Nitrogen Wash Out

SRNA312 · Oct 24, 2006

The pillow doesn't have anything to do with the nitrogen washout. That is for obtaining a "sniffing" position that aligns the oral, pharyngeal, and laryngeal axis in an anatomically optimal manner to ease intubation. Whether you leave the pillow or not is strictly a preference of the endoscopist. Nitrogen washout, also referred to as pre-oxygenation or denitrogenation, is for maximizing the time you have to intubate. As you know, the air you breathe is 21% O2 and 78-79% Nitrogen, 1% other gases. With that being said, at the end of a normal expiration, each person still has more air they can forcefully expire.........this is the expiratory reserve volume (avg =1100cc). Even when you have seemingly blown all the air from your lungs, there is still air in there or they would collapse. This is the residual volume (avg=1200cc). These two volumes together = the Functional Residual Capacity (or FRC). The average FRC is all together is about 2300cc or so give or take, depening on the size, sex, and sicknesses of the patient. Out of that 2300cc, at least 78% of it is Nitrogen. The goal of denitrogenation is to make the FRC be 100% O2. This is done with 3-5 minutes of breathing 100% O2 (there HAS to be a good seal.....no entrained room air allowed!) or sometimes people do it with 4 vital capacity breaths of 100% O2. Depending on what book you read, the avg human consumes O2 at a rate of about 250cc/min. If your FRC is 2300cc, then if it was filled with 100% O2, that would give you about (2300/250=) 9 minutes or so before the patient would desaturate. That would be for a healthy person.Now you must understand that "sick" people usually consume O2 at a lot faster pace so you wouldn't have as much time to intubate but just understand that denitrogenation is to buy you time and the above is a detailed explanation as to how it buys you time. I have seen dentritrogenated patients maintain a 100% saturation for what seems like an eternity with absolutely no ventilation at all.

deepz · Oct 24, 2006

........I have seen dentritrogenated patients maintain a 100% saturation for what seems like an eternity with absolutely no ventilation at all.

Pretty fair explanation ... BUT ... don't be misled that all is well simply on the basis of a good sPO2, if one then disregards what happens with a rapidly escalating pCO2 and the deleterious effects that accompany hypercarbia. Separate mechanism, commonly not appreciated.

Good air in, bad air out. It ain't all that hard.

deepz

SRNA312 · Oct 24, 2006

Very true and very good point. Other things are definitely happening. If, during a difficult intubation or whatever, your denitrogenated patient with 100% sats hasn't had a breath in a bit, you may want to consider giving breaths, if for nothing else, to blow off C02.

**canoehead, BSN, RN** · Oct 24, 2006

Thank you, that sounds like something nursing could assist in by putting the pt on NRB a few minutes before we are ready to intubate.

catcolalex · Oct 25, 2006

I would think that if the pt needs to be intubated, that they already have at least a non-rebreather on?

dfk, RN, CRNA · Oct 26, 2006

Thank you, that sounds like something nursing could assist in by putting the pt on NRB a few minutes before we are ready to intubate.

just remember, too, that a NRB retains CO2.. so not the most optimal choice in every situation.. COPDers, it's good.. perhaps a venti or plain O2 mask would be just fine

**canoehead, BSN, RN** · Oct 26, 2006

I would think that if the pt needs to be intubated, that they already have at least a non-rebreather on?

Yeah, I would think too, but apparently not- hence the inservice.

Last night we had a 400lb man with no neck, and very edematous CHF come in with almost no air entry. Attempted BiPAP but the straps on the masks didn't fit because he was too big. Rapid sequence intubation- the ER doc and one of our most experienced EMT's attempted intubation unsuccessfully. Respiratory was called in at that point, and anesthesia. We are a small hospital so both were about 30 minutes away. Let the man wake, but he was still unable to move air and he was fighting us so put him down again and bagged. His belly got double in size and tight as an almost bursting basketball. NGT was passed x3 without success. LMA sizes 4 and 5 were both too small to prevent air leakage and sats dropped with those attempts. We didn't cric because the doc felt the landmarks were invisible (and we do those like, once a century). Anesthesia came in and attempted all of the above, but we ended up transporting him (30 minute ride) with bag-valve mask to a higher level facility where ENT trached him.

Suggestions on alternatives that might have worked for the next time this happens? I totally HATE not having an airway- we spent 2 hours. pH7.04 and PCO2 162 when he left- he seemed to be exhaling into his belly! Sats stayed in the low 90's with bagging so I certainly got a demonstration of how the SpO2 can be misleading that night.

deepz · Oct 26, 2006

....... 400lb man with no neck........LMA sizes 4 and 5 were both too small to prevent air leakage and sats dropped with those attempts.

No size 6 available? Actually I don't get too excited about air leakage at first -- if Spo2 and EtCO2 are acceptable; LMAs seem to seat much better in a short time as a patient relaxes more with deeper anesthesia. (LMA literature used to list the first cause of air leakage as Excessive Bagging.)

.....pH7.04 and PCO2 162 ....... Sats stayed in the low 90's with bagging so I certainly got a demonstration of how the SpO2 can be misleading that night.

What a nightmare. Good luck with your inservice!

deepz

**canoehead, BSN, RN** · Oct 26, 2006

Oh, I forgot to ask...our CO2 detector turned color confirming ETT placement, but the ETT was definitely in the esophagus per breath sounds and dropping sats. How much can we rely on the CO2 detector alone- not at all? If so then what is the point of using it?

ECMOismygame · Oct 26, 2006

just remember, too, that a NRB retains CO2.. so not the most optimal choice in every situation.. COPDers, it's good.. perhaps a venti or plain O2 mask would be just fine

partial non-rebreathers retain CO2. non-rebreathers have a valve that will not allow CO2 to be rebreathed.

rn29306 · Oct 26, 2006

Not that I was there, so don't kill the messenger.

I've intubated several 400 'pounders using the Glidescope right off the bat, one of them was a post-op carotid rebleed. I felt in those couple certain circumstances that performing DL would have been just about impossible for anyone to get a straight visual to the cords. The amount of tissue was uttlerly amazing, esp the tongue and depth to the cords.

I had a CRNA while I was in school tell me...."Son, do ya think they are gonna be skinny on the inside or something?"

While fiber optic would probably have been pretty much useless at this point considering the intubation attempts (and at times like these, you have to be rather forceful) the GS would have been great. Do you guys have a difficult airway cart? If so, consider an intubating LMA...Even if you can't get the best seal for a few minutes, throw a tube down it ASAP.

People complain about the price of a GS...but if this man had a hypoxic injury, the 10-14K would have been chump change compared to everyone's payout.

Sounds like you guys had a horrible situation and you handled it to the best of your ability. Think about having anesthesia set up a difficult airway cart, either on your floor or you having access to it while they are coming in for something like this next time. Great job!