Scheinin 1982.

Methods	RCT Informed consent obtained Setting: Finland Funding: unspecified
Participants	40 ASA 1 to 3 patients undergoing upper abdominal surgery
Interventions	Treatment group: thoracic (catheter tip at T9‐T10) epidural with 2 injections of 10 mL of bupivacaine 0.5% at 4 hours apart (n = 10) Control group: epidural with 2 (n = 10) or 4 mg of morphine (n = 10)
Outcomes	Pain at 4 hours after anaesthesia
Notes	No outcomes of interest available for our selected time points Study also includes a group without epidural
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"randomly allocated", no details
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	Low risk	"treated double‐blind: the anaesthetist performing the epidural injection was unaware of which drug or dose was injected"
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Study authors did not specify the identity of the outcome assessor
Incomplete outcome data (attrition bias) All outcomes	Low risk	No loss to follow‐up
Selective reporting (reporting bias)	Low risk	All results reported
Other bias	High risk	A considerable difference in duration of surgery was noted among groups. Participants' demographics (such as age and ASA) were not fully reported, so we cannot evaluate whether the backgrounds of participants were well balanced