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 lung areas alternatively recruited or collapsed with PP sessions can be monitored by electrical impedance tomography (EIT),5 and this monitoring of regional ventilation can be a predictive parameter of improved oxygenation during PP.6 The variation of regional ventilation in the dorsal dependent lung with PP followed by SP has been previously demonstrated with EIT but not continuously between the first and the last PP sessions (PPfirst and PPlast) of subjects with ARDS.6,7 The aim of this study was to see with EIT if there is a stabilization of the dependent dorsal lung aeration day after day in SP after PP between PPfirst and PPlast sessions. This study was approved by the Ethical Committee CER-BDX-2023-01. Inclusion criteria were subjects with ARDS, intubated, sedated, and ventilated in volume controlled ventilation with … Correspondence: Hadrien Rozé MD PhD, Réanimation Polyvalente, Centre Hospitalier Côte Basque, F64100, Bayonne, France. E-mail: hadrien.roze{at}chu-bordeaux.fr