Wang 2000b.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: 2 groups, monoprophylaxis
Participants	Baseline characteristics Dexamethasone Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 45 Received treatment (n): NA Analysed (n): 41 Age (mean ± SD, median (IQR), median (range)): 32 (28 to 36) Weight (mean ± SD, median (IQR), median (range)): 54 (42 to 73) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA/NA/0/0 Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (isoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 68 Use of perioperative opioids (if yes, which?): 2 µg/kg fentanyl for induction Type of surgery: laparoscopic tubal ligation Placebo Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 45 Received treatment (n): NA Analysed (n): 40 Age (mean ± SD, median (IQR), median (range)): 34 (31 to 35) Weight (mean ± SD, median (IQR), median (range)): 56 (46 to 75) BMI (mean ± SD, median (IQR), median (range)): NA ASA I/II/III/IV (n): NA/NA/0/0 Gender (female in %): 100 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (isoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 65 Use of perioperative opioids (if yes, which?): 2 µg/kg fentanyl for induction Type of surgery: laparoscopic tubal ligation Included criteria: women, ASA I or II, scheduled for outpatient laparoscopic tubal ligation Excluded criteria: breastfeeding, weighing > 90 kg, taking any medication other than an oral contraceptive pill Pretreatment: baseline characteristics (age, weight, ASA): no. Potential effect modifiers (gender, duration of anaesthesia, perioperative opioids): no; (history of PONV/motion sickness, non‐smoker): unclear
Interventions	Intervention characteristics Dexamethasone Dose: 10 mg Time point of administration: at time of induction Route of administration: IV Rescue antiemetics (if yes, which?): (7%) ondansetron 4 mg IV Placebo Dose: 2 ml saline Time point of administration: at time of induction Route of administration: IV Rescue antiemetics (if yes, which?): (28%) ondansetron 4 mg IV
Outcomes	Vomiting (0 to 24 hours) Outcome type: dichotomous outcome Vomiting (0 to 4 hours) Outcome type: dichotomous outcome Vomiting (4 to 24 hours) Outcome type: dichotomous outcome Nausea (0 to 24 hours) Outcome type: dichotomous outcome
Identification	Sponsorship source: this work was supported in part by grant NSC89‐2314‐B‐016‐060 from the National Council of Science, Taiwan Country: Taiwan Setting: outpatient, single‐centre Author's name: J.J. Wang Institution: Department of Anesthesiology Tri‐Service General Hospital, National Defense Medical Center, Taipei, Taiwan Email: NA Address: Department of Anesthesiology, Tri‐Service General Hospital/National Defense Medical Center, No. 8, Sec. 3, Ting‐Chow Road, Taipei, Taiwan Language: English Duration of study: NA Trial registry number: NA Study's primary outcome: incidence of PONV
Notes	None
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "using a computer‐generated random number table"
Allocation concealment (selection bias)	Unclear risk	Judgement comment: no statement
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Quote: "both patient and investigator were blinded" Quote: "medications (2 ml) were prepared by one of the investigators" Judgement comment: no statement on blinding of anaesthesiologists (investigators = anaesthesiologists?)
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Quote: "both patient and investigator were blinded" Judgement comment: no information on who is doing the outcome assessment
Incomplete outcome data (attrition bias) All outcomes	Low risk	Quote: "patients enrolled in this study, six patients who did not complete the surgical procedure (laparoscopic tubal Discussion ligation) because of intra‐abdominal adhesions and three patients who could not be contacted by telephone after. Although the use of..."
Selective reporting (reporting bias)	Unclear risk	Judgement comment: no reference to a study protocol or trial registry number reported
Other bias	Unclear risk	Quote: "patient characteristics, interval since the the last menstrual period and the durations of anaesthesia and surgery were reported. In our study, we found that the total incidence of PONV was 73% within 24 h postoperatively in patients similar in the two groups (Table 1). There were no significant differences" Judgement comment: baseline characteristics (age, weight, ASA): no. Potential effect modifiers (gender, duration of anaesthesia, perioperative opioids): no; (history of PONV/motion sickness, non‐smoker): unclear