Sunday, April 12, 2020

Are the "Vent Protocols" causing harm in COVID?

Here is a response to Deborah Mayo's excellent blog post posing this question.  I encourage you to first read her post.  Here, I explicate my view of the problems that are raised in that post.  I don't have time for a lot of hot links and stuff, so post your specific comments below.

There is a lot correct here, and @learnfromerror has done a far better job of summarizing it than I could ever explain a normal distribution. But there is a lot missing, because the commentators have not gotten to the crux, and have made slogans for their points that are distracting and misguided if not totallly incorrect.

First, and this is very very important, is that *there are NO protocols for intubation* as the NYC ER doctor suggests. I talk about that on my other blog a lot. ARDS trials enroll patients who are *already intubated* and the criteria for that intubation are absent from the study protocols. It is assumed in an ARDS study that if you are intubated, you were appropriately intubated. Therefore, there is no “problem with the protocols” for ventilators, there is a glaring and longstanding problem with the criteria (or the absence of criteria) for intubating patients. Is it blood gas values, or vital signs, or physical examination signs, or subjective distress or some combination? There is ZERO standardization in this area. COVID has brought this underappreciated problem to the fore.

Why is this just coming out now? Ah, that’s another crux of the problem and a reason that COVID has become a perfect storm for ventilator management. Usually, if you intubate a little old lady with influenza, even if you do it for shaky reasons, she can be extubated (tube removed) in a couple of days or a week with little harm done (or with a level of harm that we take for granted, probably mistakenly). Not so with COVID. The natural history of the disease has 2 important features that make the decision to intubate likely to culminate in a massive therapeutic misadventure: 1.) the duration of the illness is protracted, two to perhaps as long as four weeks; and 2.) the level of sedation needed to counteract the massive air hunger these patients have, for the duration they need it, is through the roof.  This problem is compounded by the mandate to use small tidal volumes which are poorly tolerated in the face of massive air hunger. So, 2 weeks after intubation, they are veritable zombies, cannot be weaned from sedatives (a prerequisite from being weaned from the ventilator), and are stuck on the vent, assuming that before this stage other complications have not set in and/or death ensued.

Another facet of the perfect storm, which I think is also the Rosetta Stone, and a key to untangling this giant mess we find ourselves in, is that this normal lung compliance that people are talking about is *the reason why* there is this so-called “silent hypoxemia” of the type mentioned by the ER doc in Mayo’s post. Failure to recognize this connection betrays a common misunderstanding of respiratory physiology (my attempt to disabuse people of these errors can be found here: Dyspnea is not driven by hypoxemia as much as it is by hypercarbia, which can be compensated for by hyperventilation which these patients are doing! To a person who has a firm grasp on applied respiratory physiology, this is no surprise – the patients have compliant lungs, so they don’t have workload imbalance and can sustain ventilation in the face of significant hypoxemia (which is a MINOR driver of dyspnea) very well. In sum, I am not surprised by these clinical presentations, nor am I surprised that this quagmire has allowed problems with the understanding of applied respiratory physiology to surface.

This disease is very difficult for these and many other reasons. When the choice is let a hypoxemic person who is defending her CO2 - like the little old lady the ER doc talks about - ride it out (which she can probably do for a very long time, see my tweets about sustaining very high Ve indefinitely [50% of the 15-second MVV]), versus intubating her for a marginal gain in gas exchange accompanied by a massive cost in sedation and paralysis, the choice is clear, let them ride it out, don't incur that cost.

The problem is not with the “vent protocols” the problem lies in a widespread lack of understanding of applied respiratory physiology which leads to questionable calls regarding intubation which are usually, in non-pandemic times, lost in the signal and noise of the fray. Not so with COVID – premature or unnecessary intubations precipitate a cascade of status iatrogenicus.

1 comment:

  1. Here is Gattinoni's letter:

    I agree completely with his assessment of the physiology (compliance, shunt, vascular perfusion changes), however I disagree with his suggestion that we should intubate the patients to usurp control and replace negative pressure ventilation with positive pressure ventilation, something that seems absurd and which no study to my knowledge has ever addressed.

    Finally, I think he misses completely my analysis presented above about these decisions reflecting trade-offs.

    I agree that prone positioning and high PEEP are likely to be harmful on balance.


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