Physiologic effects of prone positioning on gas exchange and ventilation-perfusion matching in awake patients with AHRF

Abstract Background Prone positioning (PP) improves oxygenation in awake patients with acute hypoxemic respiratory failure (AHRF). However, the underlying mechanisms remain unclear in patients with diverse lung morphology. We aimed to determine the short-term effects of awake prone positioning (APP) in AHRF patients with focal and non-focal lung morphology. Methods This is a prospective physiological study. Twenty-four non-intubated patients with PaO2/FiO2 ≤ 300 mm Hg were included. Gas exchange, ventilation and perfusion distribution, and hemodynamics variables were recorded in the supine position (SP1), 2 h after PP, and 1 h after re-supine (SP2). Lung morphology was classified as focal and non-focal patterns using computed tomography. Results Twelve of the included patients were classified to the focal group and 12 to the non-focal group. PaO2/FiO2 improved after PP in all patients (161 137, 227 mmHg vs. 236 202, 275 mmHg, p p p p < 0.001), whereas no difference was found in the non-focal group after PP. Conclusions APP improves V/Q matching by decreasing dead space in patients with focal lung morphology, and by decreasing shunt in patients with non-focal lung morphology. Trial registration: The study is registered in ClinicalTrials.gov (NCT04754113).