Seeling 1990a.

Methods	RCT Setting: Germany Funding: unspecified
Participants	75 participants undergoing major abdominal surgery
Interventions	Treatment group: thoracic epidural analgesia started after surgery with bupivacaine 0.5% for the first bolus and 0.25% for subsequent doses given as 0.15 mL/kg every 2 hours, until 19H00 the day after surgery (n = 15) Control group: IV buprenorphine (n = 16) General anaesthesia for all participants
Outcomes	Pain at rest and on coughing at 24 hours after surgery
Notes	Study also includes 2 other groups: Group III: buprenorphine given epidurally. This group was not retained, as something other than just local anaesthetic, opioid or epinephrine, was injected epidurally Group IV: bupivacaine plus buprenorphine given epidurally, also excluded
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomly divided"
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Not mentioned
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not mentioned
Incomplete outcome data (attrition bias) All outcomes	High risk	Owing to technical problems, 11 participants were withdrawn from the study: insufficient epidural extension (n = 4); inability to deal with the pain scale (n = 2); operative and postoperative complications (n = 4); other (n = 1). Their specific group allocation is not mentioned
Selective reporting (reporting bias)	Low risk	All results reported
Other bias	Unclear risk	Not in intention‐to‐treat