Chen 2011.

Methods	RCT, 60 participants were randomly divided into 2 groups, with 30 participants in each group Participants in Group I were treated with 2 g propacetamol 15 min before the end of operation
Participants	Type of surgery: lumbar spine surgery Propacetamol group Entered/completing: 30 Age (mean, SD): 48, 13 Sex (male, %): 13, 43% Control group Entered/completing: 30 Age (mean, SD): 53, 14 Sex (male, %): 14, 47%
Interventions	2 g propacetamol in 100 ml saline, intravenous injection, 15 min before the end of operation Placebo: 100 ml saline, intravenous injection, 15 min before the end of operation
Outcomes	The authors did not point out which were primary outcomes Vomiting frequency in 48 h after the operation VAS pain score (0 to 10), Ramsay sedation score(0, 1, 2, 3), breathing frequency, heart rate and mean arterial pressure were observed at the time of 0 min, 30 min, 1 h, 2 h, 4 h, 6 h, 12 h, 24 h, 36 h, 48 h after the operation
Source of funding	Not reported
Were treatment groups comparable at baseline?	Yes: sex, age, weight, height
Details of preoperative pain	Not reported
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details reported
Allocation concealment (selection bias)	Unclear risk	Not mentioned
Blinding (performance bias and detection bias) All outcomes	Unclear risk	Not mentioned
Incomplete outcome data (attrition bias) All outcomes	Low risk	Reported as no incomplete outcome data in the study
Selective reporting (reporting bias)	High risk	There were only comparisons of VAS pain scores and Ramsay sedation scores between the 2 groups as shown in Table 2 and 3
Size	High risk	Fewer than 50 participants per arm of the study (30 propacetamol, 30 placebo)