Limoges 2004.

Study characteristics
Methods	Type of study: double blind, placebo‐controlled, parallel RCT. Condition and number of participants randomised: participants undergoing screening flexible sigmoidoscopy (N = 90). Groups: TENS group (N = 30); placebo TENS group (N = 30); control group (N = 30).
Participants	Demographics: N = 90, 51 male/39 female. TENS group, 57.18 ± 7.787 yrs; placebo TENS group, 55.97 ± 5.411 yrs; control group, 58.6 ± 9.073 yrs (mean ± SD). Setting:  screening flexible sigmoidoscopy (SFS) speciality clinic. Inclusion: over 50 yrs; presenting for screening flexible sigmoidoscopy. Exclusion: cardiac pacemakers; automated implanted cardiac defibrillators; pre procedural skin irritation at electrode placement site; pre procedural sedation or analgesia. Withdrawals/dropouts: not detailed.
Interventions	Where applied: in clinic. Applied by: clinician. Waveform: biphasic waveform and asymmetric pulse pattern. Frequency: 100 Hz. Pulse duration: 190 μs. Pulse amplitude/Intensity: 30 mA, setting chosen after progressively increasing amplitude and testing tolerability of each level on volunteers. Same intensity used for all participants. Placebo TENS Group: unit same as active group, attached to participant but not turned on. All participants told they may or may not feel tingling sensation at electrode site. Control Group: received only verbal encouragement. Electrodes: 4 self‐adhesive, 2 x 5 inch rectangular, 2 on left upper and lower quadrants of abdomen and 2 parallel to spinal cord at L1‐S3 level. Duration and frequency of Rx: varied 5 to 15 mins, 1 Rx. Device/manufacturer: Empi EPIX VT TENS. Adverse effects: 29 participants in TENS group and 6 participants in placebo TENS group reported pain/burning/tingling at electrode site.
Outcomes	Pain outcome: pain experienced during procedure assessed by a NRS of 1 to 5 for pain intensity after procedure finished.  ITT/per protocol analysis: not detailed. Statistical analysis: no significant difference between groups for pain experienced during the procedure.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Author response: "Randomization was done by drawing numbers out of a hat. We picked a number out of the hat after the patient arrived and consented to participate".
Allocation concealment (selection bias)	High risk	Author response: "Randomization was done by drawing numbers out of a hat. We picked a number out of the hat after the patient arrived and consented to participate".
Incomplete outcome data (attrition bias) All outcomes	Low risk	"Ninety subjects were enrolled and completed the study".
Source of funding bias	Low risk	"Funding for this study was provided by the Innovative Pilot Project Grant Program at the University of California Davis Medical Center. The TENS unit was provided by EMPI, Inc."
Blinding (Participant)	High risk	It is impossible to adequately blind participants who receive electrical stimulation. "Subjects in the sham TENS group were connected to the TENS unit exactly the same as subjects in the TENS group. The research assistant manipulated the programming buttons on the TENS unit exactly as with the TENS group, but without actually turning the TENS units on beforehand. This step was performed in an effort to maintain blinding of both the endoscopist and subject. Subjects in the control group received only verbal encouragement." The inclusion/exclusion criteria did not state that participants had to be TENS naïve. Control group received no active treatment so these participants could not be blinded.
Blinding (Outcome Assessor)	High risk	Author response regarding the placebo TENS group: "the TENS unit was attached to the subject but never turned on by the RA (I and the subject were blinded to this)". "My RA administered the questionnaires".
Sample Size	High risk	TENS (N = 30); placebo TENS (N = 30); control (N = 30).