Table 2.

Summary of the subgroup analyses in observational studies

Subgroups	Number of studies	Sample size	OR	95% CI	P	I2
Definition of antiplatelet therapy
Aspirin only	3	5379	0.67	(0.52–0.86)	0.829	0.0%
Aspirin in combination	4	1848	0.67	(0.44–1.02)	0.003	78.8%
Time of antiplatelet therapy
Before hospitalization	3	5379	0.67	(0.52–0.86)	0.829	0.0%
Before and/or after hospitalization	4	1848	0.67	(0.44–1.02)	0.003	78.8%
Risk factors for ARDS
Sepsis
Yes	5	5703	0.69	(0.50–0.95)	0.004	74.3%
No	2	1524	0.64	(0.46–0.90)	0.603	0.0%
Shock
Yes	3	4834	0.74	(0.52–0.88)	0.062	63.9%
No	4	2393	0.61	(0.48–0.77)	0.364	5.8%
Pneumonia
Yes	3	4834	0.74	(0.52–0.88)	0.062	63.9%
No	4	2393	0.61	(0.48–0.77)	0.364	5.8%
Aspiration
Yes	3	4834	0.74	(0.52–0.88)	0.062	63.9%
No	4	2393	0.61	(0.48–0.77)	0.364	5.8%
Trauma
Yes	3	4834	0.74	(0.52–0.88)	0.062	63.9%
No	4	2393	0.61	(0.48–0.77)	0.364	5.8%
High-risk surgery
Yes	3	1411	0.90	(0.85–0.95)	0.609	0.0%
No	4	5816	0.59	(0.48–0.73)	0.352	8.2%
Pancreatitis
Yes	3	4834	0.74	(0.52–0.88)	0.062	63.9%
No	4	2393	0.61	(0.48–0.77)	0.364	5.8%
Massive transfusion
Yes	1	218	0.91	(0.49–1.69)	–	–
No	5	7009	0.65	(0.48–0.87)	0.002	73.6%
Definition of ARDS
Berlin definition	1	375	0.46	(0.12–1.74)	–	–
AECC definition	5	6634	0.66	(0.48–0.89)	0.001	77.9%
The 2004 consensus definition of TRALI	1	218	0.91	(0.49–1.69)	–	–
Size of the population
Small	5	2223	0.65	(0.44–0.98)	0.004	73.5%
Large	2	5004	0.68	(0.52–0.88)	0.819	0.0%
Study design
Prospective cohort	2	2502	0.68	(0.52–0.88)	0.819	0.0%
Retrospective cohort	3	1187	0.48	(0.35–0.66)	0.758	0.0%
Case–control study	2	1036	0.90	(0.85–0.95)	0.972	0.0%

ARDS acute respiratory distress syndrome, AECC American-European Consensus Conference, TRALI transfusion-related acute lung injury