Kim 2012.

Study characteristics
Methods	Type of study: single‐blind, placebo‐controlled RCT. Condition and number of participants randomised: 100 patients undergoing plastic surgery. Groups: 2 groups: active TENS (N = 50); placebo TENS (N = 50).
Participants	Demographics: N = 100; TENS group 21 male/29 female; age 48.2 yrs ± 13.0; placebo group 19 male/31 female; age 51.2 yrs ± 11.7. Setting: Hospital outpatient, Korea. Inclusion: patients undergoing plastic surgery. Exclusion: concomitant sedative or analgesic medication and neurological disease, or potentially serious internal diseases (ASA physical status > 3). Withdrawals/dropouts: none.
Interventions	Where applied: radial side of the dominant forearm ‐ cathode over cephalic vein 1cm proximal to radial styloid process; anode 3 cm away proximal to cathode. Applied by: anaesthesiologist. Waveform: not stated. Frequency: 80Hz. Pulse duration: 200 μs. Pulse amplitude/Intensity: maximum tolerable level below pain threshold without noticeable muscle contraction. Placebo TENS Group: TENS device without current output but with power indicator light illuminated. Control Group: none. Electrodes: 2 TensCare electrodes, 5 cm² Duration and frequency of Rx: 20 minutes immediately prior to venous cannulation. 1 single Rx. Device/manufacturer: select TENS unit (Empi, St Paul, Minnesota). Adverse effects: itching and erythema reported.
Outcomes	Pain outcome: pain incidence; VAS scores. ITT/per protocol analysis: not stated. Statistical analysis: pain incidence was similar between the 2 groups (P > 0.05); 45 (90%) in the TENS group experienced pain against 50 (100%) in the placebo group using the X² test or Fisher exact test. Pain intensity (VAS) in TENS group was significantly lower than placebo, with TENS VAS scores 1.9 ± 1.2 (P < 0.01) against placebo VAS scores 4.8 ± 1.5 using Wlcoxon rank sum test with continuity correction.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	No details provided.
Allocation concealment (selection bias)	Unclear risk	No details provided.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Not stated but no withdrawals/dropouts reported.
Source of funding bias	Low risk	No apparent funding bias.
Blinding (Participant)	Low risk	Placebo tens applied to blind participants.
Blinding (Outcome Assessor)	Low risk	"study‐blinded anaesthesiologist".
Sample Size	Unclear risk	TENS (N = 50); placebo TENS (N = 50).