Teaching Points:::: Intubation-RSI

[Ace844]

Hello Everyone,

Since we discuss this alot here I thought that perhaps I would make this teaching post and allow some of you all to benefit alittle from the wisdom of Ron Walls MD, whose bokk is highly recommened here by ALL OF US WHO HAVE IT, and it is in the EMTCITY Book Club. If for whatever reason you can't get it, or are to lazy to, here's just a small taste of what you've been missing. LIKE IT, LOVE IT, KNOW IT READ IT, MEMORIZE IT, READ IT AGAIN!!!!

Enjoy,

ACE844

Ron M. Walls

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PERSPECTIVE

Airway management is a defining element for the specialty of emergency medicine. Although practitioners from other specialties often have knowledge and skills that overlap those of the emergency physician (EP), the ability to provide critical care and definitive airway management for all patients, regardless of the cause of their presentation, is unique to the specialty of emergency medicine. The EP has primary responsibility for management of the airway, which cannot be abrogated to another specialty. All techniques of airway management lie within the domain of emergency medicine. Rapid sequence intubation (RSI) is the cornerstone, but emergency airway management includes various intubation maneuvers, use of ancillary devices, approaches to the difficult airway, and rescue techniques when intubation fails.

Since the first reported use of neuromuscular blocking agents (NMBAs) in the emergency department (ED) by emergency personnel in 1971, there has been progressive sophistication of emergency airway techniques, pharmacologic agents, and special devices used to facilitate intubation.[1] [2] The American College of Emergency Physicians (ACEP) articulated in its policy statement on RSI that the use of NMBAs to facilitate tracheal intubation is within the domain of emergency medicine and that EPs should possess the necessary knowledge, experience, and training to apply RSI in the clinical care of their patients.

PATHOPHYSIOLOGY

The Decision to Intubate

Critical care courses such as Advanced Trauma Life Support (ATLS) and Advanced Cardiac Life Support (ACLS) address the technique of intubation but give little consideration to when or how to intubate. Although intubation presents a technical challenge to the physician, often a greater challenge lies in deciding the optimum timing, route, and method of intubation. The flaccid, unconscious, unresponsive patient clearly needs immediate, definitive airway intervention. The young patient with mild asthma responding to inhaled therapy clearly does not need intubation. Between these two extremes, clinical presentations vary from mild airway compromise to impending death. The challenge is in deciding which of these patients requires intubation, a decision that must often be reached long before the patient is in obvious clinical crisis.

A decision to intubate should be based on three essential criteria: (1) failure to maintain or protect the airway, (2) failure of ventilation or oxygenation, and (3) anticipated need for intubation based on the patient's clinical course and likelihood of deterioration.

Failure to Maintain or Protect the Airway

A patent airway is essential for adequate ventilation and oxygenation. If the patient is unable to maintain the airway, patency must be established by artificial means, such as repositioning, chin lift, jaw thrust, or insertion of an oral or nasal airway. Likewise, the patient must be able to protect against aspiration of gastric contents, which carries significant morbidity and mortality. Traditionally, presence or absence of a gag reflex has been advocated as a reliable indicator of the patient's ability to protect the airway, but this has not been subjected to proper scientific study and probably has little relevance to airway protection. A more reliable indicator may be the patient's ability to swallow or handle secretions, but this also remains to be tested. In general, a patient who requires a maneuver to establish a patent airway will probably require intubation for protection of that airway unless a readily reversible condition, such as opioid overdose, is present.

Failure of Ventilation or Oxygenation

Ventilatory failure that is not reversible by clinical means or increasing hypoxemia that is not adequately responsive to supplemental oxygen is a primary indication for intubation. This assessment is clinical and includes evaluation of the patient's general status, oxygenation by pulse oximetry, and anticipated clinical course. Arterial blood gases (ABGs) are generally not required to make a determination regarding the patient's need for intubation. In most circumstances, clinical assessment, including pulse oximetry, and observation of improvement or deterioration will lead to a correct decision. ABGs may be helpful in some circumstances but also may be misleading, so they must be interpreted in the context of the patient's clinical status. Patients who are clinically stable or improving despite severe ABG alterations may not require intubation, whereas a rapidly tiring asthmatic patient may require intubation when ABG values are only modestly disturbed, or even improving.

Regardless of the underlying cause, the need for mechanical ventilation generally mandates intubation. External mask devices have been increasingly used to provide assisted mechanical ventilation without intubation[4] (see Chapter 2 ), but despite these advances, most patients who need assisted ventilation or positive pressure to improve oxygenation require intubation.

Anticipated Need for Intubation

Certain conditions indicate the need for intubation even in the absence of airway, ventilatory, or oxygenation failure. Status epilepticus, severe multiple trauma, certain overdoses, and penetrating neck trauma are conditions that require intubation before the airway or gas exchange is compromised. For example, intubation may be indicated relatively early in the course of severe cyclic antidepressant overdose. Although the patient is awake, protecting the airway and exchanging gas well, intubation is advisable to guard against the strong likelihood of clinical deterioration, including coma, seizure, and possible aspiration of activated charcoal, which can occur over a short time.

Significant multiple trauma, with or without head injury, may be an indication for intubation.[5] Many of these patients

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are ventilating normally through a patent airway, and oxygen levels are frequently normal or supernormal with supplemental oxygen. Despite this, anticipated deterioration, loss of the ability to protect the airway, and the need for studies outside the ED (e.g., multiple radiographs, angiography) may mandate intubation. The patient with penetrating neck trauma may present with a patent airway and adequate gas exchange. Nevertheless, intubation is advisable with any evidence of vascular or airway injury because these patients tend to deteriorate and because increasing hemorrhage or swelling in the neck tends to compromise the airway and confound later attempts at intubation.[6]

Although these indications for intubation may seem quite different and individualized, the common thread is the anticipated clinical course over time. In each circumstance it can be anticipated that future events will compromise either the patient's ability to maintain and protect the airway or the patient's ability to oxygenate and ventilate. Therefore knowledge of the natural history of the emergency condition is essential to determine whether intubation is necessary when airway compromise or gas exchange failure is not present on evaluation. A similar thought process is applied to any patient who will be leaving the ED for diagnostic studies such as a computed tomography (CT) scan or who may be transported to another facility. If it seems clinically likely that the patient may deteriorate, “prophylactic” intubation is the prudent course.

CLINICAL FEATURES

Identification of the Difficult Airway

In most patients, even in the ED's precipitous and unpredictable environment, the intubation is technically easy and straightforward. Intubation failure occurs in approximately 1:100 elective general anesthesia cases; intubation failure combined with failure of bag/mask ventilation (BMV) is exceedingly rare, between 1:5000 and 1:200,000 patients.[7] [8] These numbers cannot be applied directly to the ED situation but are reassuring in that they indicate a high degree of safety if a preintubation analysis of factors predicting difficult intubation is undertaken. Large ED intubation series, including one series of more than 4800 intubations from 26 departments, demonstrate failure rates for RSI in ED patients of approximately 1% to 2%.[1] [9]

In certain patients the physician can predict that intubation will be difficult. Evaluation of all patients for markers of difficult intubation allows the physician to plan an appropriate approach to the airway. The emergency nature of the patient's presentation often precludes postponement of the intubation, even for a short time, but knowledge of the difficulties presented by the patient's airway permits thoughtful planning and preparation for possible intubation failure. Neuromuscular paralysis should be avoided in patients for whom a high degree of intubation difficulty is predicted, unless the administration of NMBAs is part of a planned approach to the difficult airway. This approach is described later and may include use of a double setup, in which an alternative approach, such as cricothyrotomy, is simultaneously prepared.

Preintubation evaluation should be as comprehensive as clinical circumstances permit. A systematic approach to the patient is required. Unfortunately, most of the difficult airway markers discussed in the anesthesia and emergency medicine literature have not been scientifically validated. Nevertheless, a methodical approach can be used to evaluate the patient,

Box 1-1. External Markers of Difficult Intubation and Difficult Bag/Mask Ventilation (BMV)

Difficult Intubation

Anatomically abnormal facies

Neck trauma

Prominent incisors

Receding mandible

Cervical spine immobilization

Short, thick neck

Difficult Bag/Mask Ventilation

Edentulousness

Obesity

History of snoring

Beard

Age > 55 years

Anatomically abnormal facies

Facial/neck trauma

Obstructive airways disease

Third-trimester pregnancy

Difficult Intubation and Difficult BMV

Anatomically abnormal facies

Facial/neck trauma

Morbid obesity

based on the accepted markers of difficult intubation. The patient first should be inspected for external markers of difficult intubation or difficult BMV ( Box 1–1 ).[10]

The second step in the evaluation of the difficult airway is to assess the patient's anatomy with respect to its suitability for direct laryngoscopy. Direct laryngoscopy requires alignment of the oral, pharyngeal, and laryngeal axes. Success in achieving this alignment requires adequate neck mobility, mouth opening, oral access, and relative size and distance proportions. Neck mobility is assessed by having the patient flex and extend the head and neck through a full range of motion. Modest limitations of motion will not seriously impair laryngoscopy, but severe loss of motion may render laryngoscopy impossible. Cervical spine immobilization in trauma artificially reduces cervical spine mobility and also predicts a more difficult laryngoscopy. Mouth opening is assessed by having the patient open the mouth as wide as possible. Ideally the examiner should be able to insert three of the patient's fingers between the upper and lower incisors. This is typically done by comparing the examiner's fingers to those of the patient, then estimating the width equivalent to three of the patient's fingers.

Oral access is assessed using the Mallampati scale ( Figure 1–1 ). Visibility of the oral pharynx ranges from complete visualization, including the tonsillar pillars (class I), to no visualization at all, with the tongue pressed against the hard palate (class IV). Class I and II predict adequate oral access, class III represents moderate difficulty, and class IV predicts a high degree of difficulty. A recent study challenged the interobserver reliability of the Mallampati score and showed that different, experienced observers agreed only 61% of the time, but that 81% of patients were given the same grade or differed by only one grade

The key geometric relationships for laryngoscopy are the size of the mandible, represented by the distance from the mentum (chin) to the hyoid bone, and the position of the larynx in the neck, represented by the distance from the laryngeal prominence (Adam's apple) to the undersurface of the mandible. Adequate laryngoscopic geometry is present if the first distance is approximately three of the patient's fingerbreadths and the second distance at least two fingerbreadths.[12] Although either significantly increased or decreased distances in these two dimensions can correlate with intubation difficulty, inadequate distance is a much more serious issue. A patient with a receding mandible and high-riding larynx is virtually impossible to intubate using direct laryngoscopy.

The final attribute for difficult intubation is the suspicion or known presence of upper airway obstruction. Conditions such as epiglottitis, laryngeal tumor, neck hematoma, and glottic polyps can compromise laryngoscopy, passage of the endotracheal (ET) tube, BMV, or all three. Physical examination for airway obstruction is combined with assessment of the patient's voice to satisfy this evaluation step ( Box 1–2 ).

Box 1-2. Evaluation of the Difficult Airway

Inspect the patient for external markers of difficult intubation, difficult bag/mask ventilation, or both.

Assess cervical spine mobility.

Assess mouth opening (three fingers between the incisors).

Assess oral access (Mallampati scale).

Assess laryngoscopic geometry (mentum to hyoid, laryngeal prominence to floor of mandible).

Evaluate for obstruction.

Identification of a difficult intubation does not preclude use of a rapid sequence technique. The crucial determination is whether the patient can be ventilated successfully in the event of intubation failure. In general, if intubation is believed to be significantly unlikely and ventilation is judged likely to be unsuccessful, an “awake” technique should be used.[7] [8] The approach to the difficult airway is discussed later.

Measurement of Intubation Difficulty

The actual degree to which an intubation is “difficult” is highly subjective, and quantification is challenging. Research has relied on laryngoscopic view to characterize the intubation difficulty, and the most widely used system is that of Cormack and Lehane,[13] which grades laryngoscopy according to the extent to which laryngeal and glottic structures can be seen. In grade 1 laryngoscopy the entire glottic aperture is seen. Grade 2 laryngoscopy visualizes only a portion of the glottis (arytenoid cartilages alone or arytenoid cartilages plus part of the vocal cords). Grade 3 laryngoscopy occurs when only the epiglottis can be seen. In grade 4 laryngoscopy, even the epiglottis is not visible.

Research conducted on elective anesthesia patients suggests that true grade 4 laryngoscopy, which is associated with impossible intubation, occurs in less than 1% of patients. Grade 3 laryngoscopy, which represents extreme intubation difficulty, is found in less than 5% of patients. Grade 2 laryngoscopy, which occurs in 10% to 30% of patients, can be further subdivided into grade 2a, in which arytenoids and a portion of the vocal cords are seen, and grade 2b, in which only the arytenoids are seen. Intubation failure occurs in 67% of 2b cases but only 4% of 2a cases.[14] Approximately 80% of all grade 2 laryngoscopies are grade 2a, the rest are grade 2b. A grade 1 view is associated with 100% intubation success.

Comparison of difficult intubations between operators and institutions has been difficult. Laryngoscopic view, which is technique dependent and varies among operators, is only one of several determinants of difficult intubation. The intubation difficulty scale (IDS) uses number of operators required, number of devices used, number of attempts, laryngoscopic grade, and other attributes to develop a score for each patient[15] ( Box 1–3 ). A perfect intubation is done by the first operator on the first attempt, using the first selected device, with a grade 1 laryngoscopic view, fully abducted vocal cords, and so on. The IDS shows very high correlation with other measures of intubation difficulty (time, subjective impression). Although developed for anesthesia research, the scale may be applicable to ED intubations as well and might serve as a useful quality measure. Further research is needed

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Box 1-3. The Intubation Difficulty Scale *

Number of intubation attempts > 1

Number of intubators > 1

Number of alternative techniques used

Cormack glottic visualization score (0 = complete, 3 = nonvisualization)

Lifting force for laryngoscopy (0 or 1)

External laryngeal pressure to visualize cords (0 or 1)

Vocal cords abducted? (0 or 1)

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* An ideal intubation would receive a score of zero.

to determine the role of such measurement instruments in emergency airway management.

Confirmation of Endotracheal Tube Placement

Clinical Assessment

The most serious complication of ET intubation is unrecognized esophageal intubation with resultant hypoxic brain injury. Although direct visualization of the ET tube passing through the vocal cords has been considered a reliable indicator of tracheal intubation, such clinical anatomic observations are fallible, and additional means are required to ensure correct placement of the tube within the trachea. Traditional methods, such as chest auscultation, gastric auscultation, bag resistance, exhaled volume, visualization of condensation within the ET tube, and chest radiography, are all prone to failure as means of confirming ET intubation.[16] Fortunately, other clinical techniques are readily available for detecting tracheal or esophageal intubation.

Immediately after intubation, the intubator should auscultate both lung fields and the epigastric area. Auscultation of typical hollow, gurgling, gastric sounds in the epigastrium is highly suggestive of esophageal intubation and should prompt consideration of immediate extubation for reintubation. Pulse oximetry is indicated as a monitoring technique in all critically ill patients, not only those requiring intubation. Oximetry is useful in detecting esophageal intubation but may not show a decreasing oxygen saturation for several minutes after a failed intubation because of the oxygen reservoir created in the patient before intubation. Oximetry may be particularly misleading in the spontaneously breathing patient who has had an inadvertent nasal-esophageal intubation. In this case, oxygen saturation may be preserved because of spontaneous respirations, but catastrophe will ensue if the patient is later paralyzed or heavily sedated in the mistaken belief that the tube is in the trachea.

In addition to oximetry, an independent method of tube placement verification must be used. Two such methods are readily available and highly reliable in the ED setting.

End-tidal Carbon Dioxide Detection

End-tidal carbon dioxide (CO2 ) detection is highly reliable in identification of both tracheal and esophageal intubation in patients with spontaneous circulation.[17] [18] These devices indicate the CO2 content in exhaled air either qualitatively or quantitatively. The persistence of detected CO2 after six manual breaths indicates tracheal intubation. Rarely, BMV before intubation may lead to release of CO2 from the stomach after esophageal intubation, causing a false indication of tracheal intubation. Washout of this phenomenon occurs within six

Figure 1-2 Colorimetric end-tidal CO2 detector. The central disk changes color to match a color scale with indicated concentrations of CO2.

breaths, however, so persistence of CO2 detection after six breaths indicates tracheal intubation.

Although end-tidal CO2 detection is highly sensitive and specific for detecting esophageal intubation, caution is required for patients with cardiopulmonary arrest. Insufficient gas exchange may hamper CO2 detection in the exhaled air, even when the tube is correctly placed within the trachea.[19] Therefore, in patients with cardiopulmonary arrest, a CO2 level greater than 2% should be considered definitive evidence of correct tracheal placement, but the absence of such CO2 cannot be reliably used as an indicator of esophageal intubation. This circumstance arises in approximately 25% of intubated cardiac arrest patients. In all other patients, absence of CO2 detection indicates failure to intubate the trachea, and immediate reintubation is indicated.

It is generally not sufficient to perform laryngoscopy to “confirm” that the tube is through the glottis, since error and misinterpretation can occur; the objective instrument (end-tidal CO2 ) should be considered correct. Similarly, failure of CO2 detection should not be ascribed to other causes, such as severe asthma, in which the physician might postulate that adequate CO2 exchange is not occurring for physiologic reasons. This does not occur, and detection failure should be equated with intubation failure. A positive CO2 reading can also occur when the tube has been misplaced above the glottis or in a mainstem bronchus, where gas exchange can occur despite the lack of tracheal intubation. Other findings, such as tube length, “cuff leak” during ventilation, or ineffective ventilation, generally will identify misplacement.

Disposable, colorimetric end-tidal CO2 detectors are highly reliable, convenient, and easy to interpret, indicating adequate CO2 detection by color change ( Figure 1–2 ) (see Chapter 3 ).

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Aspiration Techniques

The other method of tube placement confirmation is the aspiration technique, which is based on the anatomic differences between the trachea and the esophagus. The esophagus is a muscular structure with no support within its walls. The trachea is held patent by cartilaginous rings. Therefore vigorous aspiration of air through the ET tube with the ET tube cuff deflated results in occlusion of the ET tube orifices by the soft walls of the esophagus, whereas tracheal placement of the tube permits easy and rapid aspiration of air. Such techniques have a sensitivity of nearly 100% for tracheal intubation and sensitivity greater than 90% for detecting esophageal intubation.[20]

Aspiration devices may be useful in the out-of-hospital setting when colorimetric end-tidal CO2 determination is hampered by poor lighting. They are also good backup devices when cardiac arrest confounds attempts to assess placement using end-tidal CO2 .[20] Detection of expired CO2 is more reliable and should be considered the standard for confirmation of tracheal placement of an endotracheal tube and for early detection of accidental esophageal intubation. Aspiration devices have a valuable, secondary role.[21]

Chest Radiography

Although chest radiography is universally recommended after ET tube placement, its primary purpose is to ensure that the tube is well positioned below the cords and above the carina. A single anteroposterior chest radiograph is not sufficient to detect esophageal intubation, although esophageal intubation may be detected if the ET tube is clearly outside the air shadow of the trachea.

MANAGEMENT

Approach to Intubation

After it is determined that the patient requires intubation, an approach must be planned. The algorithm in Figure 1–3 assumes that a decision to intubate has been made and outlines such an approach. The approach is predicated on two key determinations that must be made before active airway management is begun.

The first determination is whether the patient is in cardiopulmonary arrest, or a state very near to arrest, and is predicted to be unresponsive to direct laryngoscopy. Such a patient (agonal, near death) is called a “crash airway” patient for the purposes of airway management and is managed by immediate intubation without use of drugs, supplemented by

single dose of succinylcholine if the attempt to intubate fails and the patient is not sufficiently relaxed.

The second determination is whether the patient represents a difficult intubation. If so, the difficult airway algorithm is used ( Figure 1–4 ). For all other cases, that is, for all patients who require ED intubation but who have neither a “crash airway” nor a difficult airway, rapid sequence intubation is recommended. RSI provides the safest and quickest method of achieving intubation in such patients. After administration of the RSI drugs, intubation attempts are repeated until the patient is intubated or a failed intubation is identified. If more than one intubation attempt is required, BMV is used between attempts. If the operator cannot maintain the oxygen saturation at 90% or greater, or at least stable if beginning below 90%, a failed airway exists. This is referred to as a “can't intubate, can't oxygenate” situation. In addition, if three attempts at direct laryngoscopy have been unsuccessful, a failed airway exists because subsequent attempts at laryngoscopy by the same operator are unlikely to succeed. The three failed laryngoscopy attempts are defined as those by an experienced operator, using optimal patient positioning and best possible technique. Also, if the operator ascertains after a single attempt that intubation will be impossible (e.g., grade IV laryngoscopic view despite optimal patient positioning), a failed airway is present.

The Difficult Airway

When preintubation evaluation has identified a potentially difficult airway, a different approach is used (see Figure 1–4 ). The approach is based on the fact that NMBAs should not be administered to a patient for intubation unless the operator believes that (1) intubation is likely to be successful and (2) BMV is likely to be successful if a first intubation attempt does not succeed.

The perception of a difficult airway is relative, and many ED intubations could be considered “difficult.” The judgment regarding whether to treat the airway as a typical emergency airway or whether to use the difficult airway algorithm is based on the degree of perceived difficulty and the individual circumstances of the case.

When a difficult airway approach is used, the first step is to ensure that oxygenation is sufficient to permit a planned, sequential approach (see Figure 1–4 ). If oxygenation is inadequate and cannot be made adequate by supplementation with bag and mask, the airway should be considered a failed airway. The failed-airway algorithm should be used because the predicted high degree of intubation difficulty combined with failure to maintain oxygen saturation is analogous to the “can't intubate, can't oxygenate” situation. When oxygenation is adequate, the first consideration is whether blind nasotracheal intubation (BNTI) might be appropriate. BNTI is a valuable technique for management of the difficult airway

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because it can be done while preserving the patient's spontaneous ventilation. It may be particularly useful in those infrequent situations when the airway difficulties are predominantly in the mouth (e.g., angioedema).

If BNTI is not chosen or is not successful, the next consideration is whether RSI is appropriate, based on the operator's assessment of the likelihood of (1) successful intubation and (2) successful ventilation if intubation is unsuccessful. In some cases a double setup can be used in which RSI is performed but all preparations are undertaken for rescue cricothyrotomy before the drugs are administered. If RSI is not advisable, an “awake” technique can be used. In this context, “awake” means that the patient continues to breathe and is able to respond to or interact with caregivers. Usually the technique involves sedation and topical anesthesia. As described later, these “awake” techniques include direct laryngoscopy, fiberoptic intubation, intubating laryngeal mask airway, lighted stylet, and (rarely) primary cricothyrotomy.

The Failed Airway

Management of the failed airway is dictated by whether or not the patient can be oxygenated. If adequate oxygenation cannot be maintained, the rescue technique of first resort is cricothyrotomy. Multiple attempts at other methods in the context of failed oxygenation will delay cricothyrotomy and may place the patient at increased risk for hypoxic brain injury. If an alternative device (e.g., lighted stylet, laryngeal mask airway) is readily at hand, however, it can be attempted simultaneously with preparations for immediate cricothyrotomy.

If adequate oxygenation is possible, several options are available for the failed airway. In almost all cases, cricothyrotomy is the definitive rescue technique for the failed airway if time does not allow for other approaches or if they fail. The fundamental difference in philosophy between the difficult airway and the failed airway is that the difficult airway is planned for, and the standard is to place a cuffed ET tube in the trachea. The failed airway is not planned for, and the standard is to achieve an airway that provides adequate oxygenation to avert the immediate problem of hypoxic brain injury. Thus some of the devices used in the failed airway (e.g., transtracheal jet ventilator, Combitube) are temporary and do not necessarily provide airway protection.

THERAPEUTIC MODALITIES

Methods of Intubation

Although many techniques are available for intubation of the emergency patient, four methods represent the majority of ED intubations.[1] [9]

Rapid Sequence Intubation

RSI is the cornerstone of modern emergency airway management and is defined as the virtually simultaneous administration of a potent sedative (induction) agent and an NMBA, usually succinylcholine (SCh), for the purpose of ET intubation. This approach provides optimal intubating conditions while minimizing the risk of aspiration of gastric contents.

The central concept of RSI is to take the patient from the starting point (e.g., conscious, breathing spontaneously) to a state of unconsciousness with complete neuromuscular paralysis, then to achieve intubation without interposed assisted ventilation. The risk of aspiration of gastric contents is significantly higher for patients who have not fasted before induction. Application of positive-pressure ventilation can cause air to pass into the stomach, resulting in gastric distention and increasing the risk of aspiration.[22] The purpose of RSI is to avoid positive-pressure ventilation until the ET tube is correctly placed in the trachea with the cuff inflated. This requires a preoxygenation phase, during which the nitrogen reservoir in the functional residual capacity (FRC) in the lungs is replaced with oxygen, permitting at least several minutes of apnea in the normal adult before oxygen desaturation to 90% will ensue.[23]

Use of RSI also facilitates successful ET intubation by causing complete relaxation of the patient's musculature, thus allowing better access to the airway.[24] Finally, RSI permits pharmacologic control of the physiologic responses to laryngoscopy and intubation, thus mitigating potential adverse effects. These effects include further intracranial pressure increase in response to the procedure and to the sympathetic discharge resulting from laryngoscopy.[5] [25]

RSI is a series of discrete steps; not every step is taken in every case, but every step should be considered ( Box 1–4 ).

Preparation

In the initial phase the patient is assessed for intubation difficulty (if not already done) and the intubation is planned, including dosages and sequence of drugs, tube size, and laryngoscope blade and size. Drugs are drawn up and labeled. All necessary equipment is assembled. All these patients require continuous cardiac monitoring and pulse oximetry. At least one and preferably two good-quality intravenous (IV) lines should be established. Redundancy is always desirable in case of equipment or IV access failure.

Preoxygenation

Administration of 100% oxygen for 5 minutes in a normal, healthy adult results in the establishment of an adequate oxygen reservoir to permit up to 8 minutes of apnea before oxygen desaturation to less than 90% occurs[23] ( Figure 1–5 ). The time to desaturation below 90% in children is considerably less. In both children and adults, preoxygenation is essential to the “no bagging” approach of RSI. If time is insufficient for a full 5-minute preoxygenation phase, eight vital capacity breaths using high-flow oxygen can achieve oxygen saturations and apnea times that match or exceed those obtained with traditional preoxygenation.[26]

Preoxygenation should be done in parallel with the preparation phase and can be started in the field for high-risk patients. Oxygen saturation monitors permit earlier detection of desaturation during laryngoscopy, but preoxygenation remains an essential step in RSI.

Pretreatment

During this phase, drugs are administered to mitigate the patient's presenting condition, underlying conditions, or the effects of the intubation. Such agents include lidocaine, which has been shown to attenuate adverse intracranial and reactive airway responses to laryngoscopy

Box 1-4. The Six “Ps” of RSI

Preparation

Preoxygenation

Pretreatment

Paralysis with induction

Placement of tube

Postintubation management

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and intubation; opioids, such as fentanyl, which can reduce the sympathetic response to intubation; atropine, to prevent SCh-associated bradycardia in children under 10 years old; and competitive NMBAs, given in a “defasciculating” or “precurarizing” dose when indicated. Although many variations are possible for pretreatment regimens in various conditions, pretreatment can be simplified to a few basic indications ( Table 1–1 ).[5] [25] [27] [28]

When possible, 3 minutes should elapse between the administration of the pretreatment drug and the administration of the induction drug and NMBA. If time is insufficient to wait 3 minutes, even a reduced time may provide some benefit. Evidence supporting the use of the pretreatment agents is conflicting and indications are relative.

Paralysis with Induction

In this phase a potent sedative agent is administered by rapid IV push in a dose capable of rapidly producing unconsciousness. This is immediately followed by rapid administration of an intubating dose of an NMBA, usually SCh. The patient should be positioned for intubation as consciousness is lost, and Sellick's maneuver should be initiated.[22] Sellick's maneuver is the application of pressure to the anterior cricoid cartilage, causing posterior displacement of the cartilage to occlude the esophagus and prevent passive regurgitation of gastric contents. If active vomiting occurs at any time, Sellick's maneuver should be discontinued to avoid possible esophageal rupture. Once neuromuscular blockade (NMB) is established, active vomiting is no longer possible. Although the patient is unconscious and apneic, BMV should not be initiated unless the patient is unable to maintain an oxygen saturation of 90%.

Placement of Tube

Approximately 45 seconds after the administration of SCh, the patient will be relaxed sufficiently to permit laryngoscopy. This is most easily assessed by moving the mandible to test for absence of muscle tone. The ET tube is placed under direct visualization of the glottis. If intubation is unsuccessful or if the cords are not visualized, the patient may be ventilated briefly with a bag and mask between attempts to reestablish the oxygen reservoir. In such cases, Sellick's maneuver must be continued; proper use of this maneuver during BMV of a paralyzed patient prevents passage of air into the stomach.[29] As soon as the ET tube is placed, the cuff should be inflated and its position confirmed

TABLE 1-1 -- Indications for Pretreatment Agents in RSI Drug: action Indications IV dose

Lidocaine: reduces intracranial response to laryngoscopy and bronchospastic response to laryngoscopy and intubation Patients with elevated intracranial pressure (ICP) or penetrating globe injury who are receiving succinylcholine; reactive airway disease 1.5 mg/kg

Fentanyl: reduces sympathetic (heart rate, blood pressure) response to laryngoscopy and intubation Elevated ICP, intracranial hemorrhage, berry aneurysm, ischemic heart disease, aortic dissection 3 μg/kg

Atropine: mitigates bradycardic response to succinylcholine Children under 10 years old 0.02 mg/kg

Vecuronium: defasciculates and mitigates ICP response to succinylcholine (may substitute pancuronium 0.01 mg/kg or rocuronium 0.06 mg/kg) Patients with elevated ICP or penetrating globe injury who are receiving succinylcholine 0.01 mg/kg

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TABLE 1-2 -- Sample RSI Using Etomidate and Succinylcholine Time Step

Zero minus 10 minutes Preparation

Zero minus 5 minutes Preoxygenation

100% oxygen for 5 minutes or eight vital capacity breaths

Zero minus 3 minutes Pretreatment

As indicated

Zero Paralysis with induction

Etomidate, 0.3 mg/kg

Succinylcholine, 1.5 mg/kg

Zero plus 45 seconds Placement

Sellick's maneuver

Laryngoscopy and intubation

End-tidal CO2 confirmation

Zero plus 2 minutes Postintubation management

Diazepam, 0.2 mg/kg plus

Pancuronium, 0.1 mg/kg, or

Vecuronium, 0.1 mg/kg

using an end-tidal CO2 detector. Auscultation of the lungs and epigastric area will help to detect mainstem or esophageal intubation. After confirmation of correct tracheal placement of the tube, Sellick's maneuver may be discontinued.

Postintubation Management

Tube placement within the trachea can be confirmed as described previously, and the tube secured in place. A chest radiograph should be obtained to confirm that mainstem intubation has not occurred and to assess the lungs. Long-acting NMBAs (e.g., pancuronium, vecuronium) are usually indicated and should be accompanied by adequate doses of a sedative agent (e.g., benzodiazepine). Mechanical ventilation should be initiated.

Table 1–2 presents a sample RSI protocol using etomidate and SCh.

Blind Nasotracheal Intubation

BNTI has been used extensively in both the ED and prehospital setting. Success rates have been about 80%.[30] High complication rates are reported, most often epistaxis or delayed or incorrect tube placement. Long-term complications (e.g., sinusitis, turbinate destruction, laryngeal perforation) are uncommon and related to multiple attempts or prolonged intubation. Basilar skull fracture and facial trauma have been considered contraindications to nasotracheal intubation to prevent entering the cranial vault or increasing the incidence of intracranial infection. This is not based on scientific study, however, and two studies have failed to detect a difference in complications between orally and nasally intubated facial trauma patients.[31] [32] Two prehospital studies have compared the success rates of RSI and nasotracheal intubation performed by physicians or paramedics on helicopter services. Results differed, with one study showing essentially equivalent success rates and the other showing a significant advantage for NMB over nasotracheal intubation.[33] [34] ED studies have demonstrated superiority of RSI over BNTI.[30] [35] Also, the incidence and severity of oxygen desaturation are increased in nasotracheal intubation compared with RSI.[36]

BNTI is a valid and useful method of intubation in the prehospital setting and is still widely used there. In the ED, where NMBAs and RSI are available, BNTI should be considered a second-line approach and reserved for patients in whom presence of a difficult airway makes RSI undesirable or contraindicated.

Awake Oral Intubation

Awake oral intubation is a deliberate technique in which sedative and topical anesthetic agents are administered to permit management of a difficult airway. Sedation and analgesia are achieved in a manner analogous to that for painful procedures in the ED. Topical anesthesia may be achieved by spray, nebulization, or local anesthetic nerve block. After the patient is sedated and topical anesthesia has been achieved, gentle direct or fiberoptic laryngoscopy is performed to determine whether the glottis will be visible and intubation will be possible. The patient may be intubated during the laryngoscopy, or the laryngoscopy may demonstrate that oral intubation will be possible, permitting safe use of RSI.

Awake oral intubation is distinct from the practice of oral intubation using a sedative or opioid agent to obtund the patient for intubation without NMB, which has been a typical ED practice. This latter technique can be referred to as “intubation with sedation alone,” or ISED. Proponents of ISED argue that administration of a benzodiazepine, opioid, or both to a patient provides improved access to the airway, decreases patient resistance, and avoids the risks inherent in NMB. However, this technique is actually more hazardous than RSI. Intubating conditions achieved even with deep anesthesia are significantly inferior to those achieved when NMB is used.[37] [38] [39] The same superiority of neuromuscular-assisted intubation over ISED has been observed in pediatric emergency medicine and in prehospital care.[40] [41]

In general the technique of administering a potent sedative agent to obtund the patient's responses and permit intubation in the absence of NMB is ill-advised and inappropriate for ET intubation in the ED.

Oral Intubation without Pharmacologic Agents

The unconscious, unresponsive patient may not require pharmacologic agents for intubation. In fact, if the patient is relaxed, administration of any pharmacologic agent, including an NMBA, may needlessly delay intubation. However, even the unconscious patient may retain sufficient muscle tone to render intubation difficult. If the glottis is not adequately visualized, administration of a single dose of SCh alone may facilitate laryngoscopy.

Pharmacologic Agents

Neuromuscular Blocking Agents

Muscle contraction is the result of membrane depolarization, which causes massive intracellular release of calcium ions from the sarcoplasmic reticulum, leading to active contraction of myofibrils. The inciting incident is the depolarization of portions of the myocyte membrane, called the motor end plates, that are adjacent to the innervating axons. Action potentials conducted down the innervating axons cause release of the neurotransmitter acetylcholine (ACh) from the terminal axon. The ACh traverses the synaptic cleft, binds reversibly to receptors on the motor end plate, and opens channels in the membrane to initiate depolarization.

NMBAs are highly water-soluble, quaternary ammonium compounds that mimic the quaternary ammonium group on the ACh molecule. Their water solubility explains why these

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11

Box 1-5. Conditions and Drugs that Reduce Pseudocholinesterase Activity

Pregnancy

Liver disease

Cancer

Cytotoxic drugs

Cholinesterase inhibitors

Drugs

Metoclopramide

Phenelzine

Others

agents do not readily cross the blood-brain barrier or placenta. The NMBAs are divided into two main classes. The depolarizing agents, of which SCh is the only one in broad clinical use, exert their effect by binding noncompetitively with ACh receptors on the motor end plate and causing sustained depolarization of the myocyte. The other major class of NMBA comprises the competitive, or nondepolarizing, agents, which bind competitively to ACh receptors, preventing access to ACh and thus preventing muscular activity. The competitive agents are of two pharmacologically distinct types, steroid-based agents and benzylisoquinolines. Each of these basic chemical types has distinct properties.

Succinylcholine

SCh is a chemical combination of two molecules of ACh. SCh is rapidly hydrolyzed by plasma pseudocholinesterase to succinylmonocholine, which is a weak NMBA, then to succinic acid and choline, which have no NMBA activity. Pseudocholinesterase is not actually present at the motor end plate and exerts its effects systemically before the SCh reaches the ACh receptor.[42] Thus only a small amount of the SCh that is administered survives to reach the motor end plate. Once attached to the ACh receptor, SCh is active until it diffuses away. Decreased plasma pseudocholinesterase activity can increase the amount of SCh reaching the motor end plate, thus prolonging SCh block. This occurs in two ways. Pseudocholinesterase activity can be reduced, or the enzyme can be (very rarely) genetically defective or deficient. The activity of the pseudocholinesterase is reduced in several conditions ( Box 1–5 ). [42] Reduced pseudocholinesterase activity is of little significance in the emergency setting because the prolongation of action is rarely significant, reaching only 23 minutes at the extreme.

Uses

SCh is rapidly active, typically producing intubating conditions within 60 seconds of administration by rapid IV bolus injection.[37] [38] [42] The clinical duration of action is 6 to 10 minutes, but adequate spontaneous respirations may occur within 5 minutes[23] (see Figure 1–5 ). Full recovery of normal neuromuscular function occurs within 15 minutes. The combination of rapid onset, complete reliability, short duration of action, and absence of serious side effects maintains SCh as the drug of choice for the majority of ED intubations.[1] [9] [43] The use of a competitive NMBA for RSI may be desirable when SCh is contraindicated and in certain other settings (see later discussion).

Cardiovascular effects

As an ACh analog, SCh binds to ACh receptors throughout the body, not just at the motor end

TABLE 1-3 -- Conditions and Periods of Concern Associated with Severe Hyperkalemia with Succinylcholine Administration Condition Period

Burns over more than 10% of body surface 48 hours to 6 months

Paralysis 3 days to 6 months

Denervation syndrome Until inactive for 6 months

Crush injuries 3 days to 6 months

Abdominal sepsis Longer than 3 days

plate. It is difficult to separate the effects of SCh on the heart that are caused by direct cardiac muscarinic stimulation from those caused by stimulation of autonomic ganglia by SCh and from those that are induced by the autonomic responses to laryngoscopy and intubation. SCh is a weak negative inotrope, which is not clinically significant. It is also a negative chronotrope, however, especially in children, and sinus bradycardia may ensue after SCh administration. This is prevented by prior administration of atropine, which is recommended for all children under 10 years of age and for adults when receiving a second dose of SCh. Other cardiac dysrhythmias, including ventricular fibrillation and asystole, have been attributed to SCh, but it is impossible to distinguish the effects of the drug itself from those caused by the intense vagal stimulation and catecholamine release that accompany laryngoscopy and intubation. In addition, many of these catastrophic complications occur in critically ill patients, further confounding attempts to identify whether the illness or any particular drug or procedure is the cause.

Fasciculations

The depolarizing action of SCh results in fine, chaotic contractions of the muscles throughout the body for several seconds at the onset of paralysis. Although fasciculations have been linked temporally to several adverse side effects of SCh, such as increases in intracranial pressure (ICP), intragastric pressure, and intraocular pressure (IOP), evidence of a cause-and-effect relationship is lacking.[44] Muscle pain occurs in many patients who receive SCh. Although it is widely believed that muscle pains are reduced or abolished by prior administration of a defasciculating dose of a competitive NMBA, the evidence is not conclusive.[45] Administration of a defasciculating dose of a competitive NMBA is desirable for certain patients, such as those with elevated ICP, but benefit in others is difficult to demonstrate. Thus abolition of fasciculation is primarily a cosmetic issue, and the decision is appropriately left to the individual clinician.

Hyperkalemia

SCh has been associated with severe, fatal hyperkalemia when administered in specific clinical circumstances ( Table 1–3 ). [46] Although the hyperkalemia may be severe and fatal, this effect does not occur until at least several days after the inciting injury or burn. Therefore hyperkalemia in these contexts is not usually a significant issue in the ED. SCh remains the agent of choice for RSI in acute burn, trauma, and intraabdominal sepsis patients if intubation occurs in less than 48 hours after onset of the condition. If doubt exists regarding the onset time, competitive

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12

RSI should be used. Denervation syndromes (e.g., multiple sclerosis) can be particularly troubling, however, since it is often not clear when the syndrome began or when progression halted. Stroke (cerebrovascular accident) also presents unique issues. Although there is debate whether stroke produces a “denervation” syndrome, fatal hyperkalemia has occurred in several patients with upper motor neuron lesions. The best course might be to avoid SCh in all patients who have had a stroke or at least in those who had the neurologic injury more than 3 days and less than 6 months before intubation. Hyperkalemia probably does not occur in other classes of patients receiving SCh and would not exceed 0.5 mEq/L if it did.[47] Therefore SCh is not contraindicated in renal failure but probably should not be used in patients known or suspected (e.g., missed dialysis) to have significant hyperkalemia before the intubation sequence is begun. Similarly, evidence of hyperkalemia on the 12-lead electrocardiogram (ECG) should suggest use of a competitive agent for RSI. The same rationale applies to patients with significant known or suspected rhabdomyolysis or acute renal failure.

Increased intraocular pressure

SCh may cause an increase in IOP. This may be a concern in ED patients with penetrating globe injuries, in whom increased IOP may promote extrusion of ocular contents. The rise in IOP is small, however, and is probably abolished by defasciculation, use of proper technique, and lidocaine pretreatment.[48] Alternatively, use of a competitive NMBA for RSI eliminates the need for either defasciculation or lidocaine pretreatment.

Masseter spasm

SCh has been reported rarely to cause masseter spasm, primarily in children.[42] The clinical significance of this phenomenon is unclear, but administration of a competitive NMBA terminates the spasm. Severe, persistent spasm should raise suspicion of malignant hyperthermia.

Malignant hyperthermia

SCh has been associated with malignant hyperthermia (MH), a perplexing syndrome of rapid temperature rise and aggressive rhabdomyolysis. MH occurs in genetically predisposed individuals under general anesthesia with certain volatile anesthetic agents or SCh. The condition is extremely rare and has not been reported in the context of ED intubation. Treatment consists of cessation of any potential offending agents; administration of dantrolene, 2 mg/kg intravenously (IV) every 5 minutes to a maximum dose of 10 mg/kg; and attempts to reduce body temperature by external means.[49] A national MH hot line is available for consultation at 209-634-4917 (ask for “index zero”).

Refrigeration

The standard recommendation to keep SCh refrigerated creates problems related to its storage, timely retrieval, and ready availability on intubation carts or kits in the ED. SCh undergoes degradation beginning at the time of manufacture, and the rate of this degradation is much lower when the drug is refrigerated. However, SCh retains more than 90% of its original activity when stored at room temperature for 3 months; it retains even more if protected from light.[50] Therefore SCh may be kept at room temperature in the ED, provided a proper inventory control system ensures that all supplies are replaced not more than 3 months after introduction.

Competitive Agents

Competitive NMBAs are classified according to their chemical structure. The steroid-based agents include pancuronium, vecuronium, rocuronium, and rapacuronium. The benzylisoquinolines include d-tubocurarine, atracurium, cisatracurium, mivacurium, doxacurium, and metocurine. Histamine release, which may be important in hemodynamically compromised patients and those with reactive airway disease, is caused by the benzylisoquinolines, primarily d-tubocurarine, but also occurs with rapacuronium.[42] Pancuronium is widely used because of its familiarity, absence of histamine release, and low cost. Although its muscarinic effects almost universally cause a modest tachycardia, this is rarely of consequence. Vecuronium neither releases histamine nor exhibits cardiac muscarinic blockade, so it has become popular despite its higher cost and the inconvenience of reconstituting it from powder with each use. Two newer steroidal agents, rocuronium and rapacuronium, have been advocated for RSI. Atracurium is advocated for use in patients with renal failure because its excretion is completely independent of renal function.

Rapid Sequence Intubation with a Competitive Agent

Competitive agents, especially vecuronium and, more recently, rocuronium and rapacuronium, have been extensively studied for RSI.[37] [38] [39] [51] Although vecuronium was the first competitive NMBA to clearly establish a role in RSI, the 0.3-mg/kg dose required to achieve rapid intubating conditions results in almost 2 hours of paralysis, making it less desirable for ED RSI.[37] [38] Rocuronium bromide, 1 mg/kg IV, achieves intubating conditions closely approaching those of SCh, lasts 40 to 60 minutes, and has been used in the ED with success.[52] The most promising competitive NMBA for use in ED RSI is the new agent, rapacuronium, approved by the U.S. Food and Drug Administration (FDA) in 1999. Rapacuronium, 1.5 mg/kg IV, achieves intubation level paralysis in a time comparable to that of SCh and can be reversed with neostigmine and glycopyrrolate to reestablish spontaneous ventilation in less than 10 minutes.[51] [53]

Table 1–4 presents a sample RSI protocol using etomidate and rocuronium or rapacuronium.

TABLE 1-4 -- Sample RSI Using Etomidate and Competitive NMBA Time Step

Zero minus 10 minutes Preparation

Zero minus 5 minutes Preoxygenation

100% oxygen for 5 minutes or eight vital capacity breaths

Zero minus 3 minutes Pretreatment

As indicated

Zero Paralysis with induction

Etomidate, 0.3 mg/kg

Rapacuronium, 1.5 mg/kg, or

Rocuronium, 1.0 mg/kg

Zero plus 45 seconds Placement

Sellick's maneuver

Laryngoscopy and intubation

Confirmation with end-tidal CO2

Zero plus 2 minutes Postintubation management

Diazepam, 0.2 mg/kg immediately plus Rapacuronium or rocuronium (one third of intubating dose as needed at signs of recovery of muscle function)

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13

Paralysis after intubation

After intubation, longer paralysis is usually desired for patient control and to permit mechanical ventilation. In most cases, one agent is comparable to another, and cost may be a consideration. Longer term NMB must not be undertaken without attention to appropriate sedation of the patient. An adequate dose of a benzodiazepine, such as diazepam, 0.2 mg/kg IV, is often the best initial choice for sedation accompanying use of longer-acting NMBAs.

Induction Agents

Virtually every patient who is receiving an NMBA for intubation requires a potent sedative to induce unconsciousness. Neuromuscular paralysis without sedation can lead to undesirable psychologic and physiologic effects. The patient who presents with any degree of clinical responsiveness, including reactivity to noxious stimuli, requires a sedative or induction agent at the time of administration of any NMBA. Patients who are already deeply unconscious and unresponsive may not require an induction agent if drugs or alcohol are the cause of the unconscious state. Patients who are unconscious because of a central nervous system (CNS) insult should always receive an induction agent to optimize the attenuation of adverse responses to airway manipulation. Induction agents also enhance the effect of the NMBA and improve intubating conditions, because the intubation is done at the earliest phase of NMB, and the relaxation effects of the induction agent are additive to those of the NMBA.[24]

Etomidate

Etomidate is an imidazole derivative that has been in use since 1972. It has a similar profile of activity to thiopental, with rapid onset, rapid peak activity, and brief duration, but is remarkably hemodynamically stable.[54] The induction dose is 0.3 mg/kg IV. Because etomidate is able to decrease ICP, cerebral blood flow (CBF), and cerebral metabolic rate (CMRO2 ) without adversely affecting systemic mean arterial blood pressure and thus cerebral perfusion pressure, it is an excellent induction agent for patients with elevated ICP, even with hemodynamic instability.[55] Etomidate has been reported to cause suppression of endogenous cortisol production, but not with single use or short periods of IV infusion.[56] Diminished response to adrenocorticotropic hormone (ACTH) challenge has been documented 24 hours after a single use of etomidate, but the clinical significance of this is not known.[57] Etomidate appears to have emerged as the agent of choice for ED RSI, and numerous reports attest to its effectiveness and safety.[1] [9] [56] [58]

Barbituates

Although both the thiobarbiturate sodium thiopental and the methylated oxybarbiturate methohexital have been used as induction agents for RSI, thiopental is the more widely used. These rapidly acting barbiturates are highly lipid soluble and readily cross the blood-brain barrier, acting on the gamma-aminobutyric acid (GABA) receptor neuroinhibitory complex to produce rapid depression of CNS activity. A single dose of 3 mg/kg of thiopental produces loss of consciousness in less than 30 seconds, has a peak effect at 1 minute, and has a clinical duration of 5 to 8 minutes. Methohexital may have a slightly shorter duration of action but is more prone to cause CNS excitatory side effects such as myoclonus. Thiopental is a negative inotrope and a potent venodilator and should be used with caution in patients whose cardiovascular reserve is diminished. For the same reason, thiopental should be avoided in the hypotensive patient who will not tolerate further compromise of circulation. Thiopental can release histamine and probably should not be used in asthmatic patients.

Benzodiazepines

Of the benzodiazepines, only midazolam is well suited to use as an induction agent, with a recommended dose of 0.1 to 0.3 mg/kg IV. In a dose of 0.2 mg/kg IV, midazolam produces loss of consciousness in about 30 seconds and has a clinical duration of 15 to 20 minutes.[59] Midazolam is a negative inotrope comparable to thiopental and should be used with caution in hemodynamically compromised patients and elderly persons, for whom the dose can be reduced to 0.1 or even 0.05 mg/kg. Onset is slower at these reduced doses. Much lower doses than indicated are often used in ED intubations, perhaps because practitioners are familiar with the sedation doses but not the anesthetic induction doses of midazolam.[60] These inadequate doses reduce the effectiveness of laryngoscopy, do not provide optimal blunting of adverse physiologic effects of laryngoscopy and intubation, and may compromise the patient's amnesia for the intubation. Midazolam is somewhat cerebroprotective, but less so than etomidate or thiopental.

Ketamine

Ketamine, a phencyclidine derivative, has been widely used as a general anesthetic agent since 1970. After an IV dose of 1.0 to 2.0 mg/kg, ketamine produces loss of consciousness within 30 seconds, peaks in approximately 1 minute, and has a clinical duration of 10 to 15 minutes. As a dissociative anesthetic agent, ketamine induces a cataleptic state rather than a true unconscious state. The patient has profound analgesia but may have open eyes. Many protective reflexes, including airway reflexes, will be preserved.

The principal use of ketamine in emergency airway management is for the induction of patients with asthma and hemodynamically unstable trauma patients without head injury. Ketamine is exceptionally hemodynamically stable, more so than etomidate, and this latter indication capitalizes on ketamine's superior cardiovascular stability.[59] [61] Controversy exists regarding the use of ketamine in patients with elevated ICP because ketamine has been documented to increase CMRO2 , ICP, and CBF. [62] There is conflicting evidence that ketamine can produce harm in this way, however, and its role as an induction agent in trauma is significant because of its superior hemod

[AZCEP]

This is vital information that every provider needs to have running through their mind when the time comes to secure/manage an airway.

While reading the information is good, the combination of the book with the course that goes with it, is invaluable. Take the opportunity when it comes to your area and lay out the money to attend.

The SLAM conference in Dallas is another excellent resource. If you are in the Dallas area in April/May, you will not find a better way to spend some time making yourself better at something your patients can't live without.

[Ace844]

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

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10 R.S. Cormack and J. Lehane, Difficult tracheal intubation in obstetrics, Anaesthesia 39 (1984), pp. 1105–1111. Abstract-MEDLINE | Abstract-EMBASE

11 S.M. Yentis and D.J.H. Lee, Evaluation of an improved scoring system for the grading of direct laryngoscopy, Anaesthesia 53 (1998), pp. 1041–1044. Abstract-MEDLINE | Abstract-EMBASE | Full Text via CrossRef

12 L.K. Koh, C.E. Kong and P.C. Ip-Yam, The modified Cormack–Lehane score for the grading of direct laryngoscopy: evaluation in the Asian population, Anaesthesia and Intensive Care 30 (2002), pp. 48–51. Abstract-MEDLINE | Abstract-EMBASE

13 R.M. Levitan, E.A. Ochroch and S. Kush et al., Assessment of airway visualisation: validation of the percentage of glottic opening (POGO) scale, Academic Emergency Medicine 5 (1998), pp. 919–923. Abstract-MEDLINE | Abstract-EMBASE

14 F. Adnet, S.W. Borron and S.X. Racine et al., The intubation difficulty scale (IDS): proposal and evaluation of a new score characterizing the complexity of endotracheal intubation, Anesthesiology 87 (1997), pp. 1290–1297. Abstract-EMBASE | Abstract-MEDLINE | Full Text via CrossRef

15 F. Adnet, S.X. Racine and S.W. 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

[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

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64 S.J. Piha and J.P. Halonen, Infrared pupillometry in the assessment of autonomic function, Diabetes Research and Clinical Practice 26 (1994), pp. 61–66. Abstract

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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

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69 W.R. Taylor, J.W. Chen and H. Meltzer et al., Quantitative pupillometry, a new technology: normative data and preliminary observations in patients with acute head injury. Technical note, Journal of Neurosurgery 98 (2003), pp. 205–213. Abstract-MEDLINE | Abstract-Elsevier BIOBASE | Abstract-EMBASE

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76 B.A. Coda, M.C. Brown and R. Schaffer et al., Pharmacology of epidural fentanyl, alfentanil, and sufentanil in volunteers, Anesthesiology 81 (1994), pp. 1149–1161. Abstract-MEDLINE | Abstract-EMBASE

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84 J. Emery, D. Ho and L. 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

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[Ace844]

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

The principal use of ketamine in emergency airway management is for the induction of patients with asthma and hemodynamically unstable trauma patients without head injury. Ketamine is exceptionally hemodynamically stable, more so than etomidate, and this latter indication capitalizes on ketamine's superior cardiovascular stability.[59] [61] Controversy exists regarding the use of ketamine in patients with elevated ICP because ketamine has been documented to increase CMRO2 , ICP, and CBF. [62] There is conflicting evidence that ketamine can produce harm in this way, however, and its role as an induction agent in trauma is significant because of its superior hemodynamic stability.[59] Ketamine tends to produce unpleasant emergence phenomena, especially disturbing or frightening dreams in the first 3 hours after awakening. These reactions, which are more prominent in adults than in children, in women than in men, in patients receiving larger doses, and in certain personality types, are controllable by benzodiazepine administration. Patients (e.g., with asthma) who undergo RSI with ketamine should receive a sufficient dose of a benzodiazepine, such as 0.05 mg/kg of lorazepam or 0.2 mg/kg of diazepam, as part of their postintubation management.

Special Clinical Circumstances

Status Asthmaticus

Status asthmaticus with supervening respiratory failure is a preterminal event. Respiratory failure in the asthmatic patient is not caused primarily by progressive worsening of the bronchospasm, but rather by eventual exhaustion and fatigue secondary to prolonged effort of breathing against severe airway resistance. Thus all patients who are intubated for status asthmaticus will be heavily sedated and paralyzed and will receive mechanical ventilation. RSI permits the most rapid attainment of

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intubation, protects against aspiration, and induces the unconsciousness and motor paralysis necessary for mechanical ventilation; it is the superior technique for intubation of the patient in status asthmaticus. BNTI takes longer, results in greater desaturation of oxygen, and has a higher complication and lower success rate than RSI[35] [36] ; it should be reserved for rare cases with compelling reasons to avoid NMB. Difficult airway considerations are complex in the asthmatic patient because of impending respiratory arrest and the patient's inability to tolerate attempts at awake intubation. Even when a difficult airway is identified in the asthmatic patient, RSI is the intubation method of choice, with a double setup for rescue cricothyrotomy when indicated.

The asthmatic patient has highly reactive airways, and steps should be taken to minimize any additional bronchospasm that may occur during intubation. Lidocaine has been shown to suppress the coughing that occurs in response to airway manipulation and may improve ET tube tolerance and reduce reactive bronchospasm in asthmatic patients.[27] Therefore lidocaine, 1.5 mg/kg, is indicated as a pretreatment drug before intubation in status asthmaticus and in asthmatic patients being intubated for reasons other than their asthma. High dose inhaled β-agonists may provide maximal protection against reactive bronchospasm during intubation in asthmatics, and lidocaine may provide little additional benefit in this setting.[63] However, this has not been tested in patients in status asthmaticus. Ketamine has been shown to produce bronchodilation in both humans and animal models and may be the ideal induction agent in asthma. Although reports to date have been limited, there is a growing body of experience with ketamine as an induction agent for the emergency intubation of patients with status asthmaticus. Ketamine has also been reported to mitigate bronchospasm in patients who are not intubated and in patients who are already intubated and who are not improving with mechanical ventilation ( Table 1–5 ).

TABLE 1-5 -- RSI for Status Asthmaticus Time Step

Zero minus 10 minutes Preparation

Zero minus 5 minutes Preoxygenation (as possible)

Continuous albuterol nebulizer 100% oxygen for 5 minutes or eight vital capacity breaths

Zero minus 3 minutes Pretreatment

Lidocaine, 1.5 mg/kg

Zero Paralysis with induction

Ketamine, 1.5 mg/kg

Succinylcholine, 1.5 mg/kg

Zero plus 45 seconds Placement

Sellick's maneuver

Laryngoscopy with intubation

End-tidal CO2 confirmation

Zero plus 2 minutes Postintubation management

Diazepam, 0.2 mg/kg

Pancuronium, 0.1 mg/kg, or

Vecuronium, 0.1 mg/kg

In-line albuterol nebulization

Additional ketamine as indicated

.

Hemodynamic Consequences of Intubation

Laryngoscopy and intubation are potent stimuli for the reflex release of catecholamines.[64] This reflex sympathetic response to laryngoscopy (RSRL) produces only modest increases in blood pressure (BP) and heart rate (HR) and is of little consequence in otherwise healthy patients. The RSRL is of potential clinical significance in two settings: acute elevation of ICP and certain cardiovascular diseases (e.g., intracerebral hemorrhage, subarachnoid hemorrhage, aortic dissection or aneurysm, ischemic heart disease). In these settings the reflex release of catecholamines, increased myocardial oxygen demand, and attendant rise in mean arterial blood pressure (MABP) and HR may produce deleterious effects. The synthetic opioids (e.g., fentanyl) and beta-adrenergic blocking agents (e.g., esmolol) are capable of blunting the RSRL and stabilizing HR and BP during intubation. Lidocaine has also been studied, but the results are contradictory and inconclusive.[25] In patients at risk from acute BP elevation, administration of fentanyl, 3 μg/kg, during the pretreatment phase of RSI attenuates the HR and BP rise. The full sympatholytic dose of fentanyl is 5 or 6 μg/kg, but if this dosage is administered as a single pretreatment bolus, hypoventilation or apnea can occur. The administration of 3 μg/kg is safer and can be supplemented with an additional 3 μg/kg immediately after the SCh if full sympathetic blockade is desired or if hypertension and tachycardia ensue, providing evidence of excessive sympathetic activity. Fentanyl should be given as the last pretreatment drug over at least 60 seconds to prevent hypoventilation or apnea.

Elevated Intracranial Pressure

When ICP is elevated as a result of head injury or acute intracranial catastrophe, maintenance of cerebral perfusion pressure (CPP) and avoidance of further increases in ICP are desirable.[5] Significant reductions in MABP decrease CPP by reducing the driving gradient between arterial pressure and intracranial pressure, leading to increased cerebral ischemia.[5] [65] Maintenance of the systemic MABP at 100 mm Hg or higher supports the CPP and reduces the likelihood of secondary injury. In addition, cerebral autoregulation may be lost, and increases in systemic BP may lead to corresponding increases in CBF and thus ICP. Therefore, with elevated ICP, control of the reflex hemodynamic stimulation resulting from intubation is desirable to avoid further elevation of ICP. Fentanyl, 3 μg/kg given as a pretreatment drug, is the best choice for this purpose.[5]

Evidence suggests a separate reflex that increases ICP in response to laryngoscopy and intubation, although the precise mechanism is not understood. IV lidocaine reduces ICP and blunts the ICP response to laryngoscopy and intubation.[27] [66] Therefore lidocaine, 1.5 mg/kg IV during the pretreatment phase of RSI, is desirable to blunt the ICP response to laryngoscopy and intubation. Similarly, the RSRL and ICP response to laryngoscopy and intubation relatively contraindicate BNTI, which should be undertaken only if RSI is not possible.[67]

SCh may induce a rise in ICP.[68] Prior administration of a defasciculating dose of a competitive NMBA greatly reduces or abolishes this response.[69] Although pretreatment administration of a “mini” dosage of SCh has been shown to abolish fasciculation effectively, no evidence indicates that this technique protects against the potential ICP rise with SCh.[70] An alternative approach would be to substitute either rapacuronium (1.5 mg/kg) or rocuronium (1.0 mg/kg) for SCh in

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RSI, thus avoiding the need for a defasciculating agent. The physician should choose an induction agent that balances a favorable effect on cerebral dynamics and ICP with a stable systemic hemodynamic profile. At present, etomidate (0.3 mg/kg) probably is the best choice for patients with elevated ICP, although thiopental also would be an excellent choice when hypotension is not present ( Table 1–6 ).

Potential Cervical Spine Injury

Few issues in modern emergency care have been more controversial than the safety, or lack of safety, of various methods proposed to achieve intubation of the trachea in patients who are known or suspected to have unstable injury of the cervical spine.[71] [72] Historically, it was believed that oral ET intubation carried an unacceptably high risk of injury to the cervical spinal cord and was therefore relatively contraindicated, but this assertion was never subjected to scientific scrutiny. Since then, numerous studies and reports have asserted the safety and effectiveness of controlled, oral intubation with in-line cervical spine immobilization, whether done as an awake procedure or with NMB.[73] [74] [75] Thus the evidence favors RSI with in-line stabilization, which provides maximal control of the patient, the ability to mitigate adverse effects of the intubation, and the best conditions for laryngoscopy. In-line stabilization also appears to improve the laryngoscopic view of the larynx compared with conventional tape/collar/sandbag immobilization.[74] [75] Use of the Bullard laryngoscope, a rigid, fiberoptic laryngoscope, reduces the amount of cervical spine movement during oral intubation of uninjured, elective anesthesia patients, which should protect the injured spine.[76]

Cervical spine immobilization of patients with penetrating head and neck trauma is poorly addressed in the literature.[77] It is uncertain whether patients with gunshot or shotgun injuries to the head or neck are at risk of exacerbation of

TABLE 1-6 -- RSI for Elevated Intracranial Pressure Time Step

Zero minus 10 minutes Preparation

Zero minus 5 minutes Preoxygenation

100% oxygen for 5 minutes or eight vital capacity breaths

Zero minus 3 minutes Pretreatment

Vecuronium, 0.01 mg/kg *

Lidocaine, 1.5 mg/kg

Fentanyl, 3 μg/kg (slowly)

Zero Paralysis with induction

Etomidate, 0.3 mg/kg

Succinylcholine, 1.5 mg/kg *

Zero plus 45 seconds Placement

Sellick's maneuver

Laryngoscopy with intubation

End-tidal CO2 confirmation

Zero plus 2 minutes Postintubation management

Fentanyl, 3 μg/kg (optional)

Diazepam, 0.2 mg/kg

Vecuronium, 0.1 mg/kg or

Pancuronium, 0.1 mg/kg

* May substitute rocuronium, 1.0 mg/kg, or rapacuronium, 1.5 mg/kg, for succinylcholine. If so, omit vecuronium dose during pretreatment phase.

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cervical cord injury during intubation, but there is no report of such a patient, without spinal neurologic injury, who was injured by intubation. Prudence would dictate immobilization of patients with gunshot wounds to the neck and those with gunshot wounds to the head and secondary injury (e.g., fall from height) or with neurologic deficit suggesting spinal involvement. Immobilization of patients with penetrating injury elsewhere in the body should be directed by the likelihood of secondary injury to the spine from a fall or other event distinct from the wounding.

Pediatric Intubation

Although many considerations in pediatric intubation are the same as for adults, a few differences exist in regard to airway management. The larynx is higher in the child's neck, causing a more acute angle between the oral pharynx and the larynx. Visualization is aided by gentle posterior pressure on the anterior aspect of the thyroid cartilage. The epiglottis is high and very soft, again making visualization of the cords more difficult. If the child is very small, the prominent occiput brings the mouth to a position far anterior to the larynx; an assistant can lift the chest gently by grasping both shoulders, immobilizing the head at the same time. The airway in the small child is very short, and care must be taken not to intubate either bronchus.

A straight laryngoscope blade is desirable, especially in very young children, and positioning for intubation may be different. BNTI is relatively contraindicated in children under 12 years old. Although the product insert for SCh now advises against its routine use in pediatric anesthesia, because of fatal hyperkalemia in children with undiagnosed congenital neuromuscular disorders (e.g., muscular dystrophy), it remains the drug of choice for emergency RSI of infants and children.[78] Both rocuronium and rapacuronium have been used in children, but experience is too limited to recommend that they replace SCh for pediatric RSI in the ED. RSI may be used in children in a similar manner to adults, with two important differences. Excessive bradycardia may be seen with Sch in children under 10 years old, and this is prevented by administration of atropine (0.02 mg/kg) during the pretreatment phase. The dose of SCh in infants is 2 mg/kg. Induction agents may be selected using similar criteria as for adults. Successful RSI using vecuronium through an intraosseous needle has been reported.[79] Cricothyrotomy is impossible in small children and alternative rescue airway devices (e.g., percutaneous transtracheal jet ventilation) are required.

Methods for the Difficult or Failed Airway

Regardless of the care taken by the intubator and the detailed assessment of the patient before intubation, some intubations will simply be unsuccessful or impossible. In most circumstances when intubation is not possible, BMV will provide adequate ventilation and oxygenation until a rescue airway can be established. This underscores the importance of evaluating the patient for ease of both intubation and ventilation before deciding on the best approach and initiating the intubation sequence.[8] [10] Several airway options are available in the event of a difficult or failed intubation.

Special Airway Devices

Bullard Laryngoscope

The Bullard laryngoscope (BL) is a rigid, fiberoptic instrument recommended for intubation of the difficult airway. The scope has a long, smoothly curved blade with a fiberoptic channel and a suction port

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Figure 1-6 Bullard laryngoscope. A, Laryngoscope blade with fiberoptic viewing port (arrow). B, Laryngoscope blade with stylet attached and endotracheal tube loaded.

( Figure 1–6 ). The BL has an attached, dedicated intubating stylet, so that laryngoscope and ET tube are inserted together as a unit. Visualization of the glottis is through the fiberoptic port, so limitations of cervical spine movement or mouth opening do not impair Bullard laryngoscopy to the same extent that they compromise conventional laryngoscopy.[76] The BL has been used successfully when intubation was anticipated to be difficult or when other attempts had failed.[76] [80] Without more controlled, prospective studies, it is impossible to assess the true success rate. The BL also has been used for awake intubation.[81] Intubation can be achieved with less cervical spine movement than in standard laryngoscopy with MacIntosh or Miller blades, but it is uncertain whether this “advantage” translates into enhanced protection of the injured cervical spine.[76] As with all devices and techniques, there is a significant learning curve for the BL, and training needs should be anticipated to match those for conventional fiberoptic intubation. The BL has been used successfully in ED trauma patients.[82]

Laryngeal Mask Airway

The laryngeal mask airway (LMA) is an irregular, ovoid, silicone mask with an inflatable rim, connected to a tube that allows ventilation ( Figure 1–7 ). The mask is blindly inserted into the pharynx, then inflated, providing a seal that permits ventilation of the trachea with minimal gastric insufflation. In elective anesthesia the LMA has an extremely high insertion success rate and low complication rate, including a very low incidence of tracheal aspiration.[83] In the emergency setting, studies to date have focused on use during resuscitation from cardiopulmonary arrest. Evaluations of LMA insertion by both experienced and inexperienced personnel have consistently demonstrated ease of insertion, high insertion success rates, and successful ventilation.[84] [85] The LMA may be a viable alternative to ET intubation for in-hospital cardiac arrest, particularly when responders are inexperienced airway managers.[84] At a

Figure 1-7 Laryngeal mask airway (LMA). A, Frontal view; B, side view.

Figure 1-8 Intubating laryngeal mask airway (I-LMA). Courtesy LMA North America, Inc, San Diego.

minimum, the device may serve a temporizing role equal or superior to BMV until definitive airway management can be achieved.

The intubating laryngeal mask (ILM) is designed to facilitate intubation through the mask after correct placement ( Figure 1–8 ). It differs from the LMA in two main ways: the mask is attached to a rigid, stainless steel ventilation tube that is bent almost to a right angle, and the mask incorporates an epiglottis elevator at its distal end. Placement of the ILM results in successful ventilation in almost 100% of cases and successful subsequent intubation in 95%.[86] [87] The ILM has a special ET tube and stabilizer rod to remove the mask over the ET tube after intubation is accomplished.

At present the primary use of the LMA in the ED should be as a rescue technique to provide a temporary airway when intubation has failed, bag ventilation is satisfactory, and the patient has been paralyzed or is otherwise in need of immediate airway management. In such cases the LMA is one of a number of acceptable techniques, including lighted-stylet intubation and cricothyrotomy. Availability of the LMA and adequate prior training of the operator offer a legitimate option for the management of the failed airway. In addition, the ILM can be rapidly placed simultaneously with preparation for cricothyrotomy in the “can't intubate, can't oxygenate”

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Figure 1-9 Use of lighted-stylet device. The sharp right-angle bend (large arrow) facilitates transillumination of the neck (small arrow) when the trachea is entered. Courtesy Laerdal Medical Corporation.

scenario, as long as attempts to use the ILM do not delay cricothyrotomy. In the ED the ILM seems preferable to the LMA, since it can provide both ventilation and a high likelihood of intubation.

Lighted Stylet

The lighted stylet is a device that incorporates a handle, a fitting for mounting an ET tube, and an intubating stylet with a fiberoptic light mounted on the end ( Figure 1–9 ). The device is used like a conventional intubating stylet, but transillumination of the soft tissues from within the neck permits identification of tracheal entry by the stylet and ET tube. The lighted stylet has been used for both oral and nasal intubation and has an excellent success rate.[88] The lighted stylet is less stimulating to the HR and BP than conventional laryngoscopy and thus may be useful when sympathetic stimulation is not desirable.[89] As a device for a difficult or failed airway, the lighted stylet can be used as the intubating stylet for a standard oral intubation. The direct illumination by the stylet can aid in visualization during intubation. If direct laryngoscopy is unsuccessful, the first rescue procedure could be an immediate attempt at blind, oral intubation using the lighted stylet.

Esophagotracheal Combitube

The Combitube is a plastic double-lumen tube with one lumen functioning as an esophageal airway and the other lumen functioning as a tracheal airway. The tube is placed blindly into the esophagus, and proximal and distal balloons are inflated to prevent escape of ventilatory gases through the pharynx to the mouth or nose or down the esophagus. The tube is placed into the esophagus, as designed, almost 100% of the time, but both lumens are patent, so ventilation is still possible if the tube has been inadvertently placed into the trachea.

The Combitube is primarily a substitute for ET intubation used by non-ET-trained personnel.[90] [91] It has also been used as a rescue device or as a primary intubating device in difficult airways that have precluded ET intubation, but most studies have focused on subjects in full cardiopulmonary arrest.[91] Standard methods for confirming tube placement, using end-tidal CO2 , appear to be reliable in identifying whether the tube has been passed into the esophagus or trachea and in confirming the correct ventilation port.[90]

Although the Combitube has provided successful ventilation for several hours, it should be considered a temporizing measure only. Current use in the ED should be restricted to rescue placement after failed oral intubation with adequate BMV or a quick maneuver in the “can't intubate, can't oxygenate” patient simultaneous with preparation for a cricothyrotomy. The Combitube has virtually no role as a primary airway management device, except in cardiopulmonary arrest when expertise for ET intubation is not available, as in some prehospital care systems.[91]

Retrograde Intubation

In retrograde intubation (RI) a flexible wire is passed in retrograde fashion through a cricothyroid membrane puncture. The wire is retrieved through the mouth, then used to facilitate intubation by serving as a guide over which the ET tube is passed. Purported advantages of RI include ease of learning and application to the difficult airway.[92] High success rates are claimed, and RI may be useful when the upper airway is disrupted by trauma, rendering oral intubation difficult or impossible. Published reports of its use in emergency circumstances have been limited to case reports, very small series, and review articles. It is doubtful whether RI would be the airway maneuver of first choice in the ED, but it may be a useful consideration in unique difficult airway cases.

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Fiberoptic Intubation

Fiberoptic intubation (FOI) is widely used in the operating room for difficult airway cases, but its use is more variable in EDs. The intubating fiberoptic bronchoscope can be passed through the vocal cords under fiberoptic visualization, then can serve as an introducer over which the ET tube is passed. The advantage of FOI is simultaneous airway assessment and intubation; for example, in a patient with smoke inhalation, examination with the fiberoptic scope might identify that intubation is not required. FOI also can be used to complete the intubation if airway injury is identified. ED experience is limited.

Needle Cricothyrotomy with Transtracheal Jet Ventilation

Needle cricothyrotomy involves the insertion of a large needle (ideally 10 gauge) through the cricothyroid membrane into the airway. Once inserted, the needle is used to ventilate the patient with a standard wall oxygen source. Because of the high-velocity ventilation that ensues through the narrow catheter, this procedure is known as transtracheal jet ventilation (TTJV). TTJV has been used successfully in humans and has been subjected to various animal experiments to determine its uses and limitations.[93] The jet ventilator should include a regulator and gauge so that pressures can be monitored and reduced, especially in children. An internal catheter diameter of at least 2.5 mm is required in adults for ventilation to be maintained using a standard ventilation bag.[93] Upper airway obstruction has been considered a contraindication to TTJV, but ventilation can still be successful, although at the cost of higher intrapleural pressure and possibly pulmonary barotrauma. In general, when upper airway obstruction is present in adults, percutaneous or surgical cricothyrotomy is preferred.

The primary indication for TTJV in the ED is the initiation of emergency ventilation for a patient who is apneic (either because of the presenting condition or because of administration of an NMBA) and in whom both intubation and BMV are impossible. In such cases a decision should be made whether a surgical cricothyrotomy should be performed immediately or whether TTJV is a reasonable temporizing measure. Cricothyrotomy is extremely difficult or impossible in children under 10 years of age, and TTJV should be considered the surgical rescue modality of choice in this age group.[94] Although indications are uncommon, TTJV can be lifesaving ( Figure 1–10 ).

Cricothyrotomy

Cricothyrotomy is the creation of an opening in the cricothyroid membrane through which a cannula, usually a cuffed tracheostomy tube, is inserted to permit ventilation.[94] When surgical airway management is required, cricothyrotomy is the procedure of choice in the emergency setting, where it is faster, more straightforward, and more likely to be successful than tracheotomy.

Cricothyrotomy is indicated when oral or nasal intubation is impossible or fails and when BMV cannot maintain adequate oxygen saturation. The procedure may also be required when intubation fails and airway protection is important (e.g., upper airway hemorrhage with need for a protected airway). Several large series have established that the incidence of cricothyrotomy is approximately 1% of all ED intubations.[1] [9] Cricothyrotomy is relatively contraindicated by distorted neck anatomy, preexisting infection, and coagulopathy; these contraindications are relative, however, and the establishment of the airway takes precedence over all

Figure 1-10 Transtracheal jet ventilation (TTJV) setup. High-pressure ventilation tubing (dark triangle) attaches to standard wall oxygen outlet at 55 psi. Ventilation block (large arrow) is used to control oxygen flow through tubing (open triangle) to catheter (small arrow), which is inserted in the airway.

TABLE 1-7 -- Intubation Methods and Success Rates Method Percentage of all intubations Success rate

RSI 67% 99%

Oral, sedation only 7% 92%

Oral, no medications 18% 93%

BNTI 7% 86%

Data from National Emergency Airway Registry (NEAR II) Study.

other considerations. Successful cricothyrotomy after systemic fibrinolytic therapy has been reported.[95] The procedure should be avoided in children under 10 years of age, in whom anatomic considerations make it exceedingly difficult.[94]

Cricothyrotomes are devices used to perform percutaneous cricothyroidotomy. Percutaneous cricothyrotomy using the Seldinger technique may be comparable to formal surgical cricothyrotomy and may be easier to perform.[96] The safety and effectiveness of cricothyrotomes are not clearly established, however, and none is capable of placing a cuffed tube in the trachea. At present, cricothyrotomes, including those used with the Seldinger technique, should be considered as limited alternatives to formal, surgical cricothyrotomy, which can be quickly and successfully performed in most patients who require it.

OUTCOMES

Few studies of emergency airway management have characterized complications and outcomes. The largest single-institution series reported a success rate for ED RSI of 99% and a complication rate of 9.3%; most complications were minor.[1] Two larger multicenter series from the National Emergency Airway Registry (NEAR) of more than 6000 patients report success rates of greater than 98% for ED RSI.[9] [30] Table 1–7 lists success rates for the various airway management modalities in more than 4800 patients.

The definition of a “complication” for ED intubation is also evolving, and many occurrences identified during intubation might more accurately be tracked as “events.” For example, if a pneumothorax is identified after intubation of a patient with status asthmaticus, is the pneumothorax caused by the intubation or by the asthma?[97] Reclassification of complications as events will permit more appropriate analysis of intubation outcomes in the future. In the NEAR study the immediate complication rate was 3.5%; these are complications attributable to the intubation.[9] [30] No studies have evaluated the long-term outcome of intubated ED patients.

KEY CONCEPTS

• The decision to intubate is often based on what is anticipated to happen rather than simply the patient's current condition. Knowledge of the clinical course of the patient's condition and anticipation of possible deterioration is crucial, especially if the patient is to leave the ED for a time (e.g., interfacility transfer, diagnostic testing).

• Assessment of the patient for potential difficulty with intubation, bag-mask ventilation, or both is an essential step in planning airway management.

• In the absence of a “crash” patient (agonal, unresponsive to laryngoscopy) or a difficult airway, rapid sequence intubation (RSI) is the airway management method of choice for ED patients.

• Succinylcholine remains the neuromuscular blocking agent of choice for ED RSI but must be avoided in certain patient groups because of risk of significant hyperkalemia.

• Pretreatment drugs given during RSI can mitigate the adverse responses to intubation and improve the patient's clinical condition.

• Tube placement confirmation using end-tidal CO2 is essential after intubation, and failure to detect adequate quantities of exhaled CO2 is evidence of esophageal intubation until proved otherwise.

• When intubation is unsuccessful, various rescue strategies and devices can be used. In the “can't intubate, can't oxygenate” situation, immediate cricothyrotomy is the rescue method of choice.

REFERENCES

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44. Kovarik WD et al: Succinylcholine does not change intracranial pressure, cerebral blood flow velocity, or the electroencephalogram in patients with neurologic injury, Anesth Analg 78:469, 1994.

45. McLoughlin C et al: Muscle pains and biochemical changes following suxamethonium administration after six pretreatment regimens, Anaesthesia 47:202, 1992.

46. Cooperman LH, Strobel GE Jr, Kennell EM: Massive hyperkalemia after administration of succinylcholine, Anesthesiology 32:161, 1970.

47. Minton MD, Stirt JA, Bedford RF: Serum potassium following succinylcholine in patients with brain tumours, Can Anaesth Soc J 33:328, 1986.

48. Abdulla WY, Flaifil HA: Intraocular pressure changes in response to endotracheal intubation facilitated by atracurium or succinylcholine with or without lidocaine, Acta Anaesthesiol Belg 43:91, 1992.

49. Gronert GA, Antognini JF, Pessah IN: Malignant hyperthermia. In Miller RD et al, editors: Anesthesia, ed 5, London, 2000, Churchill Livingstone.

50. Schmutz DW, Muhlebach SF: Stability of succinylcholine chloride injection, Am J Hosp Pract 48:501, 1991.

51. Miguel R et al: Evaluation of neuromuscular and cardiovascular effects of two doses of rapacuronium (ORG9487) versus mivacurium and succinylcholine, Anesthesiology 91:1648, 1999.

52. Sakles JC et al: Rocuronium for rapid sequence intubation of emergency department patients, Ann Emerg Med 32:S13, 1998.

53. Purdy R et al: Early reversal of rapacuronium with neostigmine, Anesthesiology 91:51–57, 1999.

54. Weiss-Bloom LJ, Reich DL: Haemodynamic responses to tracheal intubation following etomidate and fentanyl for anaesthetic induction, Can J Anaesth 39:780, 1992.

55. Modica PA, Tempelhoff R: Intracranial pressure during induction of anaesthesia and tracheal intubation with etomidate-induced EEG burst suppression, Can J Anaesth 39:236, 1992.

56. Deonicke AW et al: A comparison of cardiac, stress, and recovery outcomes: etomidate versus propofol, Anesthesiology 89(3AS):20A, 1998.

57. Absalom A, Pledger D, Kong A: Adrenocortical function in critically ill patients 24 hours after a single dose of etomidate, Anaesthesia 54:861–867, 1999.

58. Tayal VS et al: Rapid-sequence intubation at an Emergency Medicine residency: success rate and adverse events during a two-year period, Acad Emerg Med 6:31, 1999.

59. Reves JG, Glass PSA, Lubarsky DA: Nonbarbiturate intravenous anesthetics. In Miller RD et al, editors: Anesthesia, ed 5, London, 2000, Churchill Livingstone.

60. Sagarin MJ et al: Underdosing of midazolam in emergency endotracheal intubation, J Emerg Med 2001 (in press).

61. Schneider RE: Sedatives and induction agents. In Walls RM et al, editors: Manual of emergency airway management, Philadelphia, 2000, Lippincott/Williams & Wilkins.

62. Albanese J et al: Ketamine decreases intracranial pressure and EEG activity in traumatic brain injury patients during propofol sedation, Anesthesiology 87:1328–1334, 1997.

63. Maslow A et al: Inhaled albuterol but not intravenous lidocaine protects against intubation-induced bronchoconstriction in asthma, Anesthesiology 93:1198–1204, 2000.

64. Shribman AJ, Smith G, Achola J: Cardiovascular and catecholamine responses to laryngoscopy with and without tracheal intubation, Br J Anaesth 50:295, 1987.

65. Woster PS, LeBlanc KL: Management of elevated intracranial pressure, Clin Pharmacol 9:762, 1990.

66. Nagao S et al: The effect of intravenous lidocaine on experimental brain edema and neural activities, J Trauma 12:1650, 1988.

67. Dohi S et al: End-tidal carbon dioxide monitoring during awake blind nasotracheal intubation, J Clin Anesth 2:415, 1990.

68. Minton MD et al: Increases in intracranial pressure from succinylcholine: prevention by prior nondepolarizing blockade, Anesthesiology 65:165, 1986.

69. Stirt JA et al: “Defasciculation” with metocurine prevents succinylcholine-induced increases in intracranial pressure, Anaesthesiology 67:50, 1987.

70. Koenig KL: Rapid-sequence intubation of head trauma patients: prevention of fasciculations with pancuronium versus minidose succinylcholine, Ann Emerg Med 12:929, 1992.

71. Rosen P, Wolfe RE: Therapeutic legends in emergency medicine, J Emerg Med 7:387, 1989.

72. Walls RM: Airway management in the blunt trauma patient: how important is the cervical spine? Can J Surg 35:27, 1992.

73. Hauswald M et al: Cervical spine movement during airway management: cinefluoroscopic appraisal in human cadavers, Am J Emerg Med 9:535, 1991.

74. Criswell JC, Parr MJ, Nolan JP: Emergency airway management in patients with cervical spine injuries, Anaesthesia 49:900, 1994.

75. Hastings RH, Marks JD: Airway management for trauma patients with potential cervical spine injuries, Anesth Analg 73:471, 1991.

76. Watts ADJ et al: Comparison of the Bullard and MacIntosh laryngoscopes for endotracheal intubation of patients with potential cervical spine injury, Anesthesiology 87:1335–1342, 1997.

77. Kennedy FR et al: Incidence of cervical spine injury in patients with gunshot wounds to the head, South Med J 87:621, 1994.

78. Abbott Laboratories: Product insert, Quelicin (succinylcholine chloride injection, USP).

79. Medina FA: Rapid sequence induction/intubation using intraosseous infusion of vecuronium bromide in children, Am J Emerg Med 10:359, 1992.

80. Cohn AI, Zornow MH: Awake endotracheal intubation in patients with cervical spine disease: a comparison of the Bullard laryngoscope and the fiberoptic bronchoscope, Anesth Analg 81:1283, 1995.

81. Cohn AI, McGraw SR, King WH: Awake intubation of the adult trachea using the Bullard laryngoscope, Can J Anaesth 42:246, 1995.

82. Wadbrook P, Pollack CV: Utility of the Bullard laryngoscope for ED trauma intubations, Ann Emerg Med 34:S14, 1999.

83. Brimacombe JR, Berry A: The incidence of aspiration associated with the laryngeal mask airway: a meta-analysis of published literature, J Clin Anesth 7:297, 1995.

84. Samarkandi AH et al: The role of laryngeal mask airway in cardiopulmonary resuscitation, Resuscitation 28:103, 1994.

85. Reinhart DJ, Simmons G: Comparison of placement of the laryngeal mask airway with endotracheal tube by paramedics and respiratory therapists, Ann Emerg Med 24:260, 1994.

86. Baskett PJF: The intubating laryngeal mask: results of a multi-center trial with experience of 500 cases, Anaesthesia 53:1174–1179, 1998.

87. Joo HS, Rose DK: The intubating laryngeal mask airway with and without fiberoptic guidance, Anesth Analg 88:662–666, 1999.

88. Hung OR et al: Clinical trial of a new lightwand device (trachlight) to intubate the trachea, Anesthesiology 83:509–514, 1995.

89. Knight RG et al: Arterial blood pressure and heart rate response to lighted stylet or direct laryngoscopy for endotracheal intubation, Anesthesiology 69:269, 1988.

90. Staudinger T et al: Emergency intubation with the Combitube: comparison with the endotracheal airway, Ann Emerg Med 22:1573, 1993.

91. Vezina D: Complications associated with the use of the esophageal-tracheal Combitube, Can J Anaesth 45:76–80, 1998.

92. McNamara RM: Retrograde intubation of the trachea, Ann Emerg Med 16:680, 1987.

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93. Yealy DM, Stewart RD, Kaplan RM: Myths and pitfalls in emergency translaryngeal ventilation: correcting misimpressions, Ann Emerg Med 17:690, 1988.

94. Walls RM: Cricothyroidotomy, Emerg Med Clin North Am 725–737, 1988.

95. Walls RM, Pollack CV: Successful cricothyrotomy after thrombolytic therapy for acute myocardial infarction: a report of two cases, Ann Emerg Med 35:188–191, 2000.

96. Chan TC et al: Comparison of wire-guided cricothyrotomy versus standard surgical cricothyrotomy technique, J Emerg Med 17:957–962, 1999.

97. Barton ED et al: What is a complication? Classifying events during emergency intubations, Acad Emerg Med 6:365–366, 1999.

[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.

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