Doesn't the intubation pipe itself blocks some of the air?

[Good Samaritan]

Hi everyone,

I'm not a medical student, I just read about intubation and saw this picture on wiki

I got curious.

The intubation is partially meant to clear the airway from all sorts of fluids/goo/junk, but in the process it blocks some of the air itself due to the width of the pipe walls, right?

[chbare]

It typically has a smaller diameter/radius than the airway and will add resistance to the flow of air. This can increase the work of breathing. In fluid dynamics this is explained by something known as Poiseuille's law. However, Poiseuille's law in it's standard form assumes incompressible fluid and laminar flow, so it's only a gross approximation when using compressible fluid and turbulent flow. The tube may also increase something known as deadspace, mechanical deadspace to be specific.

Take care,

chbare.

[tniuqs]

Short answer YES.

Almost a mute point but ETI will actually decrease physiological deadspace, if one looks comparably at the volume in the upper airway, it quite easy to observe that the "volume contained in the ETT" itself is markedly less. This can effect End Tidal CO2 readings/levels but minimally, when ventilating and taking away WOB (the intent of ETI) the "mechanical" deadspace becomes more of a factor as the circuits used generally add more deadspace, an artificial nose or "humidivent" "bacterial filters" also increases mechanical deadspace (the portion of a tidal volume "i.e. a single breath" that does not undergo alveolar gas exchange) spacers for medications or tape flex additions also add Vd/Vt.

I don't think getting into "effective" MV vs "set" MV discussions and loss of volume to tubing compliance is or of value at this juncture, but should be mentioned in passing as "a couple years of Lung School" is essential to clearly understand pulmonary mechanics, as well as years of experience to put these concepts into actual practice.

Good Samaritan:

Your observation of "goo/secretions" and increasing resistance to airflow is most excellent and reflected on a gauge called "Peak Inspiratory Pressure" (IMHO they should have one in-line on ALL Manuel Resuscitators as well in EMS to prevent inadvertent "overpressure")

This number is measured on a ventilator moreover a very serious complication in longer term ventilation or with pneumonias (due to the increased volume of secretion production) The ETT is guide for a suction catheter to remove said "goo" in the spontaneously breathing patient the "cough" is the mechanism to eliminate the goo, well until the patient "craps out" and fails. Yet again you are correct if one was just breathing though a "straw" on their own .. this would add an increased WOB or work of breathing. .. Try it to see for yourself in ten minutes it becomes very apparent.

chbare brings up a good physics point with Poiseuille's Law .. A clinical bedside formula I use teaching Paramedics is that if one decreases an inner diameter by half this increases resistance to flow 16 TIMES .. so not to be taken lightly especially when using one "mode" of ventilation called Pressure Control, best left for pros to use.

Another "rule of thumb" I use is that with set average flows set on a transport ventilator are 40 to 60 cm H20 per liter per second, so with an "average" resistance with a # 8 mm tube your looking on the Peak Pressure Gauge of a factor of 8 cmH20, even before looking at overcoming the resistance, compliance and elastic recoil of the chest wall.

Yes its eyeball but when setting up a Ventilator on a patient the resultant sequelea of ARDS (adult respiratory distress syndrome) and adverse effects of barotrauma are of very serious concern's especially longer term for survival of those committed to Life Support.

cheers

Edited July 16, 2011 by tniuqs

[chbare]

I was thinking about the circuit attached to the tube and related equipment (cascade) that would go along with the tube relating to mechanical deadspace, but probably a moot point as stated.

Take care,

chbare.

[tniuqs]

I was thinking about the circuit attached to the tube and related equipment (cascade) that would go along with the tube relating to mechanical deadspace, but probably a moot point as stated.

Take care,

chbare.

I think a excellent start for Good Sam in observation alone and great question for first post .. the point of resistance allows for a teaching point both in secretions and affecting pressures when squeezing a BVM, the hows and whys of the pressures are generated.

Maybe a bio person that we can recruit to the dark side of Respiratory Therapy ? Pulmonary Mechanics is really not dealt with in the detail that it should in EMS especially the negative pressure effects on the heart.

[Good Samaritan]

Thanks or the feedback, chbare, tniuqs! I didn't expect so much excellent details, but am happy to have that. I am already getting the feeling this is an incredible forum to learn a lot from emergency medical professionals. What a gem!

You've used plenty of slang and a lot of scientific explanation that I sat through reading trying to decipher. I used this:

http://www.suslik.org/Humour/FirstAid/acronyms.html

But I couldn't understand what WOB means so I was beginning to lose parts of the string.

But I'm glad to know my logic proved true, and that is certainly an interesting fact about Poiseuille's Law. But I guess the advances in Intubation override the little harm it does, or you wouldn't use it.

Thank you!

-GS

[tniuqs]

Thanks or the feedback, chbare, tniuqs! I didn't expect so much excellent details, but am happy to have that. I am already getting the feeling this is an incredible forum to learn a lot from emergency medical professionals. What a gem!

You've used plenty of slang and a lot of scientific explanation that I sat through reading trying to decipher. I used this:

http://www.suslik.org/Humour/FirstAid/acronyms.html

But I couldn't understand what WOB means so I was beginning to lose parts of the string.

But I'm glad to know my logic proved true, and that is certainly an interesting fact about Poiseuille's Law. But I guess the advances in Intubation override the little harm it does, or you wouldn't use it.

Thank you!

-GS

Actually there is no slang used only accepted medical acronyms and the "advances in Intubation" that you refer there are many serious and life threatening complications that arise from committing an Individual to Life Support, never to be taken lightly.

perhaps you missed this .. this would add an increased WOB or work of breathing. .

But the link to the acronyms that one should NOT use on a PCR ... most worth while.

[Good Samaritan]

Sorry, I meant advatnages of intubation, and yes -- I meant acronym not slang. You're alright

Thanks! In all all very informative.

-GS