Outcome	No of trials	No of participants	Treatment Effect			Heterogeneity
			Ratio of means*	(95% CI)	P value	I² (%)
Day one (24 hours)
PaO₂/FiO₂†	8	1156	1.26	(1.15 to 1.38)	< 0.00001	47
Mean airway pressure	9	985	1.30	(1.26 to 1.35)	< 0.00001	23
Oxygenation index	7	423	1.10	(0.97 to 1.25)	0.14	43
PaCO₂	10	1767	0.95	(0.87 to 1.05)	0.32	90
Day two (48 hours)
PaO₂/FiO₂†	6	1031	1.18	(1.04 to 1.35)	0.01	66
Mean airway pressure	7	888	1.25	(1.19 to 1.31)	< 0.00001	38
Oxygenation index	6	375	1.06	(0.89 to 1.26)	0.54	58
PaCO₂	8	1587	0.93	(0.81 to 1.06)	0.25	96
Day three (72 hours)
PaO₂/FiO₂†	6	881	1.21	(1.09 to 1.35)	0.0005	55
Mean airway pressure	7	338	1.16	(1.06 to 1.27)	0.001	58
Oxygenation index	6	330	1.05	(0.85 to 1.29)	0.66	68
PaCO₂	7	920	1.00	(0.88 to 1.14)	0.99	93
Footnotes PaO₂/FiO₂ = ratio of arterial partial pressure of oxygen to fraction of inspired oxygen; PaCO₂ = arterial partial pressure of carbon dioxide. †In one trial (Mentzelopoulos 2012) in which high‐frequency oscillation was used for variable duration according to a prespecified protocol, the mean (and standard error) of the average daily measurements for each participant were used in lieu of the mean of a single value for each participant measured at a similar time point. *Mean value in high‐frequency oscillation group divided by mean value in conventional ventilation group. Random‐effects models used for all meta‐analyses.