Transdiaphragmatic pressures during increasing levels of positive end-expiratory pressure (PEEP; cm H₂O). The data are shown for the entire intervention group (restrictive and liberal group together) at baseline. The results are displayed as estimated marginal means with 95% CI. Bonferroni adjustment was applied to account for multiple testing. In the mixed model, PEEP was applied as a fixed factor. *P = 0.003; P < 0.001; P < 0.001 compared to PEEP 15, PEEP 10, and PEEP 5, respectively. ⁺P = 0.017; P = 0.011 compared to PEEP 10 and PEEP 5, respectively.