Comparison 1. Dose of opioid‐based cardiac anaesthesia.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Mortality	8		Peto Odds Ratio (Peto, Fixed, 95% CI)	Subtotals only
1.1 Death in hospital after surgery	7	1896	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.58 [0.24, 1.39]
1.2 Death at 1 year after surgery	2	446	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.55 [0.17, 1.82]
1.3 Death at any time after surgery	8	1994	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.53 [0.25, 1.12]
2 Postoperative complications	10		Risk Ratio (IV, Random, 95% CI)	Subtotals only
2.1 Postoperative myocardial infarction	8	1683	Risk Ratio (IV, Random, 95% CI)	0.98 [0.48, 1.99]
2.2 Stroke	5	562	Risk Ratio (IV, Random, 95% CI)	1.17 [0.36, 3.78]
2.3 Acute renal failure	4	492	Risk Ratio (IV, Random, 95% CI)	1.19 [0.33, 4.33]
2.4 Major bleeding	4	469	Risk Ratio (IV, Random, 95% CI)	0.48 [0.16, 1.44]
2.5 Reintubation	5	594	Risk Ratio (IV, Random, 95% CI)	1.77 [0.38, 8.27]
3 Service outcomes	14		Mean Difference (IV, Random, 95% CI)	Subtotals only
3.1 Time to extubation (hours)	14	2486	Mean Difference (IV, Random, 95% CI)	‐7.40 [‐10.51, ‐4.29]
3.2 Length of intensive care unit stay (hours)	12	1394	Mean Difference (IV, Random, 95% CI)	‐3.70 [‐6.98, ‐0.41]
3.3 Length of hospital stay (days)	8	913	Mean Difference (IV, Random, 95% CI)	‐0.30 [‐1.04, 0.43]