Heidari 2011.

Methods	Design: randomized double‐blinded controlled trial Withdrawals: none Setting: single centre in the Middle East Sample size: 90; 3 groups within the trial
Participants	Age (mean): 43.6/40.9 years Gender (M/F): 28/32 ASA grade: I to II Surgery type: elective lower abdominal surgery Surgery duration (mean): 1.3/1.5 hours Anaesthesia type: general One arm consisted of participants who received a fluid formulation that was not relevant to this review. Details for this arm of the study are not extracted here.
Interventions	Intervention n = 30 Buffered arm ‐ Ringer's lactate 15 mL/kg administered 30 minutes preoperatively Control n = 30 Non‐buffered arm ‐ normal saline 15 mL/kg administered 30 minutes preoperatively Co‐interventions: none
Outcomes	Postoperative nausea using VAS and incidence of postoperative vomiting at 6, 12, and 24 hours postoperatively
Notes	Funding source: not disclosed Declarations of interest: none disclosed
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Allocated randomly according to random number table
Allocation concealment (selection bias)	Unclear risk	Not described
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Reported as 'double‐blinded' but blinding methods not described
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Reported as 'double‐blinded' but blinding methods not described
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	No participants lost to follow‐up
Selective reporting (reporting bias)	Low risk	No evidence of selection bias. All proposed outcome measures adequately reported
Other bias	Unclear risk	Type of surgery not described in detail