How does prone positioning affect oxygenation in severe ARDS?

• A. Improves oxygenation by redistributing lung perfusion and recruiting dorsal lung segments
• B. Worsens oxygenation
• C. Has no effect on oxygenation
• D. Only beneficial in mild ARDS

Answer: (A)

Prone positioning improves oxygenation in severe ARDS by enhancing ventilation-perfusion matching through dorsal recruitment and more favorable chest wall mechanics. When a patient is turned prone, the posterior (dorsal) lung, which tends to be collapsed and edematous in ARDS when supine, becomes nondependent and can expand more fully. The heart and mediastinal structures shift away from compressing the posterior lung, reducing regional atelectasis. Perfusion tends to remain relatively consistent, so better aeration of the dorsal regions means blood is flowing through more ventilated units, lowering shunt and raising arterial oxygen levels. This effect is especially pronounced in severe ARDS, where dorsal collapse is most extensive, and it is not limited to mild disease. While responses can vary, prone positioning generally improves oxygenation rather than worsening it, and its benefits are rooted in more uniform lung inflation and improved V/Q matching.