Apneic Oxygenation

[Carlos Danger]

Is anyone aware of any literature that shows improved outcomes in difficult airways when apneic oxygenation is used?

Weingart and Levitan make a good case for it here, and while they list plenty of supporting references in table E1, none of those studies look specifically at patients who were expected or found to have difficult airways. In fact, the only one of the studies listed that I thought might do so based on the description was the one by Ramachandran et al, yet they actually excluded C&L 3/4 patients......the very ones in whom extending safe apneic time would be valuable.

So, while the ability of apneic oxygenation has been well established to extend oxygenation times in healthy patients, I question whether it actually makes a difference in the sick / difficult airway population.

 

[lightsandsirens5]

What do you mean by sick/difficult airway patient? Do you mean anatomically difficult, or difficult because of...shall we say...time constraints. Do you not expect it to make a difference in someone who desaturates more quickly?

I have not come across any literature looking at apneic oxygenation in difficult airways, though I too would be interested to see it. I would also like to see a study on apneic oxygenation specifically in right shifted patients, or others that have difficulty maintaining an adequate saturation, or who have a less than desirable sat going into the RSI.

 

[Carlos Danger]

What do you mean by sick/difficult airway patient? Do you mean anatomically difficult, or difficult because of...shall we say...time constraints.

Both. Difficult for either anatomic or physiologic reasons, but I guess I am thinking more about the physiologically difficult airway.

Do you not expect it to make a difference in someone who desaturates more quickly?

Not necessarily. In a healthy person, the response to apnea is quite predictable and the studies show safe apneic time is extended significantly with apneic oxygenation. However, if someone desaturates quickly, then that is probably because they have some pathology which increases oxygen requirements.

So if someone's oxygen demand is really jacked up (a severe shock state) and their FRC is low, does mass flow from the pharynx supply enough oxygen to make a difference?

What about the patient who has severe OSA - would the oxygen even be able to flow into the glottis? I wouldn't think so. I also wouldn't expect it work very well in anyone with a significant A-a gradient or in someone with atelectasis or a high closing capacity who relies on volume to keep their small airways open.

My point is that I can think of reasons why this might not work well in the very patients we need it to work well in - those who desaturate quickly - and I've not seen any research to the contrary. I'm looking for a reason to believe in this technique and to incorporate it into my practice.

 

[lightsandsirens5]

Oh I agree with you completely.

I think there are some cases where it would improve the whole situation, and some where it would not. I doubt it would hurt. (And no I am not advocating a "let's do it because it can't hurt" mindset.) I just think it would completely depend on, among other things, the underlying pathology and any associated comorbidities, if you will.

I think it would have minimal effect in those patients where you have mere seconds to get them tubed after stopping ventilation.

Anyhow...if you do run across any studies, let me know. I am curious now...hmmm...research project for on shift tomorrow...

 

[medicsb]

I don't think there is anything to show that this actually reduces M&M. It could be pretty easily studied via a double blind RCT (one could easily mask cylinders so one cannot tell if the patient is receiving "medical" air or oxygen). However, I imagine that IRBs in the US wouldn't allow this sort of thing.

Halothane makes good points about the sickest patient likely not benefiting from it nearly as much as healthier patients. However, a gain of even 20 seconds could be beneficial to the sick patients. Overall, I see few downsides, though one big downside could be a false sense of security leading to poor planning for a precipitous desaturation.

 

[Brandon O]

I don't think there is anything to show that this actually reduces M&M. It could be pretty easily studied via a double blind RCT (one could easily mask cylinders so one cannot tell if the patient is receiving "medical" air or oxygen). However, I imagine that IRBs in the US wouldn't allow this sort of thing.

Why do you think it'd be hard to get approval? Seems like a pretty benign intervention. Although nobody's going to pay for it, so it might take some doing to get the numbers you'd need.

Halothane makes good points about the sickest patient likely not benefiting from it nearly as much as healthier patients. However, a gain of even 20 seconds could be beneficial to the sick patients.

Agreed on both fronts. You'd expect sick folks to achieve less benefit than the magit that's been demonstrated in the small proof-of-concept studies on healthy folks, but those are also the patients for whom a few seconds is worth the candle.

 

[medicsb]

Why do you think it'd be hard to get approval? Seems like a pretty benign intervention. Although nobody's going to pay for it, so it might take some doing to get the numbers you'd need.

Yeah, I might have been a little too pessimistic.

 

[blindsideflank]

This is a good example where I think evidence based medicine is overly appreciated. The physiology is sound and that satisfies me enough to use this whenever possible. With all the variables of different systems, underreporting (hypoxic episodes during intubation), skill levels etc. I would have little trust in a study on this anyways.

The charts are so strong in healthy patients that I believe this should be a standard. It is now in my service.

 

[Carlos Danger]

This is a good example where I think evidence based medicine is overly appreciated. The physiology is sound and that satisfies me enough to use this whenever possible. With all the variables of different systems, underreporting (hypoxic episodes during intubation), skill levels etc. I would have little trust in a study on this anyways.

The charts are so strong in healthy patients that I believe this should be a standard. It is now in my service.

Well, you can't assume that just because something works for healthy patients then it will be helpful in sick patients. The way a sick patient responds to apnea is very different than the way a healthy person does.

The thing is, anyone I can mask effectively is not a "difficult airway". So basically, if I can easily keeps someone's sats up by masking them, I have little need for a technique like this. The problem is, the factors that make it difficult to keep sats up while masking are the same factors that would likely preclude this technique from helping much. That's the whole hitch right there.

I suppose you can take the approach that "well, it isn't going to hurt, and it just might help a little, so let's just do it", but personally I think that's a poor rationale to base a practice on. That's exactly how we got long spine boards and NRB's for everyone, as well as MAST pants, helicopters on every street corner, driving code everywhere, and intracardiac epi and first-line bicarb. One could write a book listing the practices that came about using that thinking that we now laugh at. So for one thing, we don't know for sure that it never hurts (a NC could make it harder to get a good mask seal), and also it assumes that you have good reason to think it helpful in the first place, but unfortunately I've yet to find a study or a CRNA or an MDA that agrees that it does.

I have very little faith in research performed in the EMS setting as well. The best place by far to study this would be in an ED that gets lots of really sick patients, and preferably where the intubations are done by EM attendings or anesthesia, so that variations in the skill of the intubator is less of a factor.

 

[Brandon O]

The thing is, anyone I can mask effectively is not a "difficult airway". So basically, if I can easily keeps someone's sats up by masking them, I have little need for a technique like this.

Not quite sure if I'd agree with that. You can have someone who you're able to ventilate with a mask but who's a very difficult tube. That's a million times better than if you couldn't bag them, of course, but it still leaves you stuck, unless you're planning on BVMing them for the next two weeks...

 

[Carlos Danger]

Not quite sure if I'd agree with that. You can have someone who you're able to ventilate with a mask but who's a very difficult tube. That's a million times better than if you couldn't bag them, of course, but it still leaves you stuck, unless you're planning on BVMing them for the next two weeks...

Well, I don't think you are ever really "stuck" if you can effectively mask, because you always have that as a perfectly viable management option. If you've failed a couple of ETI attempts but you can mask well, you have plenty of time to come up with an alternative plan and prepare for it, whether that's a cric, a retrograde, or an LMA. Or maybe you just let them recover from the sux and breath on their own in a recovery position. Or maybe you mask them the entire transport. Or you have someone else come and help, maybe have them bring the FOI equipment if it's available. No matter what else is going on or what you are having difficulty with, the patient is never in trouble if you can mask them well. No patient has ever died from lack of intubation.

But the more pertinent point was that if I can't mask someone, then I would't expect passive oxygenation to work, because whatever is obstructing my positive pressure ventilations (blood, tissue if they are obese, etc.) would surely obstruct the passive oxygenation as well.

There are those cases where the airway is completely open and strictly external factors (thick beard) make masking difficult, though.

 

[Brandon O]

There are those cases where the airway is completely open and strictly external factors (thick beard) make masking difficult, though.

Right. There's plenty of overlap between the factors that challenge intubation and ventilation, but also lots of unique problems to each. I would guess (no data on hand for this) that the most common obstacle to the BVM is poor mask seal, and the most common for intubation is challenging anatomy. Those don't have to go together.

For the most part, I agree with you. Just trying to say that even if you can BVM someone, if they keep desatting whenever you try to tube them, there's real value in "one weird trick" that gives you additional time to fish. I grant this is less of an issue in the field, where in many cases you can legitimately decide to just bag them all the way in -- but at some point in the course of care, somebody's gonna need to transition away from that.

But you're right that it'll probably provide less oxygenated time in the real world than in healthy volunteers.