Clinical Meaning of Early Oxygenation Improvement in Severe Acute Respiratory Distress Syndrome under Prolonged Prone Positioning

BACKGROUND/AIMS: Ventilating patients with acute respiratory distress syndrome (ARDS) in the prone position has been shown to improve arterial oxygenation, but prolonged prone positioning frequently requires continuous deep sedation, which may be harmful to patients. We evaluated the meaning of early gas exchange in patients with severe ARDS under prolonged (> or = 12 hours) prone positioning. METHODS: We retrospectively studied 96 patients (mean age, 60.1 +/- 15.6 years; 75% men) with severe ARDS (PaO(2)/FiO2 < or = 150 mmHg) admitted to a medical intensive care unit (MICU). The terms "PaO2 response" and "PaCO2 response" represented responses that resulted in increases in the PaO2/FiO2 ratio of > or = 20 mmHg and decreases in PaCO2 of > or = 1 mmHg, respectively, 8 to 12 hours after first placement in the prone position. RESULTS: The mean duration of prone positioning was 78.5 +/- 61.2 hours, and the 28-day mortality rate after MICU admission was 56.3%. No significant difference in clinical characteristics was observed between PaO2 and PaCO2 responders and non-responders. The PaO2 responders after prone positioning showed an improved 28-day outcome, compared with non-responders by Kaplan-Meier survival estimates (p < 0.05 by the log-rank test), but the PaCO12 responders did not. CONCLUSIONS: Our results suggest that the early oxygenation improvement after prone positioning might be associated with an improved 28-day outcome and may be an indicator to maintain prolonged prone positioning in patients with severe ARDS.