Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomization tables (one for each institution and stratified for the surgical site)
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias)	High risk	Double‐blinding of the type of solution in the epidural
Blinding of outcome assessment (detection bias)	High risk	Double‐blinding of the type of solution in the epidural
Incomplete outcome data (attrition bias)	High risk	Two participants withdrawn because the epidural could not be inserted
Selective reporting (reporting bias)	High risk	Not in intention‐to‐treat analysis
Other bias	Low risk	Groups well balanced for age and underlying pathology