Transcutaneous Electrical Nerve Stimulation (TENS) for Postoperative Pain Relief

Original Editor - Aminat Abolade

Top Contributors - Aminat Abolade, Kim Jackson and Leana Louw  

Introduction

Conventional approaches to the management of post-operative pain remains inadequate. Intermittent ‘on-demand’ administration of opiates results in fluctuating plasma levels and poor pain relief; increasing the frequency of administration and the amount of opiate may improve pain control but results in unwanted side effects. Intravenous opiate infusion may provide better analgesia but with the risk of respiratory depression.

The success of Transcutaneous Electrical Stimulation in the management of chronic pain along with its absence of side effects, particularly respiratory depression, has led to its recent use in the management of post-operative pain. Transcutaneous Electrical Nerve stimulation (TENS) is an effective adjunctive therapy for postoperative pain; however, effects of different frequencies of stimulation have not been systematically investigated.

Description

Transcutaneous Electrical Nerve Stimulation (TENS) is a non-pharmacologic strategy that is used to treat postoperative pain during cardiac operations,cholecystectomy,cesarean delivery, and thoracotomy. Further, in a systematic review,' Bjordal and colleagues' showed decreases in analgesic consumption in patients using TENS postoperatively. In addition, treatment with TENS results in a lower incidence of postoperative complications, such as paralytic ileum and atelectasis, and improves pulmonary function. However, some surgical procedures seem to be too painful for TENS to have a significant effect on the pain, as an example, posterior thoracotomy results in severe postoperative pain that is unaffected by TENS.

Transcutaneous Electrical Nerve Stimulation (TENS) has been used as a complementary therapeutic option to control chronic and acute pain of various procedures such as abdominal and thoracic surgeries since 1970. One of the mechanisms of the analgesia produced by TENS was described by Melzak and Wall (1967) in the mid-1960s. It is based on the Gate Control theory of pain, in which the modulation of pain results from the activation of descending inhibitory pathways. TENS is a safe and simple method whose daily repeated application produces analgesic tolerance at spinal opioid receptors and increases the toleration threshold of pain. Also, TENS leads to the release of endorphins and serotonin and analgesic hormones and reduction of cytokine levels. Furthermore, electrical stimulation indirectly improves muscle spasm by increasing blood flow to muscle tissue. In the 2015 study by Galli, Chiavegato, and Liebano conducted on 74 kidney donors, patients in TENS group had significantly lower pain during respiratory maneuvers and higher maximal expiratory pressure compared with the control group. In another study, Fiorelli et al. (2012) applied TENS after thoracotomy for 5 consecutive days and found that pulmonary function (forced expiratory volume in 1 second [FEV1] to forced volume capacity [FVC] ratio) was significantly better and blood cytokine levels and narcotic consumption were significantly lower in the TENS group than the placebo group. In addition to the pain relief action of TENS, Unterrainer et al. (2010) reported the effectiveness of TENS in improving cognitive functions in patients undergoing spinal surgery.

Hence, simultaneous use of TENS with pharmacologic therapies for analgesia should produce a greater reduction in postoperative pain and a concomitantly decreasing medicine intake, reducing side effects, and improving treatment for pain.

Studies in Postoperative Rehabilitation

Transcutaneous Electrical Nerve Stimulation (TENS) has been used extensively to control postoperative pain, but its effects are controversial. This is probably due to the different types of operations performed and, therefore, to the varying intensity of postoperative pain. Here we present an extensive study with TENS in 324 patients who underwent different types of thoracic surgical procedures: posterolateral thoracotomy, muscle-sparing thoracotomy, costotomy, sternotomy, and video-assisted thoracoscopy. Each patient cohort was randomly subdivided into three treatment groups: TENS, placebo TENS and control. The effectiveness of TENS was assessed by two factors: the time from the beginning of treatment to the request for further analgesia and the total medication intake during the first 12 hours after operation.Whereas posterolateral thoracotomy produced severe pain, muscle-sparing thoracotomy, costotomy, and sternotomy caused moderate pain, and video-assisted thoracoscopy caused only mild pain. The TENS treatment was not effective in the posterolateral thoracotomy group, but it was useful as an adjunct to other medications in the muscle-sparing thoracotomy, costotomy, and sternotomy groups. In contrast, representing the only pain control treatment with no adjunct drugs, it was very effective in patients having video-assisted thoracoscopy. Conclusions from these findings show that TENS is useful after thoracic surgical procedures only when postoperative pain is mild to moderate; it is uneffective for severe pain.

Another study carried out on the effects of Transcutaneous Electrical Nerve Stimulation (TENS) on acute postoperative pain intensity and mobility after Hip Fracture showed that addition of TENS to the standard care of elderly patients in the early days following Gamma nail surgical fixation of extracapsular hip fracture is recommended for pain management while walking and functional gait recovery and the effect of TENS on long-term functional outcomes should be explored in future studies. The standard rehabilitation care included five daily 30 minutes physical therapy treatments beginning 24 hours after surgery. Outcome measures were: pain intensity at rest, at night and during ambulation (assessed with the Numeric Rating Scale; Functional Ambulation Classification instrument; time to complete five sit-to-stand tests; and two-minute walk test). Data were analysed with Wilcoxon score rank tests. Significance was set at p≤0.05. Results showed significant greater pain reduction during walking was noted in the active TENS group compared to sham TENS group. Additionally, advantage of active TENS was demonstrated in greater increase in walking distance on the fifth day and higher level of mobility compared to the sham TENS group. No additional effects of active TENS were noted on pain intensity at rest and at night and on five times sit-to-stand performance.

Current use in physiotherapy

The widespread availability of TENS for use in physiotherapy has been well documented. In a survey carried out of 139 National Health Service hospitals in England with a response rate of 83.5%, TENS was identified as the second most widely owned electrotherapeutic modality, although regularity of use was more limited. Similar levels of ownership were reported in 1993-4 in Northern Ireland, although use was again lower, except in the treatment of obstetric pain. A report on the use of TENS in Canada, where a quarter of all hospitals with 200 or more beds were surveyed, with an 84% response rate, indicated that TENS was available in all the hospitals. The devices were mainly located in the physiotherapy departments, and physiotherapists were the principal users. The most common applications were in the treatment of acute and chronic pain; however, there was a wide variation in the frequency of use.

It would therefore seem that TENS is widely available within physiotherapy departments, but there is a variation in use. This may be attributable to a lack of knowledge of the modality, and neurophysiological rationale underpinning it, or perhaps a lack of confidence with results.

Recent research findings and Implications for clinical use

There are many systematic reviews that have attempted to evaluate the clinical efficacy of TENS for acute and for chronic pain including knee osteoarthritis, rheumatoid arthritis, low back pain, neck pain, post-amputation pain, post-stroke pain, spinal cord injury, diabetic peripheral neuropathy, chronic and recurrent headache, neuropathic pain, and cancer pain. The largest meta-analysis of TENS to date provided the evidence that TENS alleviated chronic musculoskeletal pain. Often reviewers are unable to make definitive judgement about clinical efficacy because of inadequate Randomised Controlled Trial (RCT) design, poor reporting and concerns about trial fidelity and TENS technique.

A Cochrane review of 19 RCTs (1346 participants) found that TENS was superior to placebo TENS as stand-alone treatment for Acute Pain in adults. There were seven RCTs that investigated procedural pain in perioperative settings and four of these RCTs found that TENS was beneficial. Conditions included pelvic pain during office hysteroscopy (142 patients), pain during screening flexible sigmoidoscopy (90 patients), pain during unsedated colonoscopy (90 patients), pain during plastic surgery (100 patients). Three RCTS found that TENS did not confer benefit for procedural pain during laser treatment of the cervix (100 patients), intravenous needlestick techniques (71 blood donors), and flexible cystoscopy (148 patients). Simpson et al. conducted a meta-analysis of four RCTs and found that TENS reduced moderate-to-severe acute lower back pain, acute pelvic pain, renal colic, and pain associated with hip fracture by 28-44 mm (95% CI) on a 100 mm visual analogue scale. They recommended TENS for use by emergency medical services in prehospital settings.

In recent year,s a series of systematic reviews, some with meta-analysis, provide a growing body of evidence that TENS has clinical utility in post-surgical settings. Freynet et al. A reported that seven of nine RCTs found TENS reduced analgesic consumption and improved the duration of recovery room stay for patients with moderate pain associated with muscle sparing thoracotomy incision. Their review provided evidence that TENS was beneficial as a standalone treatment for mild post-thoracotomy pain (i.e. video-assisted thoracoscopy incision) but not for severe post-thoracotomy pain (i.e. posterolateral thoracotomy incision). In the same year, Sbruzzi et al. [13] provided evidence that TENS alleviated post-thoracotomy and sternotomy pain when combined with analgesic medication in a systematic review of 11 RCTs (570 patients). Subsequently, Kerai et al. found that TENS reduced the severity of pain and analgesic consumption for a variety of surgical procedures (eight RCTs, 442 patients) although they noted that studies lacked adequate sample size, robust methodology and consistency in TENS parameters. Beckwee et al. evaluated TENS for post-surgical knee arthroplasty pain (five RCTs, 347 patients) and reported that two studies found benefits during TENS. The three studies that did not find benefits delivered TENS at sub-optimal stimulation intensities. Gajjar et al. evaluated various analgesic treatments for colposcopy pain in women that included one RCT (100 women) which found that TENS did not provide additional benefit when combined with direct infiltration of lignocaine.

Conclusion

Evidence from systematic reviews of placebo controlled trials suggests that TENS alleviates pain and reduces analgesic consumption when administered using appropriate technique. Indirect benefits include improvements in pulmonary mechanics and general mobilization reducing the risk of chest infections, hypoxia, pressure sores and deep vein thrombosis. Thus, TENS should be considered as an adjunct to multi-modal management, including analgesic medication, for the management of acute post-surgical pain. Nevertheless, Randomized Controlled Trials (RCTs) on TENS often have small samples sizes which undermine confidence in the findings of systematic reviews. Meta-analyses of studies with small sample sizes have been shown to distort effect estimates of clinical efficacy. To improve confidence in estimates of clinical efficacy of TENS, there needs to be pooling of data from Randomized Controlled Trial(RCTs) with larger samples.

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