In this post I will briefly explain and critique their mathematical approach, propose a simpler equation for estimating PEEPi in APRV [based on far fewer physiological assumptions] and finally reaffirm why, in my opinion, driving pressure is a troublesome variable, particularly in APRV. It is entirely possible that a patient with severe ARDS secondary to trauma-induced pancreatitis and a patient with equally severe ARDS from bilateral aspiration pneumonia have the same respiratory mechanics; however, their trans-pulmonary pressures – and therefore stress across the lung – may be markedly different.

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