Demirhan 2013.

Study characteristics
Methods	Study design: randomized controlled trial Study grouping: 2 groups, monoprophylaxis
Participants	Baseline characteristics Placebo (group P) Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 20 Received treatment (n): 20 Analysed (n): 20 Age (mean ± SD, median (IQR), median (range)): 27.7 ± 8.3 Weight (mean ± SD, median (IQR), median (range)): NA BMI (mean ± SD, median (IQR), median (range)): 23.6 ± 3.1 ASA I/II/III/IV (n): 13/7/0/0 Gender (female in %): 40 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (N₂O, sevoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 86.1 Use of perioperative opioids (if yes, which?): 580 µg remifentanil, 50 mg tramadol, 20% of patients needed pethidine Type of surgery: elective rhinoplasty Dexamethasone (group PD) Assessed for eligibility (n): ‐ Enrolled (n): ‐ Randomized (n): 20 Received treatment (n): 20 Analysed (n): 20 Age (mean ± SD, median (IQR), median (range)): 26.5 ± 8.9 Weight (mean ± SD, median (IQR), median (range)): NA BMI (mean ± SD, median (IQR), median (range)): 24.1 ± 3.0 ASA I/II/III/IV (n): 14/6/0/0 Gender (female in %): 25 Non‐smoker (%): NA History of PONV/motion sickness (%): NA Type of general anaesthesia: inhalational anaesthesia (N₂O, sevoflurane) Duration of anaesthesia or surgery (in min; as mean or median): 81.3 Use of perioperative opioids (if yes, which?): 660 µg remifentanil, 20 mg tramadol, 5% of patients needed pethidine Type of surgery: elective rhinoplasty Included criteria: ASA I and II, 18 to 75 years of age, waiting for elective rhinoplasty Excluded criteria: insufficient cooperation (e.g. psychiatric disorder, dementia); regular use of drugs (benzodiazepines, corticosteroids, tricyclic antidepressants, NSAIDs, or other analgesic drugs); preoperative current use of pregabalin or gabapentin; history of allergy to any of the study medications; pregnancy; obesity (body mass index > 35 kg/m²); significant cardiac, pulmonary, hepatic, or renal disease Pretreatment: baseline characteristics (age, BMI, ASA): no. Potential effect modifiers (gender, duration of anaesthesia): no; (history of PONV/motion sickness, non‐smoker): unclear; (perioperative opioids): yes
Interventions	Intervention characteristics Placebo (group P) Dose: saline Time point of administration: after induction of anaesthesia Route of administration: IV Rescue antiemetics (if yes, which?): 20% (ondansetron 4 mg IV) Dexamethasone (group PD) Dose: 8 mg Time point of administration: after induction of anaesthesia Route of administration: IV Rescue antiemetics (if yes, which?): 30% (ondansetron 4 mg IV)
Outcomes	Vomiting (0 to 24 hours) Outcome type: dichotomous outcome Vomiting (0 to 2 hours) Outcome type: dichotomous outcome Nausea (0 to 24 hours) Outcome type: dichotomous outcome Headache (0 to 24 hours) Outcome type: dichotomous outcome Visual disturbances (e.g. blurred vision) (0 to 24 hours) Outcome type: dichotomous outcome Adverse events (general notes in the publication, 24 hours' observation) Outcome type: general notes on side effects
Identification	Sponsorship source: NA Country: Turkey Setting: inpatient, single‐centre Author's name: Abdullah Demirhan Institution: Department of Anesthesiology and Reanimation, Abant Izzet Baysal University Medical School, Golkoy, Bolu, Turkey Email: dr_demirhan1@hotmail.com Address: Department of Anesthesiology and Reanimation, Abant Izzet Baysal University Medical School, Golkoy, 14280 Bolu, Turkey Duration of study: NA Language: English Study's primary outcome: NA Trial registry number: NA
Notes	Two out of 3 groups relevant (co‐administration of pregabalin in both groups)
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "computer‐generated list of random numbers"
Allocation concealment (selection bias)	Unclear risk	Judgement comment: no statement
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: "by the same researcher who was not involved in the intraoperative or postoperative treatment and data collection" Quote: "...P and PD, and a similar‐looking placebo capsule was given to the controls (Group C) by the same researcher who was not involved in the intraoperative or postoperative treatment and data collection. The exact same packaging was used for the placebo capsules as the active capsules. In the operating room, intravenous..."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "the NRS values were recorded at 30 min and 1 h in the PACU and at 2, 4, 8, 12, and 24 h in the inpatient unit by the same researcher who was totally unaware of the patient groups"
Incomplete outcome data (attrition bias) All outcomes	Low risk	Judgement comment: no missing outcome data
Selective reporting (reporting bias)	Unclear risk	Judgement comment: no reference to a study protocol or trial registry number reported
Other bias	High risk	Quote: "Group P and Group PD exhibited statistically significant lower tramadol consumption compared to Group C within the 0–24‐h postoperative period (p \ 0.01 for all). There was a statistically significant difference between Group P and Group PD with respect to tramadol consumption (p = 0.016) only in the first 1‐h period. Table 2 and Fig. 1 give the mean tramadol consumption (mg) of the groups within the first 24‐h period" Judgement comment: baseline characteristics (age, BMI, ASA): no. Potential effect modifiers (gender, duration of anaesthesia): no; (history of PONV/motion sickness, non‐smoker): unclear; (perioperative opioids): yes