Improved Oxygenation After Prone Positioning May Be a Predictor of Survival in Patients With Acute Respiratory Distress Syndrome*

Objectives: Prone position ventilation improves oxygenation and reduces the mortality of patients with severe acute respiratory distress syndrome. However, there is limited evidence about which patients would gain most survival benefit from prone positioning. Herein, we investigated whether the improvement in oxygenation after prone positioning is associated with survival and aimed to identify patients who will gain most survival benefit from prone positioning in patients with acute respiratory distress syndrome. Design: A retrospective cohort study. Setting: Medical ICU at a tertiary academic hospital between 2014 and 2020. Patients: Adult patients receiving prone positioning for moderate-to-severe acute respiratory distress syndrome. Interventions: None. Measurements and Main Results: The main outcomes were ICU and 28-day mortality. A total of 116 patients receiving prone positioning were included, of whom 45 (38.8%) were ICU survivors. Although there was no difference in Pa o 2 :F io 2 ratio before the first prone session between ICU survivors and nonsurvivors, ICU survivors had a higher Pa o 2 :F io 2 ratio after prone positioning than nonsurvivors, with significant between-group difference ( p < 0.001). The area under the receiver operating characteristic curve of the percentage change in the Pa o 2 :F io 2 ratio between the baseline and 8–12 hours after the first prone positioning to predict ICU mortality was 0.87 (95% CI, 0.80–0.94), with an optimal cutoff value of 53.5% (sensitivity, 91.5%; specificity, 73.3%). Prone responders were defined as an increase in Pa o 2 :F io 2 ratio of greater than or equal to 53.5%. In the multivariate Cox regression analysis, prone responders (hazard ratio, 0.11; 95% CI, 0.05–0.25), immunocompromised condition (hazard ratio, 2.15; 95% CI, 1.15–4.03), and Sequential Organ Failure Assessment score (hazard ratio, 1.16; 95% CI, 1.06–1.27) were significantly associated with 28-day mortality. Conclusions: The Pa o 2 :F io 2 ratio after the first prone positioning differed significantly between ICU survivors and nonsurvivors. The improvement in oxygenation after the first prone positioning was a significant predictor of survival in patients with moderate-to-severe acute respiratory distress syndrome.