Figure 1

Time course of changes in the PaO ₂ /FiO ₂ ratio (PFR) during the first 40 h of prone positioning (PP). Analysis of variance (ANOVA) was used to compare values among the various time points. Multiple comparisons were performed using Dunnett’s tests with baseline values (before PP; supine position) as reference values. The paired t-test was also used to compare the values at 8 h with those at 16 h. Supine represents immediately before starting prone positioning (*p < 0.05 vs. reference). SD standard deviation.