Gilani 2008.

Methods	Single‐centre RCT
Participants	Setting: King Fahad National Guard Hospital, Saudi Arabia Inclusion criteria: patients above age of 18 years undergoing various elective and emergency surgical procedures under general anaesthesia Exclusion criteria: patients undergoing cardiac surgery or thoracic surgery Participant numbers: 200 randomly assigned; 200 analysed
Interventions	Intervention: general anaesthesia was maintained by 40% oxygen (FiO2 0.4) with nitrous oxide and volatile anaesthetic sevoflurane (MAC 1.2‐1.3) through oral endotracheal tube or laryngeal mask depending on the type of surgery. All patients received standard anaesthetic care and monitoring. Control: general anaesthesia was maintained by 40% oxygen (FiO2 0.4) with air and volatile anaesthetic sevoflurane (MAC 1.2‐1.3) through oral endotracheal tube or laryngeal mask depending on the type of surgery. All patients received standard anaesthetic care and monitoring.
Outcomes	Other outcomes: Postoperative pain
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Described as randomized but no further details.
Allocation concealment (selection bias)	Unclear risk	No details given.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	This was not reported.
Blinding of outcome assessment (detection bias) Inhospital case fatality rate/length of stay	Unclear risk	—
Blinding of outcome assessment (detection bias) Complications	Unclear risk	This was not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No missing data.
Selective reporting (reporting bias)	Low risk	All outcomes described in methods section reported.
Other bias	Low risk	No other potential sources of bias were detected.