Abstract: We included 12 trials in the original review (2009) and included no further trials in the first update (2011). An additional seven new trials met the inclusion criteria in this second update. In total, we included 19 RCTs involving 1346 participants at entry, with 11 trials awaiting classification either because the full text was unavailable or information in the full text failed to clarify eligibility. We excluded most trials because TENS was given in combination with another treatment as part of the formal study design or TENS was not delivered using appropriate TENS technique. The types of acute pain included in this Cochrane Review were procedural pain, e.g. cervical laser treatment, venepuncture, screening flexible sigmoidoscopy and non-procedural pain, e.g. postpartum uterine contractions and rib fractures. We pooled data for pain intensity for six trials (seven comparisons) comparing TENS with placebo but the I2 statistic suggested substantial heterogeneity. Mean difference (MD) with 95% confidence intervals (CIs) on a visual analogue scale (VAS, 100 mm) was -24.62 mm (95% CI -31.79 to -17.46) in favour of TENS. Data for the proportion of participants achieving ≥ 50% reduction in pain was pooled for four trials (seven comparisons) and relative risk was 3.91 (95% CI 2.42 to 6.32) in favour of TENS over placebo. We pooled data for pain intensity from five trials (seven comparisons) but the I2 statistic suggested considerable heterogeneity. MD was -19.05 mm (95% CI -27.30 to -10.79) in favour of TENS using a random-effects model. It was not possible to pool other data. There was a high risk of bias associated with inadequate sample sizes in treatment arms and unsuccessful blinding of treatment interventions. Seven trials reported minor adverse effects, such as mild erythema and itching underneath the electrodes and participants disliking TENS sensation. This Cochrane Review update includes seven new trials, in addition to the 12 trials reviewed in the first update in 2011. The analysis provides tentative evidence that TENS reduces pain intensity over and above that seen with placebo (no current) TENS when administered as a stand-alone treatment for acute pain in adults. The high risk of bias associated with inadequate sample sizes in treatment arms and unsuccessful blinding of treatment interventions makes definitive conclusions impossible. There was incomplete reporting of treatment in many reports making replication of trials impossible.

Plain-language summary: We included 19 clinical trials published up to 3 December 2014, which examined 1346 people. The trials administered TENS to produce a strong non painful 'tingling' sensation at the site of acute pain. The trials assessed TENS for cervical laser treatment, venepuncture, sigmoidoscopy, rib fractures and uterine contractions after childbirth. We did not include trials that assessed TENS for pain associated with childbirth, dental procedures and menstruation because they have been the subject of other Cochrane Reviews. Eleven trials are awaiting classification. TENS was better than placebo TENS (delivering no electrical current) at reducing the intensity of acute pain but the reduction in pain was not consistent across all trials. This finding was based on an analysis of only six of the 19 trials. There was an insufficient number patients to make a firm conclusion. A small number of patients experienced itching and redness beneath the TENS pads or disliked the sensation produced by TENS. Overall we concluded that TENS may reduce the intensity of acute pain in some patients but the quality of evidence was weak. TENS is inexpensive, safe and can be self-administered. We recommended that TENS should be considered as a treatment option given on its own or in combination with other treatments. The quality of the evidence was moderate to low because sample sizes were small and some patients were aware that they were receiving TENS or placebo.