Comparison 1. Cell salvage ‐ blood transfused (all studies).

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 No. exposed to allogeneic blood (All Studies)	67	6025	Risk Ratio (M‐H, Random, 95% CI)	0.62 [0.55, 0.70]
2 No. exposed to allogeneic blood (Transfusion Protocol)	67		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
2.1 Transfusion Protocol	52	4755	Risk Ratio (M‐H, Random, 95% CI)	0.62 [0.54, 0.71]
2.2 No Transfusion Protocol	15	1270	Risk Ratio (M‐H, Random, 95% CI)	0.58 [0.41, 0.82]
3 No. exposed to allogeneic blood (Type of Surgery)	67		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
3.1 Cardiac	31	2518	Risk Ratio (M‐H, Random, 95% CI)	0.77 [0.69, 0.86]
3.2 Orthopaedic	32	3240	Risk Ratio (M‐H, Random, 95% CI)	0.46 [0.37, 0.57]
3.3 Vascular	4	267	Risk Ratio (M‐H, Random, 95% CI)	0.63 [0.34, 1.15]
4 No. exposed to allogeneic blood ‐ (Washed vs Unwashed)	67		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
4.1 Washed	27	2225	Risk Ratio (M‐H, Random, 95% CI)	0.60 [0.51, 0.70]
4.2 Unwashed	40	3717	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.57, 0.77]
5 No. exposed to allogeneic blood (Timing)	66		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
5.1 Intra‐operative cell salvage	11	805	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.46, 0.76]
5.2 Post‐operative cell salvage	46	4361	Risk Ratio (M‐H, Random, 95% CI)	0.63 [0.54, 0.74]
5.3 Intra & post‐operative cell salvage	9	737	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.54, 0.92]
6 Units of allogeneic blood transfused (All Studies)	32	2321	Mean Difference (IV, Random, 95% CI)	‐0.68 [‐0.88, ‐0.49]
7 Units of allogeneic blood transfused (Transfusion Protocol)	32		Mean Difference (IV, Random, 95% CI)	Subtotals only
7.1 Transfusion Protocol	27	1950	Mean Difference (IV, Random, 95% CI)	‐0.69 [‐0.90, ‐0.49]
7.2 No Transfusion Protocol	5	371	Mean Difference (IV, Random, 95% CI)	‐0.64 [‐1.30, 0.01]
8 Units of allogeneic blood transfused (Type of Surgery)	32		Mean Difference (IV, Random, 95% CI)	Subtotals only
8.1 Cardiac	19	1497	Mean Difference (IV, Random, 95% CI)	‐0.67 [‐0.89, ‐0.44]
8.2 Orthopaedic	10	638	Mean Difference (IV, Random, 95% CI)	‐0.81 [‐1.22, ‐0.39]
8.3 Vascular	3	186	Mean Difference (IV, Random, 95% CI)	0.02 [‐0.34, 0.38]