Frey 2009b.

Methods	Parallel 4‐arm randomized trial (single centre) conducted in Germany. Study dates not reported.
Participants	229 patients, aged more than 18 years with ASA physical status I to III, undergoing laparoscopic cholecystectomy. Exclusion criteria were patients with cardiac pacemaker or implanted cardioverter/defibrillator, at risk of malignant hyperthermia, with allergy to nickel/chrome or change in surgical technique.
Interventions	Group 1: Acustimulation (ReliefBand) before induction of anaesthesia at P6 acupoint on dominant forearm for 24 h after surgery (n = 59). Group 2: Acu‐stimulation (ReliefBand) after induction of anaesthesia at P6 acupoint on dominant forearm for 24 h after surgery (n = 53). Group 3: Sham acustimulation (inactivated ReliefBand electrodes with a silicone cover) before induction of anaesthesia at P6 acupoint on dominant forearm for 24 h after surgery (n = 59) Group 4: Sham acustimulation (inactivated ReliefBand electrodes with a silicone cover) after induction of anaesthesia at P6 acupoint on dominant forearm for 24 h after surgery (n = 58).
Outcomes	Nausea (0 ‐ 2 h), vomiting (0 ‐ 2 h), rescue antiemetic (tropisetron 2 mg), side effects of ReliefBand (skin irritation under electrodes).
Notes	Combined Groups 1 and 2 as acustimulation group, and Groups 3 and 4 as sham group for analysis. No cumulative incidence of 0 ‐ 24 h outcomes reported. No details about funding source or any declarations of interest among authors.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Insufficient details.
Allocation concealment (selection bias)	Unclear risk	Participants randomized by "drawing a sealed envelope indicating treatment assignment." No details about envelopes being opaque.
Blinding of patients (performance bias) All outcomes	Low risk	Authors made efforts to inactivate electrodes and place a silicone cover over the device which "was invisible for both patients and investigators."
Blinding of healthcare providers (performance bias) All outcomes	Low risk	Authors made efforts to inactivate electrodes and place a silicone cover over the device which "was invisible for both patients and investigators."
Blinding of outcome assessor (detection bias) All outcomes	Low risk	"Patients were evaluated for the occurrence of nausea, retching, vomiting, pain and potential side effects of ReliefBand (skin irritation under the electrodes) by an investigator unaware of the patients' group assignment."
Incomplete outcome data (attrition bias) All outcomes	Low risk	29 did not receive allocated intervention because of change of surgical technique. No missing data reported for the 200 participants analysed.
Selective reporting (reporting bias)	Low risk	All expected outcomes reported. Authors stated "the requirement for rescue medication did not differ significantly between the treatment groups."
Other bias	Low risk	"The demographic and morphometric characteristics and factors likely to influence PONV were not significantly different in the acu‐stimulation and sham groups as were intraoperative variables."