Awake prone positioning improves ventilation distribution in patients with acute respiratory failure: a prospective physiological study

Background: Since the beginning of the coronavirus disease 2019 (COVID-19) pandemic, prone positioning has been widely applied for non-intubated, spontaneously breathing patients. Many clinical studies have shown that awake prone positioning (APP) can reduce the intubation rate and help improving the prognosis of patients with acute hypoxemic respiratory failure (ARF), but its physiological mechanism is still unknown. In our study, we aimed to evaluate the effect of APP on lung ventilation in patients with moderate to severe ARF, trying to reveal the effects on ventilation distribution and oxygenation in non-intubated patients. Measurements: The study included patients with ARF (PaO 2 /FiO 2 < 200mmHg or SpO 2 /FiO 2 < 235) treated with high-flow nasal oxygen (HFNC). EIT measurements were performed in the supine position (T0), 0.5 h after the start of APP (T1) and at 0.5 h returning to supine position after the APP (T2). Results: : Based on EIT measurements, it was observed that the distribution of ventilation was more uniform after prone positioning, and prone positioning significantly improved the ventilation of dorsal regions. Ventilation redistributed from the ventral to dorsal area (48.77% vs 54.79% vs 50.34%, P=0.030), global inhomogeneity (GI) index decreased significantly after the end of prone positioning therapy (48.17% vs 42.60% vs 28.21%, P=0.049), regional ventilation delay (RVD) changes are not obvious (5.24% vs 4.47% vs 4.35%, P=0.794). Conclusions: Awake prone positioning can improve ventilation distribution and homogeneity of lung ventilation assessed by electrical impedance tomography in non-intubated patients with acute respiratory failure.