Comparison 6. Active vs no active (subgroup analysis by timing of intervention).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Infection and complications of the surgical wound	2	479	Risk Ratio (M‐H, Random, 95% CI)	0.36 [0.20, 0.66]
1.1 Intraoperative	1	200	Risk Ratio (M‐H, Random, 95% CI)	0.31 [0.13, 0.74]
1.2 Preoperative	1	279	Risk Ratio (M‐H, Random, 95% CI)	0.42 [0.19, 0.92]
2 Major cardiovascular complications (cardiovascular death, non‐fatal myocardial infarction, non‐fatal stroke, and non‐fatal cardiac arrest)	1	300	Risk Ratio (M‐H, Random, 95% CI)	0.22 [0.05, 1.00]
3 Non‐fatal myocardial infarction	1	300	Risk Ratio (M‐H, Random, 95% CI)	0.37 [0.02, 9.03]
4 Non‐fatal cardiac arrest	1	300	Risk Ratio (M‐H, Random, 95% CI)	0.22 [0.05, 1.00]
5 Blood transfusions during surgery and up to 48 hours post‐surgery (mL)	5	404	Mean Difference (IV, Random, 95% CI)	‐35.82 [‐82.87, 11.23]
6 Participants transfused	6	465	Risk Ratio (M‐H, Random, 95% CI)	0.89 [0.56, 1.42]
7 Blood loss during surgery ‐ mL	16	963	Mean Difference (IV, Random, 95% CI)	‐57.02 [‐97.69, ‐16.35]
7.1 Intraoperative	14	893	Mean Difference (IV, Random, 95% CI)	‐66.70 [‐106.62, ‐26.79]
7.2 Pre + Intraoperative	2	70	Mean Difference (IV, Random, 95% CI)	‐149.47 [‐613.68, 314.75]
8 Fluids transfused during surgery ‐ mL	17	1079	Mean Difference (IV, Random, 95% CI)	‐178.22 [‐275.00, ‐79.44]
8.1 Intraoperative	12	947	Mean Difference (IV, Random, 95% CI)	‐205.29 [‐287.91, ‐122.67]
8.2 Preoperative	2	32	Mean Difference (IV, Random, 95% CI)	‐243.68 [‐733.52, 246.15]
8.3 Pre + Intraoperative	3	100	Mean Difference (IV, Random, 95% CI)	‐68.07 [‐323.57, 187.43]
9 Participant's anxiety and state	1	130	Mean Difference (IV, Random, 95% CI)	0.40 [‐0.57, 1.37]
10 Participant's comfort (thermal) (higher values mean higher comfort)	10	700	Std. Mean Difference (IV, Random, 95% CI)	0.77 [0.19, 1.36]
10.1 Intraoperative	5	410	Std. Mean Difference (IV, Random, 95% CI)	0.73 [‐0.35, 1.82]
10.2 Preoperative	2	205	Std. Mean Difference (IV, Random, 95% CI)	0.53 [0.25, 0.81]
10.3 Pre + Intraoperative	3	85	Std. Mean Difference (IV, Random, 95% CI)	0.99 [‐0.18, 2.17]
11 Pain	5	214	Mean Difference (IV, Random, 95% CI)	0.06 [‐0.71, 0.82]
11.1 Intraoperative	1	29	Mean Difference (IV, Random, 95% CI)	1.0 [‐1.35, 3.35]
11.2 Preoperative	1	100	Mean Difference (IV, Random, 95% CI)	‐0.30 [‐1.02, 0.42]
11.3 Pre + Intraoperative	3	85	Mean Difference (IV, Random, 95% CI)	0.07 [‐1.04, 1.18]
12 Chills/shivering	25	1466	Risk Ratio (M‐H, Random, 95% CI)	0.36 [0.25, 0.53]
12.1 Intraoperative	17	1178	Risk Ratio (M‐H, Random, 95% CI)	0.37 [0.22, 0.63]
12.2 Preoperative	3	132	Risk Ratio (M‐H, Random, 95% CI)	0.34 [0.10, 1.17]
12.3 Pre + Intraoperative	5	156	Risk Ratio (M‐H, Random, 95% CI)	0.30 [0.14, 0.63]
13 All‐cause mortality	2	500	Risk Ratio (M‐H, Random, 95% CI)	1.01 [0.26, 4.00]