NC or NRB when suction is needed?

[mycrofft]

Have to wake them up first probably.

 

[mycrofft]

OP, had enough?

( Sent Email off to Dr Levitan's website. )

80% of the OP's answer was in the first response I think. There is a remaining 20% is polishing the other 80%, but it is important.

1. Is the nose patent for NC oxygen?

2. Is the flow meter correct? (Right variety for the delivery device; no obstructions to fudge the results of a Bourdon or preset flow regular/gauge; if Pitot, is it virtually vertical?).

3. Have you assumed responsibility for the pt's airway by strapping them onto a board or drugging them, or is there even a real need to suction at this point? (Not bad to be ready though).

 

[Brandon O]

( Sent Email off to Dr Levitan's website. )

Not exactly this topic, but I have asked Dr. Weingart whether there's evidence for their recommendation of 15 LPM for preox/apneic oxygenation, and although there's data for the general principle, that specific number seems to just be a best-guess.

Apneic oxygenation, however, is probably a different issue than spontaneous respirations anyway, since it's a different method of gas flow and insufflation (mass movement by diffusion gradient rather than an active bellows).

 

[Carlos Danger]

Not exactly this topic, but I have asked Dr. Weingart whether there's evidence for their recommendation of 15 LPM for preox/apneic oxygenation, and although there's data for the general principle, that specific number seems to just be a best-guess.

Apneic oxygenation, however, is probably a different issue than spontaneous respirations anyway, since it's a different method of gas flow and insufflation (mass movement by diffusion gradient rather than an active bellows).

Good points. I've been skeptical of the application of apneic oxygenation in airway management and have also been unable to find evidence in support of it. I have a suspicion that it works much better in non-difficult airways than in difficult ones.

I too am curious about the mechanics of oxygen delivery at high flow rates (say, > 6 lpm) via a non-high flow NC vs. a high-flow one. How does it work? Does it result in better oxygenation that a lower flow rate would? Is it as good a a HFNC? Etc.

 

[mycrofft]

Dr Levitan's website does not reply.

 

[Carlos Danger]

Dr Levitan's website does not reply.

What was the question?

 

[ThadeusJ]

As an aside for apneic oxygenation, when assessing brain death in the hospital, one of the tools is an apnea test. In this test, you remove mechanical ventilation and perform a series of ABG's to see the rise in PCO2 (obviously if there are registered breaths during the test, the patient is not apneic). In order to maintain proper oxygenation, a suction catheter is placed down the ETT to the tip of the carina and 6 LPM oxygen is piped through it. Oxygenation must be maintained throughout the test or else the test is stopped.

Therefore, the body will absorb oxygen passively while PCO2 builds from apnea. It is interesting to see.

Here's a link:
https://www.aan.com/Guidelines/home/GetGuidelineContent/433

 

[mycrofft]

What was the question?

I forget...:huh:

Oh, yeah. The Levitan material says give 15 lpm via nasal cannula but nowhere does it say if that is via special high flow NC or standard or "traditional" NC. I pointed this out and asked if it was understood it was special NC. They didn't answer.

 

[Brandon O]

As I understand it they're referring to a standard NC. This is ED-type airway management stuff.

 

[Carlos Danger]

I forget...:huh:

Oh, yeah. The Levitan material says give 15 lpm via nasal cannula but nowhere does it say if that is via special high flow NC or standard or "traditional" NC. I pointed this out and asked if it was understood it was special NC. They didn't answer.

Did you read the paper that Levitan and Weingart jointly authored on this subject? They state that a "normal" NC should work fine. Weingart has also made that claim on his podcasts.

From page 6 of the paper:

To provide apneic oxygenation during ED tracheal intubations, the nasal cannula is the device of choice. Nasal cannulas provide limited FiO2 to a spontaneously breathing patient, but the decreased oxygen demands of the apneic state will allow this device to fill the pharynx with a high level of FiO2 gas. By increasing the flow rate to 15 L/minute, near 100% FiO2 can be obtained. Although providing high flow rates with a conventional, nonhumidified nasal cannula can be uncomfortable because of its desiccating effect on the nasopharynx, after the patient has been sedated it should cause no deleterious effects for the short interval of airway management. Tailor-made high-flow nasal cannulas are also available that will humidify the oxygen, allowing flow rates up to 40 L/minute.

As I said before, I'm highly skeptical of the utility of the practice. There is plenty of evidence that apneic oxygenation through an NC works, just none that I've ever seen that shows it extends safe apneic time in the difficult airway patient, where airway obstruction (preventing mass flow) is a defining feature.

 

[Brandon O]

As I said before, I'm highly skeptical of the utility of the practice. There is plenty of evidence that apneic oxygenation through an NC works, just none that I've ever seen that shows it extends safe apneic time in the difficult airway patient, where airway obstruction (preventing mass flow) is a defining feature.

I'm sure nobody would think it's effective in a complete airway blockage (e.g. laryngospasm), but that's not usually what we're dealing with in a "difficult airway." If there's literally no free passage from world to alveoli, I hope anybody who can do math realizes you don't have many options except cric.

 

[Carlos Danger]

I'm sure nobody would think it's effective in a complete airway blockage (e.g. laryngospasm), but that's not usually what we're dealing with in a "difficult airway." If there's literally no free passage from world to alveoli, I hope anybody who can do math realizes you don't have many options except cric.

Well I would hope you are right about that, but I'm not talking about complete airway blockages, anyway.

How often have you seen effective mask ventilation outside the OR? I'd guesstimate about half the time, maybe less. Usually when it isn't working it's because of soft tissue obstruction of the upper airway due to poor positioning. So here's the thing: if you can't get oxygen to pass through the airways under positive pressure, you surely aren't going to get it in via mass flow and passive diffusion. Not to mention the fact that the ability to mask ventilate obviates the need for passive oxygenation, anyway. The airways that you really need apneic oxygenation to work on are exactly the ones that the technique is the least likely to work on.

I'm not saying it shouldn't be done or that it would never be helpful, I'm saying I don't think it makes a very good safety net for the difficult airway.

 

[Brandon O]

How often have you seen effective mask ventilation outside the OR? I'd guesstimate about half the time, maybe less. Usually when it isn't working it's because of soft tissue obstruction of the upper airway due to poor positioning.

I think that's too strong of a claim. Sometimes the airway is totally blocked (often, as you say, due to inadequate positioning). But it may only be narrowed, which makes things difficult, particularly if it tends to favor airflow down the esophagus. Or it may be transiently difficult (as in, you're not locked into a solid setup that you can reliably bag into, but as you move them around you keep opening and closing the airway), which would allow intermittent passive flow. And many times the challenges are merely due to mask seal.

Filling the pharynx with passively-insufflated oxygen is a safety net. You shouldn't be relying on it, and you should be doing your best not to need it. But it takes little time and has negligible harms, and may help "cover your mistakes" when you're not perfect, which is exactly the sort of thing that's helpful for building a layered approach -- you want stuff you don't have to think about behind the stuff you're actively working on.

 

[mycrofft]

Did you read the paper that Levitan and Weingart jointly authored on this subject? They state that a "normal" NC should work fine. Weingart has also made that claim on his podcasts.

From page 6 of the paper:



As I said before, I'm highly skeptical of the utility of the practice. There is plenty of evidence that apneic oxygenation through an NC works, just none that I've ever seen that shows it extends safe apneic time in the difficult airway patient, where airway obstruction (preventing mass flow) is a defining feature.

I've cited sources stating 15 lpm through a device designed not to deliver that amount will not do it by simply turning it up* due to disruption of laminar flow, and noted that Bourdon and fixed flow rate regulators will give you an erroneous reading due to the Bourdons' tendency to overrate flow if pressure climbs (as in blockage) and the regs with little numbers and detents on them which are pre calibrated to an open airway and the designed device being on the end of a reasonable length of hose. Yes you can probably push more through but it won't be "fifteen" unless your pitot (little ball in the column) says fifteen. In the case, gauges can lie.

That said, flooding the naso-oropharynx with oxygen works if/when it is pumped down the airway or the pt inspires; filling this potential dead space with O2 is overcoming seal issues etc with masks alone. I cannot believe flooding the naso-oropharynx with oxygen then just leaving it there (total apnea and blocked airway) will diffuse any appreciable oxygen into the pt, as some folks replying here seem to maybe think. A blocked nose will deny that avenue to feed in naso-oropharyngeal oxygen.

The healthy lung's lining, if microscopically flattened out, has an absorptive surface area approaching that of a tennis court; the oropharynx, that of a medium sized bandana if that, and it is not specifically designed for gas exchange. Reference is made at some points to setting up a high flow NC then putting the respirator mask over it.



* I call this the Spinal Tap Phenomenon.

 

[Brandon O]

That said, flooding the naso-oropharynx with oxygen works if/when it is pumped down the airway or the pt inspires; filling this potential dead space with O2 is overcoming seal issues etc with masks alone. I cannot believe flooding the naso-oropharynx with oxygen then just leaving it there (total apnea and blocked airway) will diffuse any appreciable oxygen into the pt, as some folks replying here seem to maybe think. A blocked nose will deny that avenue to feed in naso-oropharyngeal oxygen.

The healthy lung's lining, if microscopically flattened out, has an absorptive surface area approaching that of a tennis court; the oropharynx, that of a medium sized bandana if that, and it is not specifically designed for gas exchange. Reference is made at some points to setting up a high flow NC then putting the respirator mask over it.

The physiology here is not that the patient absorbs oxygen through the pharynx.

It's more along these lines:

1. Oxygen is absorbed in the alveoli (a passive process; dead people can do this)

2. CO2 is exchanged in the opposite direction, but NOT as readily, largely because it's nice and soluble in blood and likes to stay there unless we maintain a steep A-a gradient

3. Since we're sucking more gas out of the alveoli than we're putting back, a negative pressure develops there

4. Negative pressure sucks gas out of the pharynx, where we've been storing lots of pure oxygen

5. This gradient continues to flow until so much CO2 builds up that we no longer have a negative pressure (plus, um, it's bad for you).

 

[Carlos Danger]

Filling the pharynx with passively-insufflated oxygen is a safety net. You shouldn't be relying on it, and you should be doing your best not to need it. But it takes little time and has negligible harms, and may help "cover your mistakes" when you're not perfect, which is exactly the sort of thing that's helpful for building a layered approach -- you want stuff you don't have to think about behind the stuff you're actively working on.

I completely agree. Placing an NC before you intubate will almost certainly not hurt, and it just may help in some cases. If I were a medical director it would be in my agencies' protocols.

However, I'm sure you would concede that there are times that it just won't help much or at all. Nothing is perfect, right? All I'm saying is that those times are likely to be the times that you need it most.

 

[Brandon O]

However, I'm sure you would concede that there are times that it just won't help much or at all. Nothing is perfect, right? All I'm saying is that those times are likely to be the times that you need it most.

Certainly possible. I would like to see more data on this in sicker folks, but of course, it's hard to do those studies. It'd probably have to be something like an outcome analysis of a big cohort where you randomized half the folks to get the cannula and see whose sats dropped the most, who did better, etc.