EMCrit 277 – COVID Pulmonary Physiology with Martin Tobin

[featimage]

Today on the podcast, I interview Martin Tobin on 3 papers he has recently written on COVID pulmonary physiology.

Martin Tobin

* Praise for Dr. Tobin

* Bio Page

Caution about Early Intubation in COVID-19

p-SILI

From 2 studies, 1 on sheep breathing with a human-equivalent Vt of 502 ml

2nd study was observational with a questionable connection to Vt--it was confounded by a number of other factors

Absence of Obtundation

L vs. H Subtypes

Physio Diversion - Looking for the Patient that needs more Inspiratory Flow

* Tobin Vent Review in NEJM

Basing Respiratory Management of COVID-19 on Physiological Principles

Tachypnea in Isolation is Not an Indication for Intubation

Not indicative of increased WOB

Avoiding Intubation with NIPPV

Correlation of saturation with a host of other evils, but it is possible that the saturation is merely a marker--similar to pH. Vicious cycle of shunt, low SvO2, encephalopathy, decreased resp. drive. COVID has been different, with decreased saturation without the horrible lung injury that normally accompanies it. We are also used to patient discomfort from the disease causing the hypoxemia. Retained good compliance. We have not seen the isolated hypoxemia of COVID in many situations before.

The Baffling Case of Silent Hypoxemia

Happy Hypoxemia vs. Silent Hypoxemia

Dr. Tobin defines silent hypoxemia as PaO2 < 60 mmHg with a PaCO2 >39 mmHg (as a PaCO2 < =39) blunts the dyspneic response to hypoxemia

Why don't they have dyspnea vs. why do they have such severe hypoxemia unaccompanied by the degree of standard badness that normally accompanies it

They do not crump

They don't develop multi-organ

Dyspnea

Purely subjective

Advanced age and diabetes may blunt dypsnea

Increase in 10 of PaCO2 causes extreme air hunger

Increase Ve when PaO2 <60, but severe hypoxemia elicits increase in ventilation only when PaCO2 > 39 mmHg [32539537]

Definition of Hypoxemia

Do we need to factor in FiO2? Dr. Tobin and I say no!

I define by pulse ox or (PaO2), doesn't matter how much O2. e.g. "He is still hypoxemic despite being placed on NRB."

When does Hypoxemia Become Dangerous?

Pulse Ox Inaccuracy

OxyHemoglobin Dissociation Curve Shifts

Fever shifts to the right, Decreased CO2 shifts left

Mechanism of Silent Hypoxemia

ACE2 is expressed in the carotid body and may be partially to blame

COVID breaks our Heuristics

Heuristic representation of how bad their lung disease actually is. Projecting expected course...

COVID first disease that unlinks it

Now on to the Podcast...