Methods	RCT, 2-arm parallel group design.
Participants	Setting: hospital in Surrey, UK. 17 healthy women 36-40 weeks’ gestation requesting pethidine for pain relief in labour, ASA I or II. Women with a contraindication to pethidine or remifentanil or requesting epidural were excluded
Interventions	Experimental: IV PCA remifentanil, 0.5 mcg bolus per kg (based on antenatal booking weight) with 2 min lock-out, no hourly max Control: IV PCA pethidine, 10 mg bolus, 5 min lock-out, 100 mg hourly max All women were given 10 mg metoclopramide IV over 8 hrs.
Outcomes	Maternal: pain on 10 cm VAS recorded hourly; nausea recorded on a 10 cm VAS; itching; BP pulse and resps Neonate: 1 and 5 min Apgar scores.
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described “randomly allocated”.
Allocation concealment (selection bias)	Low risk	“by selecting the next in a series of sealed envelopes prepared by pharmacy.”
Blinding (performance bias and detection bias) Women	Low risk	Women were described as blind.
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	“One investigator selected the envelope and prepared the PCA pump. the pump was covered so that the other investigator, the observer, was unable to see which drug the woman was receiving.”
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	See above.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No loss to follow-up apparent although for some outcomes it was not clear what the denominators were
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Low risk	None apparent.