Rise in cuff pressure with Nitrous Oxide

[yogenbhatt1]

Hi,
I read a lot about cuff pressure of ETT and LMA going up by 15-20 % in 60 mins of surgery with 66% Nitrous used as gas in any circuit.
I am a bit confused about it. Ofcourse they must have conducted studies and even analysed nitrous presence i n the cuff. Also body temp will also increase the volume of gases in the cuff.
Any second opinion on this?
We have a rule to release and reinflate the cuff after 1 hour because a little tissue edema also takes places and so the cuff fits snuggly leading to no leak on complete deflating also. Is it not a combine effect of gas and edema and temp that the pressure rises?
Or  is it that a lot of nitrous enters the cuff through the PVC or what ever material?

[Marifel12]

As far as I know, nitrous oxide, commonly known as happy gas or laughing gas, is a chemical compound with the chemical formula N2O. Then, is it needed for this cuff pressure? Can I know the reason?


_________________
Indianapolis Plastic Surgery

[yogenbhatt1]

Is Nitrouoxide needed for cuff of endotracheal tube?
Is that the question?
We are discussing, if Nitrous enters the cuff from the tissues.
Does it and can it actually enter? That is the question.
Cuff pressure does rise. But does it rise due to entry of Nitrous in the cuff? Is there an article that says so and chemically proved that cuff contains Nitrous?
That was my question!

[Dr. Mian]

That ETT cuffs take on nitrous when used as an adjunct anesthetic (and hence ETT pressure goes up) was also taught to me during training.  However, I have never found any source which supports this view and the mechanism was never explained to me satisfactorily.

Of course N20 replaces air in enclosed spaces such as bowel, middle ear cavity although again the mechanism was never explained to me satisfactorily.  However, I can not imagine that the same process takes place in an ETT cuff which must be nonpermeable to gases or else how would it ever retain the air in the first place

[jafo1964]

My understanding of the subject

All materials absorb gases in varying concentrations

So Nitrous Oxide has been found to permeate across the thin PVC sheet that forms the cuff. That explains that N2O can move around
In fact various rubber and plastic tubings can absorb varying quantities of inhalational agents as gases
This uptake by circuit needs to be factored in when practising low flow anaesthesia techniques
These taken up gases by circuit may be relaesed later and can theorotically delay recovery
SO N2O can move across the thin PVC cuff

If there is a semipermeable membrane gas molecules move across it based on concentration gradient from high to low concentration. That simply explains how CO2 is given into lungs and O2 taken up at lungs. Lungs have less CO2 and more O2 compared to venous blood. The vice versa happens at the tissue level
Obviously the cuff is filled with air ( no N2O) while the inspired gas has 66% of N2O so obviously N2O will move in according to the concentration gradient. and it will continue to move until equilibrium is acheived across the membrane . Meaning inside the ETT cuff too there must be 66% N2O to prevent further movement.
There is another additinal problem. N2O is almost 30 times more diffusible than other gases. So in the time taken for 1 air molecule to move out nearly 30 N2O molecules can move in . So N2O fills in faster than air moves out( SIMILAR OCCURENCE DURING FINK EFFECT / DIFFUSION HYPOXIA). If this change occurs in a compliant space like air in intestines, then the intestines bloat as during laprotomy.
IF N2O moves into non-compliant spaes like middle ear or ETT cuff the volume cannot expand much so the pressure increases producing the damages

In ETT cuff N2O moves in faster than air moves out leads to increase in presure above the safe  allowed 18 mm Hg and can compromise tracheal mucosal blood flow
So you need to check pressure if you use N2O and deflate and make adjustments in volume as necessary

ALTERNATIVES
Fill cuff with saline or any liquid
Use Inspiratory gas mixture( 66% N2O and 33% O2) to fill cuff
Use manometer to measure and adjust pressure
Use self regulating ETT cuff systems like Lanz system or Mcginnis cuff balloon system

Hope this explanation is decipherable and
Hope to God this is the correct explanation for this oft ignored phenomenon

regs

[peeciss]

@ jafo: good answer  :D

personally, we use a manometer attached to the ETT or LMA and mostly 50% N20 in inhalation anaesthesia and the cuff does inflate :)

[kalpesh shah]

hi, can we get more information about macinninz ballon system and lanze system tubes...
   

thank you.

[huafeihua116]

My understanding of the subject

All materials absorb gases in varying concentrations

So Nitrous Oxide has been found to permeate across the thin PVC sheet that forms the cuff. That explains that N2O can move around
In fact various rubber and plastic tubings can absorb varying quantities of inhalational agents as gases
This uptake by circuit needs to be factored in when practising low flow anaesthesia techniques
These taken up gases by circuit may be relaesed later and can theorotically delay recovery
SO N2O can move across the thin PVC cuff

If there is a semipermeable membrane gas molecules move across it based on concentration gradient from high to low concentration. That simply explains how CO2 is given into lungs and O2 taken up at lungs. Lungs have less CO2 and more O2 compared to venous blood. The vice versa happens at the tissue level
Obviously the cuff is filled with air ( no N2O) while the inspired gas has 66% of N2O so obviously N2O will move in according to the concentration gradient. and it will continue to move until equilibrium is acheived across the membrane . Meaning inside the ETT cuff too there must be 66% N2O to prevent further movement.
There is another additinal problem. N2O is almost 30 times more diffusible than other gases. So in the time taken for 1 air molecule to move out nearly 30 N2O molecules can move in . So N2O fills in faster than air moves out( SIMILAR OCCURENCE DURING FINK EFFECT / DIFFUSION HYPOXIA). If this change occurs in a compliant space like air in intestines, then the intestines bloat as during laprotomy.
IF N2O moves into non-compliant spaes like middle ear or ETT cuff the volume cannot expand much so the pressure increases producing the damages

In ETT cuff N2O moves in faster than air moves out leads to increase in presure above the safe  allowed 18 mm Hg and can compromise tracheal mucosal blood flow
So you need to check pressure if you use N2O and deflate and make adjustments in volume as necessary

ALTERNATIVES
Fill cuff with saline or any liquid
Use Inspiratory gas mixture( 66% N2O and 33% O2) to fill cuff
Use manometer to measure and adjust pressure
Use self regulating ETT cuff systems like Lanz system or Mcginnis cuff balloon system

Hope this explanation is decipherable and
Hope to God this is the correct explanation for this oft ignored phenomenon

regs

Great!! :)