Engoren 1998.

Methods	Parallel‐group randomized controlled trial, conducted in the United States. Study dates not reported
Participants	70 patients undergoing primary coronary artery bypass surgery. Excluded were those with concomitant valve, carotid artery or other co‐incident surgery.
Interventions	Low‐dose opioid (isoflurane anaesthesia with a continuous infusion of propofol and mean fentanyl dose 13.7 μg/kg) in 35 participants High‐dose opioid (isoflurane anaesthesia and mean fentanyl dose 21.0 μg/kg) in 35 participants Details of who decided when to extubate were not given in the paper.
Outcomes	Risk of mortality in hospital Risk of myocardial infarction Risk of stroke Risk of tracheal reintubation Time to extubation Length of stay in the ICU Length of stay in hospital Cost of anaesthesia drugs
Notes	Weaning protocol was the same in both groups, but timing was different, as described in the paper. Power calculation was performed. 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)	Low risk	"Patients were randomized by a computer‐generated scheme"
Allocation concealment (selection bias)	High risk	"..and the anaesthesia provider was informed of the assignment while preparing the room for anaesthesia"
Blinding (performance bias and detection bias) All outcomes	Unclear risk	"..and the anaesthesia provider was informed of the assignment while preparing the room for anaesthesia"
Incomplete outcome data (attrition bias) All outcomes	Low risk	No participants withdrew from the study.
Selective reporting (reporting bias)	Low risk	All collected outcomes reported
Other bias	Low risk	"Patients were very similar in baseline demographics (Table 1), although anaesthesia and cardiopulmonary bypass times were slightly longer in the propofol group"