Effect of prone positioning on gas exchange according to lung morphology in patients with acute respiratory distress syndrome

Background: There are limited data on the clinical effects of prone positioning according to lung morphology. We aimed to determine whether the gas exchange response to prone positioning dif-fers according to lung morphology. Methods: This retrospective study included adult patients with moderate-to-severe acute respira-tory distress syndrome (ARDS). The lung morphology of ARDS was assessed by chest computed to-mography scan and classified as & ldquo;diffuse & rdquo; or & ldquo;focal.& rdquo; The primary outcome was change in partial pressure of arterial oxygen to fraction of inspired oxygen (PaO2/FiO2) ratio after the first prone po-sitioning session: first, using the entire cohort, and second, using subgroups of patients with dif-fuse ARDS matched 2 to 1 with patients with focal ARDS at baseline. Results: Ninety-five patients were included (focal ARDS group, 23; diffuse ARDS group, 72). Before prone positioning, the focal ARDS group showed worse oxygenation than the diffuse ARDS group (median PaO2/FiO2 ratio, 79.9 mm Hg [interquartile range (IQR)], 67.7 & ndash;112.6 vs. 104.0 mm Hg [IQR, 77.6 & ndash;135.7]; P=0.042). During prone positioning, the focal ARDS group showed a greater improve-ment in the PaO2/FiO2 ratio than the diffuse ARDS group (median, 55.8 mm Hg [IQR, 11.1 & ndash;109.2] vs. 42.8 mm Hg [IQR, 11.6 & ndash;83.2]); however, the difference was not significant (P=0.705). Among the PaO2/FiO2-matched cohort, there was no significant difference in change in PaO2/FiO2 ratio af-ter prone positioning between the groups (P=0.904). Conclusions: In patients with moderate-to-severe ARDS, changes in PaO2/FiO2 ratio after prone positioning did not differ according to lung morphology. Therefore, prone positioning can be con-sidered as soon as indicated, regardless of ARDS lung morphology. <comment>Superscript/Subscript Available</commentN