Hu 2006.

Study characteristics
Methods	Parallel, 72 h
Participants	PCA 40, control 40 (third group receiving epidural analgesia not reported here) Lower abdominal surgery
Interventions	PCA: morphine. Bolus/lockout/4 h limit: 1 mg/6 to 8 min/25 mg Control: IM meperidine ‐ regimen not reported
Outcomes	Pain intensity at rest and with coughing, opioid use, interleukin‐1 and interleukin‐6 levels
Source of funding	Not reported
Notes	Chinese language journal QS = 2 (R = 1, DB = 0, W = 1)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding of participants and personnel (performance bias) All outcomes	High risk	Not blinded
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants completed the study
Selective reporting (reporting bias)	Low risk	All outcomes described in Methods section are reported in Results section.
Other bias	Unclear risk	Small sample size