Sakaida 1998.

Methods	Parallel‐group randomized controlled trial, conducted in Japan. Study dates not reported
Participants	40 elective coronary artery bypass graft, mitral valve or aortic valve replacement surgery patients
Interventions	Low‐dose opioid (mean fentanyl 7.6 ± 1.6 μg/kg and isoflurane/nitrous oxide) in 20 participants High‐dose opioid (mean fentanyl 99 ± 5.8 μg/kg and nitrous oxide) in 20 participants Details of who decided when to extubate were not given.
Outcomes	Time to extubation Length of stay in the ICU Length of stay in hospital
Notes	Japanese article. No power calculation was done. No details about funding source were given. Details of any declarations of conflict of interest among study authors were not provided.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details given
Allocation concealment (selection bias)	Unclear risk	No details given
Blinding (performance bias and detection bias) All outcomes	Unclear risk	No details given
Incomplete outcome data (attrition bias) All outcomes	Low risk	No withdrawal from the study
Selective reporting (reporting bias)	High risk	Mortality and postoperative complications not reported
Other bias	Low risk	Preoperative and intraoperative characteristics were similar in the 2 groups: age, sex, height, weight, body surface area, ejection fraction, duration of surgery, duration of anaesthesia, CPB duration and aortic clamping time.