Early physiologic changes after awake prone positioning predict clinical outcomes in patients with acute hypoxemic respiratory failure

Purpose: The optimal physiologic parameters to monitor after a session of awake prone positioning in patients with acute respiratory failure are not well understood. This study aimed to identify which early physiologic changes after the first session of awake prone positioning are linked to the need for invasive mechanical ventilation or death in patients with acute respiratory failure. Methods: We performed a secondary analysis of a prospective cohort study of adult patients with acute respiratory failure related to coronavirus disease 2019 (COVID-19) treated with awake prone positioning. We assessed the association between relative changes in physiological variables (oxygenation, respiratory rate, pCO2 and respiratory rate-oxygenation [ROX] index) within the first 6 h of the first awake prone positioning session with treatment failure, defined as endotracheal intubation and/or death within 7 days. Results: 244 patients [70 female (29%), mean age 60 (standard deviation [SD] 13) years] were included. Seventy-one (29%) patients experienced awake prone positioning failure. ROX index was the main physiologic predictor. Patients with treatment failure had lower mean [SD] ROX index at baseline [5 (1.4) versus 6.6 (2.2), p < 0.0001] and within 6 h of prone positioning [5.6 (1.7) versus 8.7 (2.8), p < 0.0001]. After adjusting for baseline characteristics and severity, a relative increase of the ROX index compared to baseline was associated with lower odds of failure [odds ratio (OR) 0.37; 95% confidence interval (CI) 0.25–0.54 every 25% increase]. Conclusion: Relative changes in the ROX index within 6 h of the first awake prone positioning session along with other known predictive factors are associated with intubation and mortality at day 7.