I am new to these boards but I have been reading them for several months. I am a paramedic taking prereqs towards a BSN so I can eventually become (surprise) a CRNA.
I'm sure I will be asking everyone multiple questions about the profession and everything else you can imagine but this one is about ET tube placement: Paramedics, as you probably know, usually tube the pt while he is on the floor and then move him to a long spine board (if we transport). How much movement of the tube, would you say, does it take for it to be dislodged? I've heard it takes no more than a few millimeters. Is there any trick to moving a pt to avoid displacement (as when CRNAs move a pt to prone position for back surgery)?
If I am following this thread correctly, some are stating that CRNAs in the past have cut excess tube length from an OETT in an effort to decrease airway resistance.
One has to assume several things, esp when dealing with the theory of physics involved in anesthesia. Assume that you have laminar flow inside the OETT (nevermind that 90 degree connector at the end of the OETT).
Laminar flow follows Poiseuille's law of R = 8nl/r^4
R = resistance
n = viscosity
l = length
r = raduis
By applying the forumla and examining it, you can see that length of the OETT is directly proportional to airway resistance. So cutting excess length from an OETT will decrease airway resistance to a certain degree. Further examination shows that a much greater variable to airway resistance is not length, but radius, specifically the FOURTH power of the radius. While length and airway resistance are directly related, the radius and resistance are inversely related.
The take home point is that if you double the radius, your airway resistance drops by a factor of 16 (2^4).
This is why some institutions place a #9 in adult males and #8 in females for cardio and thoracic surgeries, in order to maximize this concept and allow for as stress and resistance free wean / extubation as possible.
all of which i understand are nothing compared to increasing radius...however - those were his reasons.
athomas, how much was he cutting off?
i am no one to second guess anyone, not you or the crna, so don't take this as a personal attack, but you were there and saw it happen and have a better opinion about it than i do.
what is your opinion of the above practice?
just how much airway resistance do you think a person can lose by doing this?
did you see your peak ventilating pressures drop significantly?
just how much dead space did it appear you lost by the CRNA doing this?
. Further examiniation shows that a much greater variable to airway resistance is not length, but radius, specifically the FOURTH power of the radius. While length and airway resistance are directly related, the radius and resistance are inversely related.
The take home point is that if you double the radius, your airway resistance drops by a factor of 16 (2^4).
This is why some institutions place a #9 in adult males and #8 in females for cardio and thoracic surgeries, in order to maximize this concept and allow for as stress and resistance free wean / extubation as possible.
I always encourage the SRNAs in my institution to increase the size of their ETTs when doing a longer case and on larger people. Most use 7s on women and 7.5 on men. I remember being told of a study that had med students (lol, of course who else?) being intubated with differing sizes of ETT and told to breath normally. The one's with the smaller tubes tired out very quickly. I talk about Pouseille's law and why increasing the radius is very important to decreasing the resistance that the patient has to work against. I ask my students to put themselves in the place of the patient, waking up from anesthesia, and having a larger tube. This makes it easier to breath, and is much nicer for the patient IMHO. I don't see many complain of sorer throats with larger tubes.
Looking at the math (which gave me a headache!) it seems to me that the practice of shortening a tube in regards to the effects of Poiseuille's law would be negligible. What patient would you have that such a small change would benefit?
Looking at the math (which gave me a headache!) it seems to me that the practice of shortening a tube in regards to the effects of Poiseuille's law would be negligible. What patient would you have that such a small change would benefit?
That is my point exactly. Honestly, how many mls of dead space are you eliminating by cutting off two cm of tube? Maybe 5?
You have about 4-5 feet of circuit tubing, multiple valves and connectors, and some people are cutting several centimeters of OETT tubing to "decrease deadspace". I for one just don't see it.
Then you get into situations like the burn RN noted and all of a sudden, your tube is doing a disappearing act and you have to change it out over a FOB if you are lucky. What I don't see is the point of eliminating a few mls of dead space. Why not just turn up your ventilating volume?
rn29306
533 Posts
You may gain a miniscule amount of decrease in resistance, but this practice, esp for burn patients is laughable at best.