Naked Science Forum
Life Sciences => Physiology & Medicine => COVID-19 => Topic started by: chris on 07/04/2020 09:37:13
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Intensive care units handling covid19 patients are nursing and ventilating the patients prone. What is the physiological and/or anatomical rationale for this manoeuvre?
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I'm sure your friendly local anesthetist will tell you, when she has time!
My guess is some or all of: straighter bronchus (once the intubation is complete) less problem with nasal or postnasal drip, less drag on the face, better seal, less aerosol from cough reflex.
If you find out, please do tell!
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I'm very grateful to my friend and colleague Dr Ari Ercole, from Cambridge University / Addenbrooke's Hospital, who provided this extremely clear explanation:
As far as proning is concerned this has gone back years with nobody finding a survival benefit (although it improves oxygenation) until the attached study1 which changed things suggesting it was a good idea if you do it early in ARDS and combine it with modern ventilation strategies which try to protect the lungs from mechanical trauma.
The way it works is through improving V/Q [Ventilation / perfusion] mismatch. Under normal circumstances, gravity means that the lowest (or back if you’re lying down) bits of the lungs tend to get a little more blood flow because the blood pressure decreases with height above the heart. At the same time, the low bits tend to be mechanically collapsed (think holding a damp sponge by a corner- the top is stretched and the bottom squashed). This means we tend to see collapse, pulmonary oedema and consolidation mostly on the lower (/back) bits of the lung. So we have an unfortunate situation where the blood is preferentially going to bits of lung that aren’t aerated very well (although hypoxic vasoconstriction may partially offset this).
Proning reverses that and sends blood to the aerated bits / re-expands collapsed lung. Unfortunately it’s not easy- very hard and dangerous to flip someone critically ill on a ventilator over (risk of accidentally pulling out the endotracheal tube, lines etc). Also there’s a risk of pressure sores and the facial oedema you see is marked. So we usually prone for 16 hours out of 24 or so. A lot of hospitals are putting together ‘proning teams’ because it needs a lot of skilled manpower.
1. Prone Positioning in Severe Acute Respiratory Distress Syndrome, Claude Guérin et al., NEJM 368 p.2159
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Now that is well observed and very clever!