Why do some critically ill patients, when they are laid flat for intubation, either get worse or sometimes even go into cardiac arrest?
Patients with CHF, COPD, and morbid obesity are considered susceptible. I am not sure what I have read in the literature is correct in explaining it. I suspect that anyone who lays flat has more air trapping. This can crowd out venous return. In a patient on the brink of dying, impairing venous return might put them over that brink.
An interesting corollary of this idea is that patients with high autoPEEP on a ventilator can be placed in the upright position and this significantly reduces their autoPEEP.
So in summary, supine positioning appears to exacerbate auto-PEEP, and in the peri-arrest state can precipitate cardiac arrest apparently through crowding out venous return
Take Home Points
-Supine positioning causes autoPEEP
-In the patient with a respiratory life threat, keep the patient upright as long as possible.
-Consider 30 degrees elevation (reverse Trendelenburg) for intubating patients thought to have potential for arrest during intubation
-In the ventilated patient who develops auto-PEEP, use reverse Trendelenburg or upright posture as a treatment
Khandelwal N, Khorsand S, Mitchell SH, Joffe AM.
Anesth Analg. 2016 Apr;122(4):1101-7