Fig. 1

Individual Partial Pressure of Arterial Oxygen (PaO₂) Variation in Supine responders (left) and Supine non-responders (right). In both groups solid lines represent prone responders, dashed lines prone non-responders (see Text for definitions). Red bars represent median PaO₂ values in each decubitus, and P values (* when significant) refer to their comparisons. As shown, 14 patients (50%) were supine responders (median PaO₂ increase from seated to supine: 31 [26–44] mmHg). Among these, one did not tolerate proning, six were prone responders (median PaO₂ increase from supine to prone: 67 [60–92] mmHg) and seven were prone non-responders (one worsened oxygenation during proning, while the 6 patients highlighted by green dots benefit from recumbency irrespective of supine or prone position specifically). The remaining 14 patients (50%) were supine non-responders. Among these, 5 were prone responders (median PaO₂ increase from supine to prone: 31 [30–68] mmHg), while in the 9 remaining subjects, PaO₂ did not significantly change between supination and proning