Daily Evolution of Lung Dependent–Area Collapse Between Prone Position Sessions in ARDS Evaluated by Electrical Impedance Tomography
In ARDS, several prolonged sessions of prone position (PP) can improve survival.1 The major reason for proning patients is hypoxemia.2,3 Pulmonary edema increases the lung weight, and the consequence is a progressive increase in pressure along the vertical axis that squeezes gas from the most dependent dorsal lung units (de-recruitment). These units become gasless in supine position (SP), and this process is reversed by PP (recruitment). Indeed, with computed tomography scan, shifting from supine to PP led immediately to the inversion of the inflation gradient and to a redistribution of densities from dorsal to ventral lung regions.4 With PP, the dorsal pulmonary units tend to open while the ventral units, previously open, tend to collapse. When back in SP, the dorsal pulmonary units tend to reopen while the ventral units, previously open, tend to recollapse but not in a 1:1 ratio. Indeed, we expect a stabilization of dorsal lung aeration in patients recovering from ARDS. The dependent