Impact of Visceral Fat on Oxygenation Response to Prone Positioning in Mechanically Ventilated Patients With Severe COVID-19.

Background Prone positioning therapy is internationally recommended as a cost-effective method to improve oxygenation and reduce mortality in patients with severe acute respiratory distress syndrome. This study investigated whether visceral fat (VF) area is associated with changes in oxygenation during prone positioning in mechanically ventilated patients with severe COVID-19 pneumonia. We further assessed whether VF modifies the magnitude of the oxygenation response to prone positioning. Methods We conducted a retrospective observational study of 89 critically ill COVID-19 patients who received mechanical ventilation and prone positioning therapy at a university hospital from April 2020 to November 2021. VF area was automatically quantified from admission chest CT, and patients were classified into high and low VF groups using a 100 cm² cutoff. The primary outcome was the ratio of the partial pressure of oxygen in arterial blood (PaO2) and fraction of inspiratory oxygen (FiO2) (P/F ratio) at four time points. Secondary outcomes included extracorporeal membrane oxygenation (ECMO) use. A multilevel analysis was performed to determine if VF area modified the therapy's effectiveness, adjusting for covariates. An interaction term was included to assess whether the effect of prone positioning on oxygenation differed by VF level. Results Among 89 patients, baseline P/F ratios were similar between the low and high VF groups (147 vs 138). During prone positioning, oxygenation improved in both groups, and the low VF group showed a significantly higher P/F ratio than the high VF group (279 vs 228; p = 0.016). Interaction analysis showed that the difference in P/F ratios between groups was significantly greater during the prone positioning phase, suggesting that prone positioning amplified the effect of VF on oxygenation. This difference was no longer observed after returning to the supine position (181 vs 195). No significant differences were observed in ECMO use between the groups. Conclusion In severe COVID-19 pneumonia, the low VF group experienced significantly better oxygenation during prone positioning than the high VF group, with the difference being more pronounced during the prone phase. This difference was not observed after returning to the supine position. Prone positioning did not reduce the probability of ECMO initiation. Future studies should evaluate whether VF assessment can guide individualized prone positioning strategies and improve outcome-oriented patient selection.