Table 4.

Mixed effect cox regression analysis on 28 day mortality.

Univariate mixed effect cox regression	Hazard ratio (95% CI)	P value
LTVV	0.67 (0.51 to 0.88)	0.005
Age, years	1.07 (1.05 to 1.08)	<0.001
Male gender	1.30 (0.97 to 1.75)	0.078
Arterial pH	0.00 (0.00 to 0.00)	<0.001
Heart rate, bpm	1.02 (1.01 to 1.02)	<0.001
Acute kidney injury	2.72 (2.11 to 3.52)	<0.001
Respiratory compliance, mL/cm H2O	0.99 (0.98 to 1.01)	0.387
Use of prone positioning	1.14 (0.88 to 1.46)	0.317
Moderate vs Mild ARDSa	1.39 (0.98 to 1.97)	0.063
Severe vs Mild ARDSa	2.24 (1.44 to 3.49)	<0.001
Thrombotic events	1.26 (0.97 to 1.63)	0.083
Multivariate mixed effect cox regression	Hazard ratio (95% CI)	P value
LTVV	0.68 (0.49 to 0.95)	0.025
Age, years	1.06 (1.04 to 1.07)	<0.001
Male gender	1.13 (0.81 to 1.59)	0.471
Arterial pH	0.01 (0.00 to 0.06)	<0.001
Heart rate, bpm	1.01 (1.00 to 1.02)	0.007
Acute kidney injury	2.00 (1.47 to 2.73)	<0.001
Respiratory compliance, mL/cm H2O	1.00 (0.99 to 1.01)	0.821
Use of prone positioning	0.82 (0.60 to 1.13)	0.221
Moderate vs Mild ARDSa	1.30 (0.88 to 1.91)	0.191
Severe vs Mild ARDSa	1.72 (1.01 to 2.92)	0.047
Thrombotic events	1.05 (0.78 to 1.41)	0.746

All models were mixed-effect models with centres as frailty and considering a binomial distribution. Continuous variables were centered. The hazard ratios show the increase in one SD of the variable.

Abbreviations, LTVV: Low tidal volume ventilation;

^aBerlin definition: Mild ARDS P/F ratio > 200 mmHg, Moderate ARDS: 101 < P/F ratio < 200 mmHg, Severe ARDS: P/F ratio < 100 mmHg.