Table 2.

Respiratory variables at different study times

	Pre-PP		PP		Post-PP		ANOVA
	n		n		n		p
PEEPt, cmH2O All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	201 142 59 75 81	14 ± 3 14 ± 3 14 ± 3 14 ± 3 15 ± 3	201 142 59 75 81	14 ± 3 14 ± 3 14 ± 3 14 ± 3 15 ± 3	137 99 38 49 52	14 ± 3 14 ± 3 14 ± 3 14 ± 3 15 ± 3	0.652 0.288 0.444 0.889 0.643
Pplat, cmH2O All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	201 142 59 75 81	29 ± 4 29 ± 4 29 ± 4 29 ± 4 28 ± 3	201 142 59 75 81	28 ± 4 28 ± 4 28 ± 4$ 28 ± 3 27 ± 4	137 99 38 49 52	29 ± 4 28 ± 3 30 ± 4 29 ± 4 28 ± 3	0.560 0.567 0.003 0.949 0.965
Driving pressure, cmH2O All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	201 142 59 75 81	15 ± 5 15 ± 5 16 ± 6 15 ± 5 14 ± 4	201 142 59 75 81	14 ± 5* 14 ± 5 15 ± 6 15 ± 5 12 ± 4*	137 99 38 49 52	15 ± 6 14 ± 6 16 ± 7 15 ± 5 13 ± 4	0.018 0.129 0.053 0.596 0.008
Crs, mL/cmH2O All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	201 142 59 75 81	30 ± 11 30 ± 10 31 ± 13 30 ± 10 34 ± 11	201 142 59 75 81	33 ± 13*$ 33 ± 12 32 ± 15$ 30 ± 10 38 ± 13*$	137 99 38 49 52	31 ± 9 32 ± 9 29 ± 8 30 ± 8 33 ± 9	0.001 0.569 0.021 0.927 0.002
PaO2/FiO2, mmHg All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	201 142 59 75 81	109 ± 31 106 ± 31 115 ± 30 115 ± 33 107 ± 29	201 142 59 75 81	163 ± 65*$ 185 ± 61*$ 110 ± 32 161 ± 61*$ 168 ± 72*$	137 99 38 51 51	135 ± 54¤ 143 ± 53¤ 113 ± 51 129 ± 49 139 ± 62¤	< 0.001 < 0.001 0.486 < 0.001 < 0.001
AOP, cmH2O All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	156 106 50 75 81	0 (0–6) 1 (0–6) 0 (0–6) 0 (0–6) 1 (0–6)	158 113 45 59 69	2 (0–6) 2 (0–5) 2 (0–5) 2 (0–5) 2 (0–7)	107 78 29 40 45	3 (0–6) 3 (0–6) 4 (2–6) 3 (0–6) 3 (0–6)	0.375 0.799 0.232 0.406 0.803
R/I All O2-responders O2-nonresponders Lower-recruiters Higher-recruiters	156 106 50 75 81	0.53 (0.31–0.81) 0.53 (0.29–0.76) 0.53 (0.40–0.85) 0.30 (0.00–0.43) 0.76 (0.61–1.16)	158 113 45 59 69	0.51 (0.30–0.76) 0.48 (0.30–0.70) 0.61 (0.36–0.83) 0.45 (0.27–0.71)* 0.57 (0.40–0.86)*	107 78 29 40 45	0.54 (0.27–0.85) 0.54 (0.27–0.88) 0.53 (0.26–0.79) 0.45 (0.04–0.88)¤ 0.62 (0.46–0.84)	0.344 0.241 0.247 0.006 0.019

ANOVA analysis of variance; AOP airway opening pressure; Crs respiratory system compliance; FiO₂ inspired fraction in oxygen; PEEPt total positive end-expiratory pressure; PaO₂ arterial partial pressure in oxygen; PP prone position; Pplat plateau pressure; R/I recruitment-to-inflation ratio

“Pre-PP”: ≤1 h before the PP; “PP”: at the end of the PP session; “Post-PP”: 6 to 8 h after returning to the supine position

* p < 0.05 pre-PP vs. PP, ^$p < 0.05 PP vs. Post-PP, ^¤p < 0.05 pre-PP vs. post-PP