Hz tetanic stimulation decreased progressively from 1.55 (0.72) to 0.01 (0.03) mm as remifentanil concentration increases.86 Similar responses have been found also in children by Constant et al.87 Quantitative pupillary measurements can be reliably obtained during anaesthesia with newer pupillometers. Continuous improvements are seen in the flexibility and recording capacity of pupillometers, and they are used in an increasing number of medical fields, including anaesthesiology. The limitations of this method are that droperidol and metoclopramide constrict the pupil and block the pupillary dilatation brought about by nociceptive stimuli, whereas ondansetron does not. Larson recommends that when pupillary diameter measurements are used to gauge opioid levels during experimental conditions or during surgical anaesthesia, antiemetic medication acting on the dopamine D2 receptor should be avoided.88 Clonidine also modifies the central norepinephric control of pupillary function.89 Autonomic neuropathies and spinocerebellar degeneration syndromes are strongly associated with pupillary abnormality, both at rest and in tonic conditions, and may disturb monitoring. Ocular microtremor Ocular microtremor is a physiological tremor whose frequency is related to the functional status of the brainstem. It is suppressed by propofol and sevoflurane in a dose-dependent manner. Sevoflurane and ocular microtremor accurately predict response to verbal command.90 Ocular microtremor may be a useful monitor of depth of hypnosis, but further studies are needed despite encouraging results in the evaluation of preoperative analgesia.91 Spontaneous EEG The effects of noxious stimulation on the EEG have long been studied to monitor cerebral function.92 The basic EEG responses to noxious surgical stimulation have not been clearly defined, which has been a major factor limiting the clinical use of the EEG to monitor anaesthesia. Bispectral index The BIS is a statistical index involving the weighted average of three subparameters that analyse the phase and frequency relations between the component frequencies in the EEG.93 It changes with increasing concentration of anaesthetic agents and is correlated with sedation scales. The BIS correlates well with the hypnotic component of anaesthesia but predicts movement in response to surgical stimulation less reliably, especially when different combinations of hypnotic and analgesic drugs are used. Use of the BIS has been shown to prevent awareness in at-risk patients.94 Early studies with the BIS show that it could be a useful predictor of whether patients will move in response to skin incision during anaesthesia with isoflurane/oxygen or propofol/nitrous oxide and no opioid.95 and 96 Leslie et al97 have compared several parameters in 10 propofol-anaesthetised volunteers and determined their prediction probability of movement. The BIS (PK=0.86), 95% spectral edge frequency (PK=0.81), pupillary reflex amplitude (PK=0.74) and systolic arterial blood pressure (PK=0.78) did not differ significantly from those of a modelled propofol effect-site concentration (PK=0.76). In a study of 60 unpremedicated adults98, a BIS of 60 separated patients responding to laryngeal mask airway insertion from non-responders (P=0.006), with a sensitivity of 68% and a specificity of 70%. Movement response was not predicted by cardiovascular changes. Sebel et al, in a multicentre study, pointed out that, when opioid analgesics were used, the correlation to patient movement became much less significant, so that patients with apparently ‘light’ EEG profiles could not move or otherwise respond to incision. Therefore, the adjunctive use of opioid analgesics confounds the use of BIS as a measure of anaesthetic adequacy when movement responses to skin incision99 or to another noxious test100 are used. BIS and sevoflurane end-tidal concentration are reliable guides to the depth of sedation, with prediction probability values of 0.966 and 0.945, respectively, but not to the adequacy of anaesthesia for preventing movement.101 In a same way, Doi et al102 have shown that the auditory evoked potential (AEP) index discriminated between movers and non-movers with a prediction probability of 0.872. BIS, spectral edge frequency and median frequency could not predict movement at laryngeal mask airway insertion in patients anaesthetised with propofol and alfentanil. The addition of remifentanil to propofol affected the BIS only when a painful stimulus was applied.103 Moreover, remifentanil attenuated or abolished increases in BIS and MAP after tracheal intubation in a comparable dose-dependent fashion. In another study with sevoflurane104, the prediction probability values for AEP index, BIS and sevoflurane concentration for sedation score were 0.820, 0.805 and 0.870, respectively, indicating a high predictive performance for depth of sedation. AEP index and sevoflurane concentration successfully predicted movement after skin (prediction probability 0.910 and 0.857, respectively), whereas BIS did not (prediction probability 0.537). Despite these limitations, BIS might be a useful clinical monitor for predicting patient movement to command during the intraoperative wake-up test in scoliosis surgery105, particularly when controlled hypotension is used and haemodynamic responses to the emergence of anaesthesia are blunted. There are, however, various limitations of the BIS. Vivien et al pointed out the fact that the fall in BIS following the administration of myorelaxant was significantly correlated to the BIS.106 During fentanyl-induced muscular rigidity, BIS recordings reflect EMG variations. When assessing BIS in the absence of neuromuscular blockade, it is necessary to evaluate the effect of the electromyelogram (EMG) on the BIS before making conclusions about depth of sedation. Fentanyl-induced rigidity appears to be a dose-related phenomenon that an EMG variable of BIS 3.4 is able to quantify.107 It must be borne in mind that BIS is primarily a sedation monitor. Entropy Entropy is a quantitative measure used to determine the disorder or randomness in a closed system, in the sense of thermodynamic/metabolic processes or the increasing molecular disorder in a structure, according to Boltzmann's definition of entropy (S) S=k ln(Ω). The second law of thermodynamics states that the entropy (and disorder) increases as time moves forward. Shannon has extended this concept to information theory and defines entropy in terms of a discrete random event x, with possible states 1,…,n as: H(x)=−Sumi(p(i)log(p(i)). There are multiple ways in which to compute the entropy of a signal: in a time domain, as approximate entropy108 and 109 or as Shannon entropy.110 In the frequency domain, spectral entropy may be computed; this is the case for the Datex-Ohmeda Entropy Module, a new EEG monitor designed to measure depth of anaesthesia.111 The monitor calculates a ‘state entropy’, computed over the frequency range 0.8–32 Hz, and a ‘response entropy’, computed over the frequency range 0.8–47 Hz. The difference between the response and state entropies is a reflection of the high-frequency activity of the EEG, and includes by nature some EMG-frequency components. Some studies with this monitor have now been published. It appears that it has the same lack of sensibility as the BIS when analgesics drugs are used, for example with ketamine112 or nitrous oxide.113 An elevated difference between response entropy and state entropy is related to a significant increase in state entropy, blood pressure and heart rate, response entropy during painful stimulation is seen more often in patients anaesthetised with 0.8% compared with 1.4% isoflurane. Response entropy more probably reflects the frontal EMG and may be useful to identify inadequate anaesthesia and patient arousal during painful stimulation.114 Vanluchene et al115 compared state entropy, response entropy and BIS when measuring loss of response to verbal command (LOR(verbal)) and noxious stimulation (LOR(noxious)) during propofol infusion with and without remifentanil. BIS, state entropy and response entropy all detected LOR(verbal) accurately, but BIS performed better at 100% sensitivity. The sensitivity/specificity for the detection of LOR(verbal) decreased for all methods with increasing Ce(REMI). LOR(noxious) was poorly described by all measures. Future studies are needed to elucidate the role of response entropy in terms of analgesia monitoring. Evoked EEG Animal and human cerebral evoked potentials have been employed for years in pain research to describe pain perception physiology and to test the effectiveness of various analgesics.116 and 117 More recently, positron emission tomography has revealed significant changes in pain-evoked activity within multiple cerebral regions, particularly the anterior cingulate cortex.118 Subdivision of the anterior cingulate cortex into an anterior non-specific attention/arousal system and a posterior pain system explain the interaction between alertness and pain.119 Mid-latency AEPs are small changes noted on the EEG that are caused by discrete auditory stimuli. AEPs are more sensitive to pain stimuli than are spectral features of the spontaneous EEG120 or BIS.102 The A-Line Auditory Evoked Index (AAI) is a unique device commercially available for depth of anaesthesia monitoring. Values of the index range between 0 and 100, but there is a wide variation in the awake values and a considerable overlap of AAI values between consciousness and unconsciousness, suggesting that further improvement of the AAI system is required.121 and 122 Unlike AEPs, because of the variability in latency and the difficulties of repeating stimulation, somatosensory evoked cerebral potentials are analysed by calculating the spectral power in selected frequency bands and frequency percentiles from the spontaneous EEG segment preceding each somatosensory stimulus. Late cortical somatosensory evoked potentials response parameters are calculated from the respective post-stimulus EEG segments. Spectral analysis of the late cerebral (later than 80 milliseconds) components of the potential evoked by painful somatosensory stimuli reveals a stimulus-induced increase of power in the low frequencies—delta and theta. The pre-stimulus:post-stimulus relationship of the delta waves was found to be the most sensitive measure for monitoring the cerebral bioavailability of meperidine.123 Under halothane anaesthesia, late somatosensory evoked potentials and haemodynamic responses in response to painful electrical stimuli are abolished by fentanyl.124 The same authors showed that the analgesic effect of low-dose ketamine (0.25 and 0.5 mg/kg) could be quantified by somatosensory evoked potentials, especially by a dose-dependent decrease of the long-latency N150-P250 somatosensory-evoked late cortical response.125 Laser-evoked potentials are nociceptive-related brain responses to activation of the cutaneous nociceptors by laser radiant heat stimuli. The cost of the technique is the major limitation to its development. Monitoring analgesic administration The computer administration of opioids by target-controlled infusion contributes to the monitoring of analgesia.126 and 127 Real-time displays of intravenous anaesthetic concentrations and effects could significantly enhance intraoperative clinical decision-making by a visualisation of pharmacodynamic relationship between hypnotics and analgesics.128 Titration of opioids during noxious events The majority of clinical studies have focused on the BIS. Brocas et al showed that an alfentanil bolus of 15 μg/kg markedly reduced the increase in BIS values, blood pressure and heart rate observed immediately after tracheal suction, whereas there are differences in Ramsay scores.129 Godet et al showed that maintenance of anaesthesia predominantly with propofol and a low dose of remifentanil, administered in accordance to the BIS, was associated with a greater stability in perioperative haemodynamics.130 Likewise, sufentanil effect-site concentrations adjusted on BIS values and variations could achieve good haemodynamic tolerance.127 In cardiac patients, titration of propofol using the BIS allows a significant reduction in propofol consumption, with only minor effects on the stress response in these conditions.131 Considerations of stability Analgesia is a stable state seen both during and after a noxious stimulus. One of the questions of importance here is the definition of stability. For example, a system is stable if it can maintain equilibrium after stimulation, and adequate analgesia could be defined in terms of resistance to change. In control theory, stability characterises the reaction of a dynamic system to external influences. Likewise, haemodynamic stability is often defined by a lack of variation between 20% under or upper reference heart rate or arterial pressure. This percentage is guided by experience and can be changed if a more stable state is required. Absolute or relative percentages of variation, coefficients of variation, standard deviations and ranges are parameters available to describe stability. Variations in statistical significance are not always of great clinical use. Analgesia is a temporal state and must always be topped up against a background of duration and intensity of stimulation. Conclusion If information collected from the EEG response entropy, heart rate and pulse plethysmography of anaesthetised patients is combined, a significantly improved classification performance (96%) between movers and non-movers to skin incision is achieved compared with discrimination using any single variable alone. This suggests that a combination of information from different sources may be necessary for monitoring the level of nociception during anaesthesia.59 Pupillometry seems to be a promising generalised tool, but we must aware of being too enthusiastic towards it because there are commercially available analgesia monitors who no longer still exist.132 Many candidate signs are available for analgesia monitoring (Table 3). But whatever the latest monitors are like133 and 134, they will never be able to predict whether the depth of analgesia is sufficient for the next painful surgical stimulus: they can only monitor the anaesthetic state at the time of measurement, and the balance between excitation and responsiveness. Anaesthetists must always consider their experience ahead of any technique for monitoring the depth of analgesia. Table 3. Different parameters available for monitoring analgesia. Parameter to be monitored Clinical scales PRST score Sedation scores Effect of pain Sympathetic system Direct microneurography Heart rate variability Spectral analysis of heart rate Low-frequency/high-frequency power ratio Arterial blood pressure Skin vasomotor reflexes: laser Doppler flowmetry Plethysmogram amplitude, notch amplitude Pulse transit time Ventilation Respiratory rate Pupil Pupillary reflex dilatation Brainstem Ocular microtremor Spinal Movement Cerebral Response entropy Auditory evoked potentials Somatosensory evoked potentials Spectral analysis of late cerebral potential components Bispectral index Action of analgesics Plasma concentration Theoretical concentrations with target-controlled infusions Secondary effects: heart rate, respiratory rate Action of anaesthetics End-tidal concentrations of inhaled anaesthetics Theoretical concentrations of intravenous drug Multiparametric approaches are probably the best way to deal with monitoring analgesia.135 Like Kutas and Federmeier136, we could say that a combination of measures—old and new, central and peripheral—will ultimately provide the greatest power to resolve the questions we hope to answer, using all the physiological measures at our disposal, in our quest to understand the nature of the relationship between mind and body, between analgesia and anaesthesia.(Box 1) Research agenda • characterise the mechanisms of pain perception • characterise the mode of action of analgesics • characterise individual variations in and intervariability of events related to noxious stimuli • develop plethysmography-derived and pupillary reflex indices • include the pharmacodynamics of hypnotics/analgesics in EEG automated depth of anaesthesia systems • develop data-fusion systems and multimodal monitoring of analgesia References 1 C. 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Hello Everyone, Here's an interesting article on succs vs Roc. in RSI with an even more interesting reply... HTH, ACE844 (© 2005 by International Anesthesia Research Society. Volume 101(5) @ November 2005, pp 1356-1361 Rocuronium Versus Succinylcholine for Rapid Sequence Induction of Anesthesia and Endotracheal Intubation: A Prospective, Randomized Trial in Emergent Cases [Anesthetic Pharmacology) Sluga, Mathias MD; Ummenhofer, Wolfgang MD; Studer, Wolfgang MD; Siegemund, Martin MD; Marsch, Stephan C. MD, DPhil Department of Anesthesia, Krankenhaus Thusis, Switzerland Accepted for publication April 21, 2005. Address correspondence to Stephan Marsch, MD, DPhil, Medizinische Intensivstation, Kantonsspital, 4031 Basel, Switzerland. Address e-mail to smarsch@uhbs.ch.] Abstract When anesthesia is induced with propofol in elective cases, endotracheal intubation conditions are not different between succinylcholine and rocuronium approximately 60 s after the injection of the neuromuscular relaxant. In the present study, we investigated whether, in emergent cases, endotracheal intubation conditions obtained at the actual moment of intubation under succinylcholine differ from those obtained 60 s after the injection of rocuronium. One-hundred-eighty adult patients requiring rapid sequence induction of anesthesia for emergent surgery received propofol (1.5 mg/kg) and either rocuronium (0.6 mg/kg; endotracheal intubation 60 s after injection) or succinylcholine (1 mg/kg; endotracheal intubation as soon as possible). The time from beginning of the induction until completion of the intubation was shorter after the administration of succinylcholine than after rocuronium (median time 95 s versus 130 s; P < 0.0001). Endotracheal intubation conditions, rated with a 9-point scale, were better after succinylcholine administration than after rocuronium (8.6 ± 1.1 versus 8.0 ± 1.5; P < 0.001). There was no significant difference in patients with poor intubation conditions (7 versus 12) or in patients with failed first intubation attempt (4 versus 5) between the groups. We conclude that during rapid sequence induction of anesthesia in emergent cases, succinylcholine allows for a more rapid endotracheal intubation sequence and creates superior intubation conditions compared with rocuronium. -------------------------------------------------------------------------------- A rapid sequence induction of anesthesia and endotracheal intubation are indicated in emergency situations in the presence of a full stomach or other conditions with an increased risk of aspiration. Traditionally, succinylcholine has been the neuromuscular blocking drug of choice for rapid sequence induction of anesthesia. However, as a result of its depolarizing effect, succinylcholine can have serious side effects and is contraindicated in many conditions. Rocuronium has the most rapid onset of the currently available nondepolarizing neuromuscular blocking drugs. Therefore, many studies have investigated whether rocuronium may be a suitable alternative to succinylcholine. A meta-analysis of the Cochrane collaboration concluded that when propofol is used to rapidly induce anesthesia, endotracheal intubation conditions are not statistically different between succinylcholine and rocuronium (1). Before applying this evidence in daily practice, some important limitations of the Cochrane Review have to be recognized: (a) most of the patients receiving propofol were elective cases; ( only a small number of emergent cases actually underwent a rapid sequence induction of anesthesia and endotracheal intubation with propofol and rocuronium; and © in most studies included in the meta-analysis, tracheas were intubated approximately 60 s after the injection of the neuromuscular blocking drug, yet clinical practice may allow intubation sooner than 60 s after the injection of succinylcholine. It is currently not known whether endotracheal intubation conditions obtained at the actual moment of intubation under succinylcholine differ from those obtained 60 s after the injection of rocuronium. Accordingly, the aim of the present study was to compare rocuronium with the current practice of the use of succinylcholine (i.e., endotracheal intubation as soon as possible) in patients requiring rapid sequence induction of anesthesia and endotracheal intubation for emergent surgery. The hypotheses to be tested were that (a) succinylcholine would allow for an earlier completion of the endotracheal intubation sequence and ( succinylcholine would create superior intubation conditions at the actual time of intubation. Methods The study took place in the Hospital of Thusis, a rural Level III center. All adult (age, >=18 yr) patients undergoing emergent surgery under general anesthesia were eligible. Indications for emergent surgery were mainly trauma (the hospital is located in a tourist region with skiing accidents in winter and climbing accidents in summer) and laparotomies. Exclusion criteria were hyperkalemia, neurologic disorders, burns, familial history of malignant hyperthermia, cesarean delivery, complications during birth before delivery, known or anticipated difficult endotracheal intubation warranting awake fiberoptic intubation, contraindication against the use of propofol (e.g., shock) and allergy to rocuronium. The study was approved by the regional Ethics Committee, and written informed consent was obtained during the preoperative visit. The primary outcomes of the study were the duration of the endotracheal intubation sequence and intubation conditions. Using a 9-point grading system for intubation conditions (Table 1), a difference of at least 1.0 points was considered to be of clinical relevance. A power analysis revealed that 85 patients were required for each study group to detect that difference with a power of 0.9 and a two-sided [alpha] of 0.05. To account for protocol violations related to an emergent procedure, we planned to enroll 90 patients per group. -------------------------------------------------------------------------------- [Help with image viewing] [Email Jumpstart To Image] Table 1. Scoring System for Endotracheal Intubation Conditions -------------------------------------------------------------------------------- Patients were randomly allocated (sealed envelopes) to receive either 0.6 mg/kg of rocuronium (Esmeron™, Organon, Switzerland) or 1.0 mg/kg of succinylcholine (Lystenon™, Nycomed, Switzerland) as the neuromuscular blocking drug. No premedication was administered. Upon arrival in the operating room, a 18-gauge cannula was inserted in a forearm vein. Routine monitoring was used. End-tidal carbon dioxide was measured using the side-stream method (Cardiocap, Datex, Finland). Electrodes of a nerve stimulator (Healthcare NS 272; Fisher & Paykel, New Zealand) were placed over the left ulnar nerve. One of three experienced staff anesthesiologists (MS, WU, or SM), assisted by a registered anesthetic nurse and a scrub nurse, was present throughout the whole procedure, guided the injection of drugs, and performed the endotracheal intubation. The staff anesthesiologist was not blinded to the neuromuscular blocking drug used, and the management of difficulties and complications, if any, was left to his discretion. To minimize bias, intubations were performed by three different anesthesiologists who had no personal preference for one of the two neuromuscular blocking drugs. The endotracheal intubation sequence was defined as time interval between the injection of propofol and the first appearance of end-tidal carbon dioxide on the screen of the monitor. After 3 min of the administration of oxygen, cricoid pressure was applied, and anesthesia was induced with fentanyl 2 µg/kg and propofol 1.5 mg/kg. The neuromuscular blocking drug was injected as soon as the eyelid reflex had disappeared, and the nerve stimulator was switched to the single-twitch mode (rate, one twitch per second). Laryngoscopy was started either after the cessation of fasciculations in the lower extremities (2), if any, the cessation of a visible motor response to continuous single-twitch nerve stimulation, or after 50 s (anticipated time of intubation 60 s after the injection of the neuromuscular blocking drug), whichever was earlier. Endotracheal intubations were performed using a Macintosh size 3 blade and a tracheal tube (Mallinckrodt Hi-Contour, Mallinckrodt, Ireland) with an internal diameter of 7.5 cm in women and of 8.5 cm in men. The timing of events was performed by the anesthetic nurse. Intubation conditions are usually evaluated using the following factors: (a) ease of laryngoscopy, ( position and movement of the vocal cords, and © response to intubation of the airway and the limbs (3). However, previous studies differ in that either a numerical (1) or a qualitative (4) score was derived from these factors. To allow for a comparison with both types of scoring systems previously used, we provide both a numerical and a qualitative rating. Both ratings are based on a scoring system proposed for good clinical research practice in studies of neuromuscular blocking drugs (3). The intubating anesthesiologist rated the ease of laryngoscopy, the movement and position of the vocal cords, and the reaction to intubation, as demonstrated in Table 1. Desaturation was defined as either a saturation <=90% or a decrease in saturation of >=5% occurring at any time between the start of the induction sequence and 3 min after the completion of the intubation. Data, presented as mean ± sd unless otherwise stated, were analyzed using SPSS 12.0 for Windows, a commercially available statistical software (SPSS, Chicago, IL). Two-way analysis of variance, unpaired Student’s t-test, Mann-Whitney test, Fisher’s exact test, and the logrank test were applied, as appropriate. General linear modeling was used to assess differences among the 3 intubating anesthesiologists with regard to scoring of the intubation conditions. A P < 0.05 was considered to represent statistical significance. Results During the study period ending with the completion of the protocol in the 180th patient, 234 consecutive patients underwent emergency surgery under general anesthesia. Five had to be excluded because of predefined exclusion criteria (2 cesarean delivery, 2 hemorrhagic shock, and 1 hyperkalemia), 16 refused to participate, and the enrollment of 33 was missed, mainly because of high workload. One-hundred-eighty patients were randomized, received the allocated treatment, and were included in the analysis (Table 2). -------------------------------------------------------------------------------- [Help with image viewing] [Email Jumpstart To Image] Table 2. Patient Demographics -------------------------------------------------------------------------------- The median time interval between the beginning of the administration of propofol and the disappearance of the eyelid reflex was 30 s (interquartile range, 18.5 s) in the succinylcholine group and 26 s (interquartile range, 20 s) in the rocuronium group (P = 1.0). Figure 1 depicts the time interval from injection of the neuromuscular blocking drug to the cessation of a visible motor response to continuous single-twitch nerve stimulation of the ulnar nerve. This time interval was significantly shorter (P < 0.0001) in the succinylcholine group (median time, 40 s) compared with the rocuronium group (median time, 70 s). Figure 2 depicts the time interval between the beginning of the administration of propofol and the first appearance of end-tidal carbon dioxide after endotracheal intubation, which was significantly shorter (P < 0.0001) in the succinylcholine group (median time, 95 s) compared with the rocuronium group (median time, 130 s). -------------------------------------------------------------------------------- [Help with image viewing] [Email Jumpstart To Image] Figure 1. Kaplan-Meyer curve of the probability of the disappearance of a visible motor response to a continuous single-twitch stimulation of the ulnar nerve after injection of succinylcholine or rocuronium. Time 0 denotes the injection of the neuromuscular blocking drug. Curves differ significantly (P = < 0.0001; logrank test). -------------------------------------------------------------------------------- -------------------------------------------------------------------------------- [Help with image viewing] [Email Jumpstart To Image] Figure 2. Kaplan-Meyer curve of the probability of the completion of the endotracheal intubation sequence including succinylcholine or rocuronium as the neuromuscular blocking drug. Time 0 denotes the beginning of the injection of the induction drug propofol. The endotracheal intubation sequence was defined to be completed upon the first appearance of end-tidal carbon dioxide after intubation. Curves differ significantly (P < 0.0001; logrank test). -------------------------------------------------------------------------------- Scores for endotracheal intubation conditions were significantly higher in the succinylcholine group than in the rocuronium group (8.6 ± 1.1 versus 8.0 ± 1.5; P < 0.001). This difference resulted almost exclusively from a difference in the subscore rating the response to intubation (2.8 ± 0.5 versus 2.3 ± 1.0; P < 0.0001), whereas there was no difference in the subscores for laryngoscopy (2.9 ± 0.3 versus 2.9 ± 0.3; P = 0.91) and vocal cords (2.9 ± 0.4 versus 2.8 ± 0.6; P = 0.23). Figure 3 depicts the scores for intubating conditions. Note that compared with the rocuronium group, there were significantly more excellent intubation conditions in the succinylcholine group (Fig. 3). However, there was no difference in patients with poor intubation conditions between the groups (7 versus 12; P = 0.33). General linear modeling showed (a) no significant difference among the 3 intubating anesthesiologists with regard to the rating of the intubation conditions (F2,168 = 0.21; P = 0.81), ( no significant interaction of the 2 between-subject factors intubating anesthesiologist and neuromuscular blocking drug (F2,168 = 1.47; P = 0.23), and © no significant interaction of the between-subject factor intubating anesthesiologist and the within-subject factor subscores of intubation conditions (F4,336 = 0.87; P = 0.48). This indicates that there was no systematic difference in scoring among the 3 intubating anesthesiologists. -------------------------------------------------------------------------------- [Help with image viewing] [Email Jumpstart To Image] Figure 3. Endotracheal intubation conditions during rapid sequence induction of anesthesia and endotracheal intubation with succinylcholine or rocuronium as the neuromuscular blocking drug. The scoring system is explained in Table 1. *P < 0.05 between the 2 neuromuscular blocking drugs (Fisher’s exact test). -------------------------------------------------------------------------------- Eighty-six of 90 patients in the succinylcholine group and 85 of 90 patients in the rocuronium group were intubated during the first attempt (P = 1.0). All remaining nine patients were successfully endotracheally intubated in the second attempt. The reasons for the four failures of the first intubation attempt in the succinylcholine group were one poor intubation condition (numerical score 3), one esophageal intubation (intubation score excellent), and two “difficult anatomy” (intubation scores excellent and good, respectively) that could be mastered in the second attempt by mounting the tube on a stylet. The reasons for the five failures of the first intubation attempt in the rocuronium group were one poor intubation condition (numerical score 4), two esophageal intubations (intubation scores excellent and good, respectively), and two “difficult anatomy” (intubation score excellent in both cases) that could be mastered in the second attempt by mounting the tube on a stylet. Thus, poor intubation conditions were observed in only two of the nine patients (one in each group) not intubated in the first attempt. A desaturation occurred in 5 of 90 patients in the succinylcholine group and in 9 of 90 patients of the rocuronium group (P = 0.40). Poor endotracheal intubation conditions were observed in only 2 of the 14 patients (one in each group) with desaturation, whereas 8 of 14 desaturations were associated with an excellent intubation score. Four of 14 desaturations (2 in each group) occurred in patients with a second intubation attempt. Compared with the patients without desaturation, the time interval from the beginning of the administration of propofol and the completion of the intubation was longer in patients with desaturation (134 ± 9 s versus 116 ± 3 s; P = 0.047). Discussion In the present study, we compared rocuronium with the current practice of the use of succinylcholine (i.e., endotracheal intubation as soon as possible) in patients requiring rapid sequence induction of anesthesia and endotracheal intubation for emergent surgery. When succinylcholine was used as the neuromuscular blocking drug for rapid sequence induction of anesthesia, the median intubation sequence was 35 s shorter than when rocuronium was used. Succinylcholine created excellent intubation conditions more often than rocuronium, and there was a statistically significant difference of 0.5 points on a 9-point grading scale of intubation conditions in favor of succinylcholine. However, as far as clinically acceptable intubating conditions and failed intubation attempts are concerned, the two relaxants were not statistically different. Analyzing the available evidence up to the year 2000, a Cochrane Review concluded that for rapid sequence induction of anesthesia, succinylcholine created superior endotracheal intubation conditions to rocuronium when comparing excellent intubation conditions. Using the less stringent clinically acceptable intubation conditions, the two drugs were not statistically different (1). Moreover, based on a subgroup analysis, the Cochrane Review concluded that intubation conditions did not statistically differ between the administration of succinylcholine and rocuronium when propofol was used as the drug to induce anesthesia (1). Several potential limitations of these conclusions are noteworthy. Only 24 of the 1606 patients included in the Cochrane Review were emergent cases that actually underwent a true rapid sequence induction of anesthesia and endotracheal intubation with both propofol and rocuronium. All 24 patients were part of a single study and received 1 mg/kg of rocuronium (4). Moreover, only 47 of the 640 patients included in the subgroup using propofol as the induction drug (4–12) were emergency cases undergoing a true rapid sequence induction of anesthesia and endotracheal intubation. From the remaining 593 elective cases, approximately 50% (n = 290) did not undergo a true rapid sequence induction of anesthesia. Most previous studies comparing succinylcholine and rocuronium assessed endotracheal intubation conditions approximately 60 seconds after the injection of the neuromuscular blocking drug (1). Whereas this is an appropriate time interval for rocuronium, a delay between injection of succinylcholine and start of laryngoscopy of 50 seconds or more does not reflect current practice; most, if not all, anesthesiologists choosing succinylcholine for rapid sequence induction of anesthesia and endotracheal intubation take advantage of its rapid onset of action and start laryngoscopy as quickly as possible, i.e., after the cessation of fasciculations. Indeed, 50 seconds after the injection of the neuromuscular blocking drug, i.e., the time of the beginning of the laryngoscopy in previous studies, the intubation sequence was already completed in more than one-third of the patients in the succinylcholine group of the present study. Based on current evidence, the induction of anesthesia sequence of the present study was chosen to achieve the best possible endotracheal intubation conditions for the rocuronium group. Propofol was used as the induction drug because this anesthetic seems to be superior to all other drugs with regard to intubating conditions after rocuronium injection (1). Fentanyl (2 µg/kg) was added to the induction sequence because opioids, in doses equivalent to alfentanil 20 µg/kg, were found to significantly improve intubating conditions after rocuronium administration (13). Intubation was attempted 60 seconds after the injection of rocuronium because this seemed to be the earliest moment when acceptable intubation conditions can be reliably achieved (1). Rocuronium was used in a dose of 0.6 mg/kg because there seemed to be no benefit of larger rocuronium doses on intubation conditions when propofol was used as the induction drug (1). Previous work demonstrated a dose-dependent effect of rocuronium on both onset and duration of neuromuscular block (14). Thus, there is the possibility that larger doses of rocuronium would allow for an earlier intubation. However, all studies comparing intubation conditions after different doses of rocuronium did so after a predefined time interval (usually 60 seconds after the injection of rocuronium). Thus, it is unknown whether the earlier onset of neuromuscular block associated with doses larger than 0.6 mg/kg of rocuronium would translate into a clinical advantage, i.e., the possibility for an earlier intubation with at least the same intubation conditions that are achievable at 60 seconds. An important limitation of our study is the lack of a double-blind design. Concealing the effects of drugs that have visible effects such as fasciculations is inherently difficult. Moreover, because the two neuromuscular blocking drugs studied differ in onset time, awareness of the time of the injection of the drug results in unblinding. Thus, a perfect double-blind design implies that the intubating anesthesiologist is not able to see or overhear the patient and the team performing the induction sequence and is immediately available to intubate the patient’s trachea after the cessation of fasciculations. A rapid sequence induction of anesthesia is a high-risk procedure requiring the full attention of an appropriately trained anesthesiologist. Because, in our settings, the simultaneous achievement of perfect blinding and optimal patient safety was not feasible, we opted for a single-blind study design. The statistical analysis of the effects and interactions of neuromuscular blocking drugs and the intubation scores revealed a homogenous rating with no systematic differences among the anesthesiologists performing the intubations. The power of the present study was too small to allow reliable conclusions on the incidence of complications. These issues should be addressed in large multicenter trials. Interestingly, in the present study, only a minority of failed first endotracheal intubation attempts and desaturations were associated with a low score of intubation conditions. If confirmed in further trials, these findings may lead to a modification of the scoring system presently used. What are the practical implications of our findings? Choosing rocuronium instead of succinylcholine for rapid sequence induction of anesthesia prolongs the time of unprotected airway, i.e., the time interval from beginning of the induction until completion of endotracheal intubation, from a median time of 95 seconds to a median time of 130 seconds. The additional risk of aspiration and desaturation resulting from a prolongation of the intubation sequence by a median time of 35 seconds is unknown, but it is most likely very small in most patients. However, patients with an especially high risk for aspiration or a desaturation may benefit from a more rapid intubation. Choosing rocuronium instead of succinylcholine for rapid sequence induction of anesthesia results in less optimal intubating conditions. However, the difference between the two relaxants is small and mainly results from lower ratings in the subscore addressing the reaction to intubation, i.e., coughing or bucking. Because the reaction to intubation occurs after the placement of the tube, the relevance for patients’ safety is marginal. Until more data on complications are available, we suggest that anesthesiologists select the best treatment for their patients undergoing a rapid sequence induction of anesthesia on an individual basis by balancing intubation conditions and duration of the intubation sequence against potential side effects. Compared with the subgroup of patients receiving propofol included in the recent Cochrane Review on rapid sequence induction (1), in the present study, we observed significantly more poor intubation conditions after both neuromuscular blocking drugs (19 of 180 versus 27 of 640 poor intubation conditions; P = 0.007). Because most patients included in the Cochrane Review were elective cases not undergoing a true rapid sequence induction of anesthesia, this difference is most likely explained by differences in the patient population and the procedure. Although elective cases are valuable models for investigating the effects of neuromuscular blocking drugs, findings obtained in this setting may thus not be necessarily extrapolated to emergency situations. In conclusion, in the context of a rapid sequence induction of anesthesia with propofol and fentanyl in emergent cases, succinylcholine allowed for a more rapid endotracheal intubation sequence and created superior intubation conditions than rocuronium. Presently, practitioners have to balance the quality of intubation conditions and the duration of the intubation sequence against the potential for side effects. Large-scale trials are required to address important safety issues such as failed intubation attempts and desaturations associated with the use of succinylcholine or rocuronium. References 1. Perry J, Lee J, Wells G. Rocuronium versus succinylcholine for rapid sequence induction intubation. In: The Cochrane Library. Issue 3. Hoboken, NJ: John Wiley & Sons, Ltd., 2004. [Context Link] 2. Ummenhofer WC, Kindler C, Tschaler G, et al. Propofol reduces succinylcholine induced increase of masseter muscle tone. Can J Anaesth 1998;45:417–23. 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SFX Bibliographic Links Library Holdings [Context Link] 7. Latorre F, Stanek A, Gervais HW, Kleemann PP. Intubation requirements after rocuronium and succinylcholine. Anasthesiol Intensivmed Notfallmed Schmerzther 1996;31:470–3. SFX Bibliographic Links Library Holdings [Context Link] 8. Le Corre F, Plaud B, Benhamou E, Debaene B. Visual estimation of onset time at the orbicularis oculi after five muscle relaxants: application to clinical monitoring of tracheal intubation. Anesth Analg 1999;89:1305–10. Ovid Full Text Bibliographic Links Library Holdings [Context Link] 9. Naguib M, Samarkandi AH, Ammar A, Turkistani A. Comparison of suxamethonium and different combinations of rocuronium and mivacurium for rapid tracheal intubation in children. Br J Anaesth 1997;79:450–5. SFX Bibliographic Links Library Holdings [Context Link] 10. Puhringer FK, Khuenl-Brady KS, Koller J, Mitterschiffthaler G. Evaluation of the endotracheal intubating conditions of rocuronium (ORG 9426) and succinylcholine in outpatient surgery. Anesth Analg 1992;75:37–40. SFX Bibliographic Links Library Holdings [Context Link] 11. Vinik HR. Intraocular pressure changes during rapid sequence induction and intubation: a comparison of rocuronium, atracurium, and succinylcholine. J Clin Anesth 1999;11:95–100. SFX Bibliographic Links Library Holdings [Context Link] 12. Stoddart PA, Mather SJ. Onset of neuromuscular blockade and intubating conditions one minute after the administration of rocuronium in children. Paediatr Anaesth 1998;8:37–40. [Context Link] 13. Sparr HJ, Giesinger S, Ulmer H, et al. Influence of induction technique on intubating conditions after rocuronium in adults: comparison with rapid-sequence induction using thiopentone and suxamethonium. Br J Anaesth 1996;77:339–42. SFX Bibliographic Links Library Holdings [Context Link] 14. Wright PM, Caldwell JE, Miller RD. Onset and duration of rocuronium and succinylcholine at the adductor pollicis and laryngeal adductor muscles in anesthetized humans. Anesthesiology 1994;81:1110–5. SFX Bibliographic Links Library Holdings [Context Link] (Rocuronium in Emergent Intubation [Letters to the Editor) Chamorro, C MD; Romera, M A. MD; Valdivia, M MD Intensive Care Unit; Hospital Universitario Puerta de Hierro; Madrid, Spain; cchamorro.hpth@salud.madrid.org Dr. Marsch does not wish to respond.] To the Editor: The interesting study published by Sluga et al. (1) could be misinterpreted concerning the use of succinylcholine and rocuronium for emergency tracheal intubation. For surgical emergencies (unscheduled emergency operations), there is typically time to obtain serum electrolytes, a medical history, and written informed consent, as happened in Sluga et al.’s study. However, during emergency tracheal intubations in other settings (e.g., shock, trauma) there is no time to assess renal function status, potassium levels, previous neurologic disorders, or whether the patient has had a long period of immobilization. We reviewed the medical records of all patients who required emergency tracheal intubation in our intensive care unit over the course of 1 yr. Thirty-five percent had at least one condition that potentially contraindicated the use of succinylcholine (2). In several cases, succinylcholine may have precipitated the subsequent cardiac arrest. As Sluga et al. observe, rocuronium results in less optimal, but good, intubating conditions compared with succinylcholine. Other authors have reached the same conclusion (3,4). For these reasons we have replaced succinylcholine with rocuronium for emergency tracheal intubation outside of the operating room. In our view, succinylcholine is an obsolete (5) and potentially dangerous drug for intubating patients in settings where one cannot eliminate well-established contraindications to its use. C. Chamorro, MD M. A. Romera, MD M. Valdivia, MD Intensive Care Unit Hospital Universitario Puerta de Hierro Madrid, Spain cchamorro.hpth@salud.madrid.org

Here's an example of why you shouldn't use a large bore suction cath through an NPA (Airway Obstruction Caused by Nasal Airway [Letters to the Editor) Yokoyama, Takeshi DDS, PhD; Yamashita, Koichi MD, PhD; Manabe, Masanobu MD, PhD Department of Anesthesiology and Critical Care Medicine, Kochi Medical School, Nankoku, Japan, yokoyamt@med.kochi-u.ac.jp] To the Editor: We report a case of sudden airway obstruction caused by a nasal airway that slipped into the trachea and the right main bronchus (Fig. 1). An 87-yr-old man presented with disturbance of consciousness (Glasgow Coma Scale score 9) after removal of a hematoma in the brain ventricle under local anesthesia. We inserted a nasal airway with an internal diameter of 6.0 mm to relieve the obstruction. Three days after surgery, we attempted pharyngeal suction through the nasal airway. The tube slipped through his nasal cavity into his trachea. Figure 1. A, A nasal airway (inner diameter, 6.0 mm). B, The distal half of the nasal airway tube occupied the right bronchus, and the proximal half was located in the trachea. A chest radiograph showed the tip of the nasal airway tube in the right main bronchus (Fig. 1). We placed the patient under general anesthesia with halothane in oxygen and removed the nasal airway without difficulty using Jackson’s laryngeal scope and forceps. Takeshi Yokoyama, DDS, PhD Koichi Yamashita, MD, PhD Masanobu Manabe, MD, PhD Department of Anesthesiology and Critical Care Medicine Kochi Medical School Nankoku, Japan yokoyamt@med.kochi-u.ac.jp

Here's another interesting use for this tool... Hope This Helps, ACE844 (Anasthesia & Analgesia © 2005 by International Anesthesia Research Society.Optimization of Endotracheal Tube Cuff Filling by Continuous Upper Airway Carbon Dioxide Monitoring [Technology @ Computing, and Simulation) Efrati, Shai MD*; Leonov, Yuval MD†; Oron, Amir MD‡; Siman-Tov, Yariv DVM§,; Averbukh, Michael MD*; Lavrushevich, Alex MD||; Golik, Ahuva MD* *Department of Medicine A, †Critical Care Unit, ‡Orthopedic Department, §Experimental Research Laboratory, and ||Department of Anesthesia, Assaf Harofeh Medical Center, Zerifin, affiliated to Sackler School of Medicine, Tel-Aviv University, Israel Aspects of this research are disclosed and claimed in Published PCT Patent Application WO 2002/ 076279 A3. The study was supported by Hospitec Corp., the owner of this patent. SE is a shareholder in Hospitec Corp. Accepted for publication April 4, 2005. Address correspondence and reprint requests to Shai Efrati, MD, Department of Medicine A, Assaf Harofeh Medical Center, Zerifin, 70300, Israel. Address e-mail to efratishai@013.net.il.] Abstract Inappropriate cuff filling is responsible for various complications related to the use of an endotracheal tube (ETT). In this study, we evaluated an objective, noninvasive method for continuous assessment of leak around the ETT cuff by monitoring carbon dioxide pressure (Pco2) in the upper airway. Pco2 levels were measured by capnography simultaneously between the ETT cuff and the vocal cords, at the oropharynx, and in the nares of the nose. Cuff filling was regulated by an electronic controller to achieve the minimal pressure needed to prevent CO2 leak. Feasibility of the method was assessed in a human simulator and in a porcine model. Clinical function was evaluated in 60 patients undergoing surgery, comparing the method to the standard anesthesiologist evaluation. Linear correlations were observed between the ETT cuff pressure and Pco2 level in the human simulator (R2 = 0.954, P < 0.0001) and in the porcine model (R2 > 0.98, P < 0.0001). Iodine leak around the ETT cuff, in the porcine model, occurred only when Pco2 levels were >2 mm Hg. In the surgery patients, the mean ETT cuff pressure determined clinically by the anesthesiologist was significantly higher than the optimal cuff pressure assessed by Pco2 (25.2 ± 3.6 versus 18.2 ± 7.8 mm Hg, respectively; P < 0.001). According to these findings, optimal ETT cuff filling pressure can be identified by monitoring Pco2 at the nares or the oropharynx. -------------------------------------------------------------------------------- A critical aspect in management of mechanically ventilated patients is to avoid complications related to inappropriate endotracheal tube (ETT) cuff filling (1–8). An appropriately inflated ETT cuff should achieve isolation of the lower airways, thus reducing the risk of aspiration around the cuff and possible ventilator-associated pneumonia (VAP), which occurs in up to 25% of intensive care unit (ICU) patients (5–9). However, an over-inflated cuff may cause local mechanical complications such as mucosal ulcerations, granulomas, tracheal stenosis, and tracheoesophageal fistulae (1–4). Optimal ETT cuff filling is defined as the minimal pressure required for airway isolation. It is influenced by airway anatomy, cuff location, cuff compliance, size and volume, and by peak inspiratory pressure (10,11). The common clinical practice of optimizing cuff filling by auscultation or by assessing inhaled-exhaled volume difference is imprecise, and evaluating leak by dye infusion is impractical (12–14). Capnographic measurement of carbon dioxide pressure (Pco2) based on infrared absorption has evolved into a commonly used procedure (15). Cyclic changes of Pco2 measured proximal to the ETT cuff can be used to identify gas leakage around the cuff. The purpose of this study was to establish an accurate, objective, noninvasive bedside method for assessment of a leak around the ETT cuff by continuous monitoring of Pco 2 at the upper airways. Initially, the feasibility of the method was investigated in a human simulator. Later, leaks at various cuff pressures were evaluated by iodine leak test in a porcine model simulating human airway mucosa. Finally, the feasibility of the method was evaluated in 60 patients undergoing elective surgery, comparing the new method to the standard clinical evaluation used today. Methods To find the best feasible place for CO2 measurements, we evaluated 3 anatomic locations: 1. between the ETT cuff and the vocal cords through a suction mini-guide lumen catheter attached externally to the ETT, 2. at the oropharynx above the epiglottis by a catheter inserted through a plastic oropharyngeal airway, and 3. in the nares of the nose through a nasal cannula Figure 1. The anatomic locations of CO2 sampling in the human simulator and in patients under general anesthesia. Measurements of CO2 levels were done at 3 anatomic locations: 1. between the endotracheal tube (ETT) cuff and the vocal cords through a suction mini-guide lumen attached externally to the ETT, 2. at the oropharynx above the epiglottis by a catheter inserted into a plastic airway, and 3. at the nares of the nose through a nasal cannula. The study was performed in three phases. Phase 1 ascertained feasibility of the method in a human simulator. Phase 2 experimentally explored the method in a porcine model. Phase 3 compared this new method with the standard technique for estimating optimal ETT cuff filling in 60 surgical patients under general anesthesia. Throughout all 3 phases of the study, Pco2 levels were recorded using a micro-side-stream capnograph (Microcap®; Oridion, Jerusalem, Israel) with flow rate of 50 mL/min–7.5 + 15 mL/min and rise time to CO2 step of approximately 0.2 s. By its routine use, the Microcap® uses an algorithm which detects and saves only the end-tidal Pco2 values. To avoid inaccurate processing of Pco2 data by the capnograph, the routinely used algorithm to detect end-tidal Pco2 was neutralized and all Pco2 values were directly transported and saved on a PC computer. We interpreted any increase of >1 mm Hg in Pco2 reading as a sign of leak around the cuff and accordingly set the appropriate cuff pressure. This cuff pressure was automatically kept constant by a special electronic cuff pressure controller device (TRACOE® cuff pressure controller, Germany) with a controlled accuracy of ±2 mbar, avoiding possible cuff pressure changes caused by fluctuations in inspiratory pressures or any other local variables. Throughout the experiment, we used ETTs with high-volume, low-pressure cuffs with an external side-attached mini-guide lumen which opens 1 cm above the cuff (Hi-Lo® Evac, Mallinckrodt). The proximal end of the suction mini-guide was connected to the capnograph (Fig. 1). Figure 2 shows a photograph of the PC display including a graph of the ETT cuff pressure controller and a graph of Pco2 readings in the upper airways of the human simulator. Figure 2. Exhaled CO2 pressure waveform in accordance with endotracheal tube cuff pressures as displayed on the PC monitor in the human simulator model. Suction time (from the upper airways) is represented by the straight line of the CO2 pressure waveform. Phase 1: Human Simulator Model We used a human simulator of a 70-kg man (Medical Education Technologies, Inc. [METI], Sarasota, FL) located in the Israel Sheba Simulation Center. A Hi-Lo® Evac ETT no. 8 was inserted into the human simulator trachea. The tracheal diameter at the location of the ETT cuff was 25 mm. Exhaled air end-tidal CO2 of 40 mm Hg was simulated by adjusting a continuous CO2 stream into the simulator lungs. While ventilating the human simulator, we sequentially inflated the cuff, 2 mm Hg at a time and measured Pco2 leak level at the 3 anatomic sites (Fig. 1). After each cuff pressure change, we suctioned the oropharynx to prevent CO2 remnants from altering subsequent measurements. Phase 2: Porcine Model Experiments were conducted with permission from and according to the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals. Two pigs, weight 10 and 13 kg, underwent general anesthesia with a no.7 ETT. CO2 leak was assessed by a 4-mm-diameter catheter inserted directly through a small incision into the trachea 1 cm above the ETT cuff and below the vocal cords. The ETT cuff pressure was increased sequentially, 2 mm Hg at a time and Pco2 was measured through the catheter. After each measurement, we suctioned the upper airway to avoid any CO2 remnants. After reaching a steady cuff pressure that gave no Pco2 readings at the upper airway, we surgically opened a tracheal “window” below the ETT cuff. Iodine solution (5 mL) was injected above the cuff and rested there for 60 min while we evaluated through the tracheal window any iodine leak below the cuff at different cuff pressure levels. Throughout the experiment (including the period of iodine leak measurements), animals were maintained on the same positive pressure ventilation and the ETT location and animal head and neck positions were not changed. Phase 3: Human Subjects Sixty consecutive adult patients undergoing elective surgery with balanced generalized anesthesia (NO2/O2) were included in our study. To obtain a homogenous group of patients regarding mechanical ventilation volumes and pressures, patients with a history of cigarette smoking or dyspnea were preassessed by pulmonary function tests. Nine patients were excluded because of forced expiratory volume per second (FEV1) or vital capacity (VC) <50% of predicted. The study protocol was approved by the local ethics committee and patients signed an informed consent. In all patients, the tracheal intubation was performed by an anesthesiologist and the ETT position inside the trachea was determined according to the height of the patient, using the following formula: the length from the distal tip of the ETT to the right mouth angle (cm) = [body height (cm)/5] – 13 (16). After intubation, the anesthesiologist was requested to set the minimal ETT cuff pressure required to prevent leak according to exhalation-inhalation volume difference and air leak heard with the stethoscope around the cuff. The cuff pressure was considered optimal by the anesthesiologist when there was no exhalation-inhalation volume difference and no air leak heard with the stethoscope using the minimal cuff pressure for 5 min. Once cuff pressure level was considered optimal by the anesthesiologist, we started measuring Pco2 at the 3 locations: proximal to the ETT cuff via the external mini-guide lumen of the Hi-Lo® Evac ETT, at the oropharynx via a plastic oropharyngeal airway, and at the nares via a nasal cannula (Fig. 1). Based on the findings in the porcine model, optimal cuff filling was defined as the minimal cuff pressure required to avoid a Pco2 leak of >2 mm Hg proximal to the ETT cuff via the external mini-guide lumen of the Hi-Lo® Evac ETT. Suction was performed through the plastic airway as needed and 2 min before each Pco2 measurement. Continuous monitoring of Pco2 from the 3 anatomic locations was performed throughout the operation. Statistical Analysis The statistical SPSS software (version 10.0; SPSS Inc., Chicago, IL) was used for all analyses performed. Categorical data were expressed in numbers and percentages. Continuous data were expressed as means ± standard deviations and compared by a paired t-test. Regression coefficient ® was calculated as a measurement of correlation between ETT cuff pressure and Pco2 in the upper airways and expressed as R2. P values < 0.05 were considered significant. Results Phase 1: Human Simulator Model Figure 2 illustrates an example of the exhaled Pco2 waveform in accordance with ETT cuff pressure as displayed on the PC monitor in the human simulator model. A linear correlation was observed between the ETT cuff pressure and the Pco2 measured above the cuff in all 3 anatomic locations: 1. between the cuff and the vocal cords, R2 = 0.954, P < 0.0001; 2. at the oropharynx above the epiglottis, R2 = 0.923, P < 0.0001; 3. at the nares of the nose, R2 = 0.911, P < 0.0001. Figure 3 demonstrates the correlation between ETT cuff pressures and CO2 levels measured between the cuff and the vocal cords. At an ETT cuff pressure of >>26 mm Hg, no Pco2 was recorded at any of the 3 anatomic locations (Fig. 1). At an ETT cuff pressure of 25 mm Hg, Pco2 was detected only between the cuff and the vocal cords. Once ETT cuff pressure reached 24 mm Hg, CO2 leak was measured at all locations. At all levels of cuff pressures, the maximal difference in Pco2 readings between the various anatomic locations was <2 mm Hg. Figure 3. Correlation between endotracheal tube cuff pressures and CO2 levels, measured between the cuff and the vocal cords, in the human simulator. Phase 2: Porcine Model In animal “A,” the minimal cuff pressure needed to prevent CO2 leak around the ETT cuff was 28 mm Hg whereas the minimal cuff pressure needed to prevent iodine solution leak around the cuff was 24 mm Hg, a pressure at which we already measured a Pco2 leak of 2–3 mm Hg. There was a linear correlation between ETT cuff pressure and Pco2 leak above the cuff (R2 = 0.984, P < 0.0001) Figure 4. Correlation between endotracheal tube cuff pressure and upper airway CO2 levels in the porcine model. The black arrow marks the point at which iodine solution leak was first detected. a, Pig A. b, Pig B. In animal “B,” the minimal cuff pressure needed to prevent CO2 leak around the ETT cuff was 30 mm Hg whereas the minimal cuff pressure needed to prevent iodine solution leak around the cuff was 25 mm Hg, a pressure at which we measured a Pco2 leak of 3–4 mm Hg. There was a linear correlation between the ETT cuff pressure and Pco2 leak above the cuff (R2 = 0.988, P < 0.0001) (Fig. 4b). Phase 3: Human Subjects Baseline characteristics of the patients are summarized in Table 1. The mean age of the patients was 58.5 ± 16.2 yr. The mean peak inspiratory pressure was 21.2 ± 0.6 mm Hg. Although patients with severe pulmonary diseases were excluded from the study (FEV1 or VC <50% of predicted), 6 patients (10%) had mild obstructive lung disease and 1 patient had mild restrictive lung disease. Table 1. Baseline Patient Characteristics The results from the human simulator and the porcine model demonstrated a linear correlation between Pco2 leak measurements and ETT cuff pressures. The fact that iodine solution leak occurred only when the Pco2 leak readings were >2 mm Hg induced us to consider a Pco2 leak measurement clinically significant only if it was >2 mm Hg proximal to the ETT cuff via the external mini-guide lumen of the Hi-Lo® Evac ETT. The mean initial ETT cuff pressure of all of the study population, determined clinically by the anesthesiologist, was significantly higher than the mean optimal cuff pressure determined by upper airway Pco2 leak monitoring proximal to the ETT cuff (25.2 ± 3.6 versus 18.2 ± 7.8 mm Hg, respectively; P < 0.001) (Fig. 5). In 43 patients (72%), the clinically determined ETT cuff pressure was significantly higher than the optimal cuff pressure determined by CO2 leak, with a mean change of 10.2 mm Hg in cuff pressure (25.4 ± 3.9 versus 15.2 ± 4.7 mm Hg, P < 0.0001) (Fig. 6). In 8 patients (13%) the initial ETT cuff pressures were significantly lower than the optimal cuff pressure. Nine patients (15%) had an initial ETT cuff pressure similar to the optimal cuff pressure (Fig. 6). Figure 5. Comparison between the initial mean endotracheal tube cuff pressure, determined clinically by the anesthesiologist using the audible leak test and exhalation-inhalation volume difference, to the mean optimal cuff pressure determined by CO2 leak monitoring (n = 60). Figure 6. Percentage of patients with initial endotracheal tube cuff pressure significantly higher, lower, or accurate compared with the optimal cuff pressure determined by Pco2 leak monitoring (n = 60). In 3 patients, CO2 leak continued despite the exceptionally high cuff pressure, up to 35 mm Hg. The pressures determined by the anesthesiologist in these patients were 30, 32, and 33 mm Hg. After distal repositioning of the ETT, the cuff pressures needed to prevent CO2 leak were reduced to <30 mm Hg, similar to the remainder of the study population. Because cuff pressures required for complete sealing were reduced dramatically after distal reposition, we assumed that the primary incomplete sealing was probably the result of a very high proximal airway position causing poor contact between the ETT cuff and the patient airway anatomy (e.g., direct contact between the cuff and the vocal cords). During surgery, a new leak of CO2 around the ETT cuff developed in 16 patients (27%) attributable to variable causes such as increased peak inspiratory pressure by >5 mm Hg caused by laparoscopic surgery with abdominal gas inflation, light anesthesia or inadequate neuromuscular blockade, change of head position because of surgical requirements, and ETT movement during surgery (Table 2). Table 2. Causes of a New Leak Around the Endotracheal Tube Cuff During Operation During surgery, CO2 recordings were obtained at all 3 anatomic locations (Fig. 1) and differences in Pco2 readings were <2 mm Hg. After a mean of 9 ± 4 measurements through the suction mini-guide catheter attached to the ETT, no further readings could be obtained because of obstruction by secretions and thus further Pco2 readings were obtained only from the plastic airway (hypopharynx) and from the nares. Discussion Methods used today to determine adequate cuff filling are either inaccurate or cumbersome (13,14). An underfilled cuff may cause aspiration of nasopharyngeal content whereas an overfilled cuff may cause local mechanical injury (1–9). The ETT bypasses normal upper airway reflexes preventing effective cough, thus facilitating pooling of nasopharyngeal secretions above the cuff which tend to “trickle” down the airway and cause VAP. Kollef et al. (17) have shown that, in patients undergoing cardiac surgery with mechanical ventilation, reducing aspiration around the ETT cuff by continuous suctioning proximal to the cuff delayed the occurrence of VAP from 2.9 ± 1.2 to 5.6 ± 2.3 days (P = 0.006). The independent risk of the ETT in ventilated patients may be deduced from studies of noninvasive ventilations (NIV). In a matched case-control study, Girou et al. (18) found that, among ICU patients, NIV reduced nosocomial pneumonia from 60% to 18% (P < 0.001). Similarly, in a large survey, 42 ICU patients receiving NIV were less likely to develop pneumonia, even after adjustment for severity of illness (19). The findings of these studies support the assumption that prevention of aspiration around the ETT cuff is crucial in order to avoid VAP. In this study, we evaluated a new, objective, noninvasive method for determining the appropriate ETT cuff filling by continuous Pco2 monitoring at the upper airway. The method was first evaluated objectively on a human simulator model with well established anatomic structures and an unbiased environment with no secretions or nonconstant variables. The linear correlation we found between the ETT cuff pressure and CO2 leak above the cuff shows that Pco2 can be used as a quantitative indicator of air leak (Fig. 3). Although there was an overall linear correlation between ETT cuff pressure and Pco2 in the upper airways (R2 > 0.91, P < 0.0001 for all 3 anatomic locations), the correlation seems less linear at the beginning and at the end of the curve, with lower Pco2 changes than expected compared with the increase in cuff pressure (Fig. 3). This could be because, at very low cuff pressures, there is still considerable space which allows for continuous CO2 leaks, whereas, at high cuff pressures, with minimal CO2 leakage, there is a need for higher changes in cuff pressures to achieve complete sealing of the trachea by the cuff. The human simulator represents the human airway anatomy but it cannot imitate the interactions between the natural human mucosa and the ETT cuff. Therefore, in phase 2, a porcine model was used to assess iodine leak around the cuff. Because iodine is less viscous than pharyngeal secretions, we assumed that the cuff pressure needed to prevent iodine leak would be sufficient to prevent secretion leak around the ETT cuff. In this model, using sequential increases of 2 mm Hg in cuff pressure, iodine leak around the cuff occurred only when Pco2 readings were >2 mm Hg, suggesting that the Pco2 leak test has a safety margin of 2 mm Hg. Based on these findings, and considering that maximal change in Pco2 measurements among the 3 above-cuff anatomic locations was <2 mm Hg, we concluded that clinical practice measurements of Pco2 at the oropharynx or the nares of the nose are equivalent to distal measurements just above cuff, which we found technically difficult. This second phase of the study was conducted in only two pigs because of limitations and restrictions by the National Institutes of Health Guidelines for the Care and Use of Laboratory Animals. Differences between the cuff pressure needed to prevent CO2 leak and that needed to prevent iodine leak in both pigs were almost identical, so it seemed inappropriate to kill more animals for this model. In the third phase of the study, we evaluated the method in patients undergoing elective surgery under general anesthesia. The mean initial ETT cuff pressure determined clinically by the anesthesiologist was significantly higher than the optimal cuff pressure assessed by CO2 leak monitoring (in all patients, 25.2 ± 3.6 versus 18.2 ± 7.8 mm Hg, P < 0.001) (Figs. 5 and 6). In 72% of the patients, primary ETT cuff pressures were significantly higher than the optimal cuff pressure determined by Pco2 readings, with a mean change of 10.2 mm Hg. An over-inflated cuff increases the risk of mucosal ulcerations, granulomas, tracheal stenosis, and tracheoesophageal fistulae (1–4). The consequences of these complications are of significant clinical importance because surgical corrections are not always successful (1–4). The mechanisms are related to direct pressure necrosis by over-inflated ETT cuff duration of intubation, macro- and microtrauma during intubation, the specific technique of endotracheal intubation, severity of respiratory failure, infection, and poor tissue perfusion caused by hemodynamic instability (1–4,20). These mechanical complications are less common in elective surgical patients, and are seen mostly in patients with prolonged mechanical ventilation, such as ICU patients (1,2,4,20). The proposed Pco2 method helps determine the minimal initial cuff pressure needed to prevent a leak. However, after the initial setting, another regulatory problem, not yet solved, is the need to deflate the cuff in order to evaluate the possibility of pressure reduction (required, for example, after decreasing respiratory pressures) and then inflate it again according to the new CO2 readings. A further study is needed to evaluate the regulatory of an over-inflated cuff. Although the general tendency of the anesthesiologists was to “overshoot” the initial cuff pressure, we found, in 13% of the cases, lower than optimal initial cuff pressures. Moreover, during surgery, a new leak developed in 27% of the patients, potentially exposing them to aspiration risk. This variability in cuff pressure, observed even in stable elective surgery patients, emphasizes the need for an accurate, continuous bedside method to determine the appropriate cuff pressure. An important problem encountered during the study was obstruction by secretions of the mini-guide lumen of the Hi-Lo® Evac ETT after several aspirations for Pco2 measurements, despite suctioning of the upper airways. In contrast, Pco2 readings through nasal cannula, or from the oropharynx through the plastic airway, were easily obtained after secretion clearance by oral suctioning. The obstruction of the mini-guide catheter lumen, with its tip located in the trachea, by secretions, prevents its use for monitoring CO2 leak. But because the maximal difference in Pco2 readings between the 3 anatomic locations was <2 mm Hg (a pressure not causing iodine leak), we suggest the nares of the nose or the oropharynx as the locations of choice for CO2 sampling. However, we must emphasize that these findings are based on a one-size human simulator model and only 60 adult anesthetized patients. It is possible that, in patients with diverse anatomic variations, differences in Pco2 reading between the trachea and the oropharynx or the nares will be >2 mm Hg. Further study is needed to evaluate the optimal place for CO2 sampling in a larger study population with a variety of airway anatomies. Another important issue is the position of the ETT. A malpositioned ETT is hazardous for tracheally intubated patients. Insertion of an ETT too distally leads to endobronchial intubation, which may cause collapse of the contralateral lung, whereas proximal insertion may lead to accidental extubation or vocal cord trauma (20,21). Several formulae and other methods have been proposed to estimate the optimal length for ETT insertion; however, none is always satisfactory (22–25). In the current study, 3 patients had a CO2 leak despite exceptionally high (>35 mm Hg) cuff pressures. However, pressure decreased to <30 mm Hg (as in the remainder of the study population) after distal repositioning of the ETT. Although it was not the aim of the study, continuous CO2 leak around an appropriately inflated cuff can be used as a marker for malpositioned ETT. Incessant CO2 leak around the ETT cuff can occur when there is incomplete sealing caused by poor contact with the vocal cords, endobronchial intubation (CO2 from the contralateral lung), or intubation above the vocal cords. Regarding comparisons between the above cuff CO2 measurement and the audible leak test, several differences should be noted. Although both methods evaluate air leak around the ETT cuff, the CO2 method is an objective, accurate technique that could be automated and used as a standard in clinical trials and later as a standard of care for intubated patients, aiming to reduce complications related to the ETT tube. However, the CO2 method has several important limitations: 1. the technique requires adequate equipment, including a second capnograph (besides the capnograph used for measurements of intra-ETT CO2) and a cuff pressure controller device; 2. the need for oropharynx suctioning between samples of CO2 measurements at different cuff pressures is cumbersome and prolongs the time needed to achieve optimal cuff filling. We hope that we will soon be able to supply an automatic device capable of synchronizing the CO2 measurements, the cuff pressure controller, and the suction. The study has several limitations: 1. the study did not include ICU patients who required prolonged mechanical ventilation. 2. The experiment was performed only during positive pressure ventilation whereas the CO2 method may not be as reliable in spontaneously breathing patients. 3. Patients with moderate-to-severe pulmonary disease were not included in the study. However, there is a real need for a simple, noninvasive method that can be used as an objective standard in clinical practice and in studies addressing the important issue of leak around the cuff. This standard may be applied not only to short-term over-inflation of ETT cuffs in the operating room, which has less significant clinical importance, but also to more complicated conditions, such as in neonates, children, patients with pulmonary diseases or anatomic malformations, and ICU patients. However, before using this new method in more complicated conditions, we evaluated the method in optimal conditions. In this study, we evaluated a new, objective method for optimizing ETT cuff filling by monitoring CO2 levels in the upper airways. The method is simple, noninvasive, and can be used in any tracheally intubated patient. Continuous CO2 monitoring in the upper airway can be used to identify the minimal cuff pressure needed to prevent an air leak around the ETT cuff. Data obtained in two pigs suggest that this method may also be useful for identifying the cuff pressure that would prevent aspiration of secretions around the cuff. Before the CO2-based cuff inflation method can be use as a standard of care for all tracheally intubated patients, further studies comparing the clinical relevance of the differences between the audible leak test to the CO2 method are needed for patients more prone to ETT complications, such as those with pulmonary diseases, ICU patients, and children. References 1.Stauffer JL, Olson DE, Petty TL. Complications and consequences of endotracheal intubation and tracheotomy: a prospective study of 150 critically ill adult patients. Am J Med 1981;70:65–76. SFX Bibliographic Links Library Holdings [Context Link] 2.Lewis FR Jr, Schiobohm RM, Thomas AN. Prevention of complications from prolonged tracheal intubation. Am J Surg 1978;135:452–7. 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SFX Library Holdings [Context Link] 8.Spray SB, Zuidema GD, Cameron JL. Aspiration pneumonia: incidence of aspiration with endotracheal tubes. Am J Surg 1976;131:701–3. [Context Link] 9.Craven DE, Steger KA. Epidemiology of nosocomial pneumonia: new perspectives on an old disease. Chest 1995;108:1–16. [Context Link] 10.Kearl RA, Hooper RG. Massive airway leaks: an analysis of the role of endotracheal tubes. Crit Care Med 1993;21:518–21. SFX Bibliographic Links Library Holdings [Context Link] 11.Guyton DC, Barlow MR, Besselievre TR. Influence of airway pressure on minimum occlusive endotracheal tube cuff pressure. Crit Care Med 1997;25:91–4. Ovid Full Text Bibliographic Links Library Holdings [Context Link] 12.Fisher MM, Raper RF. The “cuff-leak” test for extubation. Anaesthesia 1992;47:10–2. SFX Bibliographic Links Library Holdings [Context Link] 13.Petring OU, Adelhoj B, Jensen BN, et al. Prevention of silent aspiration due to leaks around cuffs of endotracheal tubes. Anesth Analg 1986;65:777–80. SFX Bibliographic Links Library Holdings [Context Link] 14.Young PJ, Basson C, Hamilton D, Ridley SA. Prevention of tracheal aspiration using the pressure-limited tracheal tube cuff. Anaesthesia 1999;54:559–63. SFX Bibliographic Links Library Holdings [Context Link] 15.Schmitz BD, Shapiro BA. Capnography. Respir Care Clin North Am 1995;1:107–17. [Context Link] 16.Cherng CH, Wong CS, Hsu CH, Ho ST. Airway length in adults: estimation of the optimal endotracheal tube length for orotracheal intubation. J Clin Anesth 2002;14:271–4. SFX Bibliographic Links Library Holdings [Context Link] 17.Kollef MH, Skubas NJ, Sundt TM. A randomized clinical trial of continuous aspiration of subglottic secretions in cardiac surgery patients. Chest 1999;116:1339–46. Ovid Full Text Bibliographic Links Library Holdings [Context Link] 18.Girou E, Schortgen F, Delclaux C, et al. Association of noninvasive ventilation with nosocomial infections and survival in critically ill patients. JAMA 2000;284:2361–7. Ovid Full Text Bibliographic Links Library Holdings [Context Link] 19.Carlucci A, Richard JC, Wysocki M, et al. Noninvasive versus conventional mechanical ventilation: an epidemiologic survey. Am J Respir Crit Care Med 2001;163:874–80. SFX Bibliographic Links Library Holdings [Context Link] 20.Streitz JM Jr, Shapshay SM. Airway injury after tracheotomy and endotracheal intubation. Surg Clin North Am 1991;71:1211–30. SFX Bibliographic Links Library Holdings [Context Link] 21.Cavo JW Jr. True vocal cord paralysis following intubation. Laryngoscope 1985;95:1352–9. SFX Bibliographic Links Library Holdings [Context Link] 22.Owen RL, Cheney FW. Endobronchial intubation: a preventable complication. Anesthesiology 1987;67:255–7. SFX Bibliographic Links Library Holdings [Context Link] 23.Mehta S. Intubation guide marks for correct tube placement: a clinical study. Anaesthesia 199;46:306–8. [Context Link] 24.Patel N, Mahajan RP, Ellis FR. Estimation of the correct length of tracheal tubes in adults. Anaesthesia 1993;48:74–5. SFX Bibliographic Links Library Holdings [Context Link] 25.Cherng CH, Wong CS, Hsu CH, Ho ST. Airway length in adults: estimation of the optimal endotracheal tube length for orotracheal intubation. J Clin Anesth 2002;14:271–4. SFX Bibliographic Links Library Holdings [Context Link] Is Capnometry the Optimum Method for Assessing the Adequacy of Endotracheal Tube Cuff Seal? [Letters to the Editor] Sosis, Mitchel B. MS, MD, PhD Board Certified Anesthesiologist, Lafayette Hill, PA, mitchelsosis@hotmail.com To the Editor: Efrati et al. (1) recently proposed a new technique for assessing the adequacy of endotracheal tube cuff seal on the basis of upper airway capnometry at three sites. The cuffs were inflated until a leak of <=2 mm Hg of carbon dioxide was detected. This was compared to the “standard” technique of filling the cuffs by listening for a leak and by comparing inspired and expired tidal volumes. They concluded that capnographic sampling of carbon dioxide via a nasal cannula could “objectively” detect an inadequately inflated endotracheal tube cuff in a patient undergoing general orotracheal anesthesia. Carbon dioxide is not always detected via a nasal cannula in spontaneously breathing non-intubated patients. The reason, of course, is that the patient can choose to breathe through the mouth. Unless the mouth is somehow sealed in intubated patients, it seems that there is no guarantee that a nasal cannula would detect carbon dioxide leaking past the endotracheal tube cuff. In the clinical limb of this study, Efrati et al. compared the proposed capnometric technique to the standard technique. The authors noted a slightly lower mean cuff pressure (25.2 ± 3.6 versus 18.2 ± 7.8) with capnography. However, it is not clear whether clinicians were blinded as to cuff pressures, and/or attempted to minimize those pressures, when using the standard technique. The authors did not assess postoperative sore throat, aspiration, or other sequelae of endotracheal intubation. Consequently, no clinical benefit of the capnometric technique was demonstrated. Mitchel B. Sosis, MS, MD, PhD Board Certified Anesthesiologist Lafayette Hill, PA mitchelsosis@hotmail.com Reference 1. Efrati S, Leonov Y, Oron A, et al. Optimization of endotracheal tube cuff filling by continuous upper airway carbon dioxide monitoring. Anesth Analg 2005; 101:1081–8. Ovid Full Text Bibliographic Links Library Holdings [Context Link]

Fo those who are interested in reading more about this there is a thread here:: Saved! New Paramedic Drama on TNT

Hello Everyone, Here's a great PPT lecture on: End Points of Resuscitation:When have I done enough? http://www.gasnet.org/lectures/calkins.res...files/frame.htm Enjoy, ACE844

"FL_Medic," Here's a link to a 'paramedic RSI' protocol -rationale document where there are examples of this. http://www.azdhs.gov/diro/admin_rules/guid...067-phs-ems.pdf Out here, ACE844

This Thread is :::

"AZCEP," As usual you hit the proverbial 'nail on the head'. That was exactly my point.[/font:1fa58b239c] "FL_Medic," I am not arguing, my point was to cause you to do some research where you would most certainly find that IN FACT BENZODIAZEPINES ARE NOT NARCOTICS...They are sedatives. As far as your hospitals comment. Perhaps that is just in your area. In the NorthEast I spend ALOT of time in the hospital and in my experience here have yet to run into a single doc, anestheasiologist, etc... who doesn't know or understand the difference. Here is a great book to help you with this subject and understand why this is important.[/font:1fa58b239c] Other sources and information can be found here by doing a search for ETI, RSI, andd individually for the various meds which make up the part of your sequence. Here's one to get you started: [/font:1fa58b239c] Teaching Points:::: Intubation-RSI I think what you'll find here is part of what makes this site different from other EMS 'forums' is we expect a higher standard, and try to do our best to educate each other and learn as much as possible about EMS and medicine. Also, unofficially we have a sort of policy here where if one makes clinical or medicine related statements and purports it as fact; that we usually ask for independently cerifiable studies and literature which support your 'claims'. Like I said in my original post, based on your posts which I've read you seems to be a smart guy who wants to advance himself and EMS, thats why I asked for supporting information where if you had info. which no of us had perhaps we could all learn from it. Out Here, ACE844[/font:1fa58b239c]

You seem like a smart guy....Kindly back up your claim with evidence, and studies to support your position of Thanks, ACE844

You should be giving your patients narcotics-analgesia coverage as part of your sequence...DO YOU??!!

You want the renal effects of the dopa for the reasons mentioned and also for the fact you don't want this patient to develop ATN 2nd to shock, and you don't want a similar set up with the liver...Backing off the dopa completely menas your just using it for a band aid and you'll be re-starting it shortly there after.

I think they have a minimum cognitive ability requirement...Like say the ability to speak and spell above the 2nd grade, yeah...Maybe when you make it all the way to 10th grade level.. :roll: they may have something for ya!

What do you use for analgesia as part of your induction and ongoing paralysis s/p RSI?

There were other issues....WHERE??? I'M shocked to learn this! :shock:

With all due respect and presesnted for your consideration, I think you should consider the following: This took place in South Africa, one of the few places on the planet where they have a doctorate program for EMS... ACE