Comparison 1. Buffered versus non‐buffered.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Mortality (all time frames reported)	3	267	Peto Odds Ratio (Peto, Fixed, 95% CI)	1.85 [0.37, 9.33]
2 Organ system failure ‐ renal insufficiency requiring support	4	267	Odds Ratio (M‐H, Fixed, 95% CI)	0.82 [0.34, 1.98]
3 Urine output (mL)	8		Mean Difference (IV, Random, 95% CI)	Subtotals only
3.1 Intraoperative urine output (mL)	8	459	Mean Difference (IV, Random, 95% CI)	6.10 [‐128.41, 140.61]
3.2 Intraoperative urine output (mL) ‐ sensitivity analysis after exclusion of O'Malley 2005	6	348	Mean Difference (IV, Random, 95% CI)	9.93 [‐147.01, 166.87]
3.3 Renal transplant patients	2	111	Mean Difference (IV, Random, 95% CI)	58.26 [‐446.70, 563.21]
4 Creatinine change (µmol/L)	2		Mean Difference (IV, Random, 95% CI)	Subtotals only
4.1 Postoperative creatinine change (µmol/L)	2	113	Mean Difference (IV, Random, 95% CI)	‐6.96 [‐27.42, 13.50]
4.2 Postoperative day 1 creatinine change (µmol/L)	2	113	Mean Difference (IV, Random, 95% CI)	4.94 [‐5.91, 15.78]
5 Postoperative creatinine (µmol/L)	7		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
5.1 Postoperative creatinine	3	235	Mean Difference (IV, Fixed, 95% CI)	‐1.31 [‐9.30, 6.68]
5.2 Postoperative day 1 creatinine	3	211	Mean Difference (IV, Fixed, 95% CI)	‐6.26 [‐21.17, 8.64]
5.3 Postoperative day 3 creatinine	4	301	Mean Difference (IV, Fixed, 95% CI)	‐0.47 [‐30.12, 29.19]
5.4 Postoperative week 1 creatinine	4	309	Mean Difference (IV, Fixed, 95% CI)	‐5.36 [‐25.29, 14.56]
6 Postoperative creatinine clearance (mL/min)	3	222	Mean Difference (IV, Fixed, 95% CI)	12.61 [‐2.31, 27.54]
7 PaCO2 (mmHg)	7		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
7.1 Postoperative PaCO2	7	446	Mean Difference (IV, Fixed, 95% CI)	1.05 [0.15, 1.94]
7.2 Postoperative day 1 PaCO2	2	91	Mean Difference (IV, Fixed, 95% CI)	3.33 [2.03, 4.64]
8 Postoperative nausea and vomiting	3	168	Odds Ratio (M‐H, Fixed, 95% CI)	0.66 [0.34, 1.30]
9 Intraoperative blood loss (mL)	11		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
9.1 Intraoperative blood loss < 1000 mL	5	202	Mean Difference (IV, Fixed, 95% CI)	5.90 [‐45.18, 56.99]
9.2 Intraoperative blood loss ≥ 1000 mL	6	374	Mean Difference (IV, Fixed, 95% CI)	‐173.07 [‐438.83, 92.68]
10 Intraoperative red cell transfusion	4	152	Mean Difference (IV, Fixed, 95% CI)	‐29.10 [‐117.03, 58.84]
11 Intraoperative transfusion ‐ other products (log values)	4		Mean Difference (Fixed, 95% CI)	Subtotals only
11.1 Platelet transfusion (Higgins 3)	4		Mean Difference (Fixed, 95% CI)	1.23 [0.22, 2.25]
11.2 Fresh frozen plasma transfusion (Higgins 3)	3		Mean Difference (Fixed, 95% CI)	0.47 [‐0.37, 1.30]
12 Variables of coagulation ‐ activated partial thromboplastin time (s)	2	181	Mean Difference (IV, Fixed, 95% CI)	0.88 [‐1.82, 3.58]
13 Variables of coagulation ‐ other	2		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
13.1 Factor VIII (IU/L)	2	181	Mean Difference (IV, Fixed, 95% CI)	‐29.54 [‐46.16, ‐12.91]
13.2 von Willebrand factor (IU/L)	2	181	Mean Difference (IV, Fixed, 95% CI)	‐31.39 [‐47.71, ‐15.06]
14 Plasma pH	12		Mean Difference (IV, Random, 95% CI)	Subtotals only
14.1 Postoperative pH	12	720	Mean Difference (IV, Random, 95% CI)	0.05 [0.04, 0.07]
14.2 Postoperative day 1 pH	2	91	Mean Difference (IV, Random, 95% CI)	0.01 [‐0.00, 0.03]
15 Base excess (mmol/L)	9		Mean Difference (IV, Random, 95% CI)	Subtotals only
15.1 Postoperative base excess	9	459	Mean Difference (IV, Random, 95% CI)	3.51 [2.61, 4.41]
15.2 Postoperative day 1 base excess	3	138	Mean Difference (IV, Random, 95% CI)	2.48 [1.61, 3.36]
16 Serum bicarbonate (mmol/L)	8	478	Mean Difference (IV, Random, 95% CI)	3.14 [2.30, 3.98]
17 Serum glucose (mmol/L)	3	145	Mean Difference (IV, Fixed, 95% CI)	‐0.00 [‐0.29, 0.29]
18 Serum chloride (mmol/L)	11		Mean Difference (IV, Random, 95% CI)	Subtotals only
18.1 Postoperative chloride	10	530	Mean Difference (IV, Random, 95% CI)	‐6.77 [‐10.17, ‐3.38]
18.2 Postoperative day 1 chloride	5	258	Mean Difference (IV, Random, 95% CI)	‐8.48 [‐15.88, ‐1.08]
19 Serum potassium (mmol/L)	7	459	Mean Difference (IV, Fixed, 95% CI)	‐0.04 [‐0.14, 0.06]
20 Serum sodium (mmol/L)	8		Mean Difference (IV, Fixed, 95% CI)	Subtotals only
20.1 Postoperative sodium	8	474	Mean Difference (IV, Fixed, 95% CI)	‐2.26 [‐2.84, ‐1.68]
20.2 Postoperative day 1 sodium	2	91	Mean Difference (IV, Fixed, 95% CI)	‐1.22 [‐2.55, 0.12]
21 Serum lactate (mmol/L)	4	224	Mean Difference (IV, Random, 95% CI)	0.52 [‐0.04, 1.08]
22 Postoperative length of hospital stay (days)	5	348	Mean Difference (IV, Fixed, 95% CI)	0.37 [‐0.72, 1.47]