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Understanding the effective use of a TENS machine

Pain | December 20, 2014 | Author: The Super Pharmacist

Pain

Understanding the effective use of a TENS machine

A transcutaneous electrical nerve stimulation (TENS) machine uses an electric current to stimulate nerves for therapeutic purposes. A TENS machine is a small, electrical (often battery operated) device that has leads connecting to electrodes that are then attached to the skin using adhesive pads. Small electrical impulses are then delivered to the part of the body where the pads have been placed, where they carry out two main functions:

  • The blocking/interruption or reduction of pain signals travelling to the spinal cord and brain to reduce or alleviate muscle spasms
     
  • The stimulation of the production of endorphins (the body’s natural analgesic)

The use of an electrical charge for pain relief is well documented throughout history, with the first documented incidence recorded by the physician to the Roman Emperor Claudius in AD46 after he stood on an electric fish to relieve his pain (1). The first modern, officially patented TENS machine was registered for use in the US in 1974.

How effective is a TENS machine?

TENS machines commonly play a role in the reduction of muscle spasms and pain in a wide range of conditions and circumstances, including:

  • Knee pain
  • Arthritis
  • Sports related injuries and accidents
  • Period pain
  • Back pain
  • Neck pain
  • Labour

TENS is a popular treatment option for many healthcare professionals and patients alike: it is non-invasive, non-pharmacological, relatively cheap, portable and patient controlled (2).

Yet the effectiveness of TENS machines, and the evidence that underpins their use, is often conflicting. A wide range of systematic reviews have considered TENS studies in a number of situations including post-operative pain, childbirth, and the areas listed above.

Of 17 randomised controlled trials (RCTs) that were recently covered, all but 2 of them found TENS to have no analgesic property or benefit in the post-operative period (3).

In an additional systematic review in the same year, an additional 20 studies of postoperative pain were reviewed, with only 12 evidencing positive TENS-related outcomes (4).

A systematic review undertaken in 2009, covering another 12 RCTs, evidenced that only one out of five studies comparing TENS with a placebo treatment found TENS to have a statistically significant effect (5). There is relatively limited data and evidence concerned with the use of TENS machines in conjunction with other analgesics, although the majority of studies that are solely concerned with TENS as a treatment option are unequivocal in stating that TENS is not effective as the sole treatment of both moderate and severe pain.

There is further evidence to suggest that TENS machines may have a positive role to play in the treatment of leg ulcers, with the hypothesis being that it induces vasodilation and the release of endorphins (7,8). There is no evidence for its role in reducing pain in patients with osteoarthritis, with a review of 18 eligible trials for knee related pain concluding that there was a lack of adequate evidence in regards to its effectiveness (9). There are no specific studies regarding the role of TENS machines in improving the circulation of blood around the body, despite this being a commercial selling point for many machines in the marketplace.

TENS are also frequently synonymous with labour and childbirth, despite there being very little formal evidence for their use and no record of effectiveness in either labour or postoperative pain (6). However, its ongoing popularity may also be in part due to its non-invasive nature, and its use in place of other analgesic interventions that might pose a greater threat to the wellbeing of both Mother and child.

This is one of many practical example where further information, and larger trials, would benefit the TENS machine evidence base.

What are the safety considerations regarding TENS?

There are a number of safety concerns associated with TENS machines that can usually be countered with sensible use and appropriate consultation with a qualified healthcare professional. There are several anatomical and physical locations where TENS cannot be used, including:

  • On the front of the neck due to the risk of acute hypotension
  • Broken skin areas, and open wounds
  • Over tumours or malignancy (electrical stimulation can promote cell growth)
  • Over a pregnant uterus (the impact of electrical stimulation on the developing foetus is not known)
  • Through the chest, using an anterior and posterior electrode position (10)

A literature review also suggests that TENS machines should be avoided in patients with cardiac pacemakers (11). It is also advised that TENS be used with caution on areas of skin that are numb or have decreased sensation, over areas of infection, and in people with epilepsy.

Limitations of TENS evidence

Limitations of TENS evidenceAs well as being a relatively limited body of literature on which to base recommendations regarding TENS machines, there are also methodological issues with each study that ensures all advice must be approached with a degree of caution. A recent paper that investigated the study designs that have been used for TENS related randomised controlled trials highlighted a range of common factors in under-researched topic areas or medical devices:

  • small sample sizes
  • poor or inadequate randomisation and blinding
  • poorly defined outcome measures
  • the incorrect placement of TENS electrodes
  • inadequate intensity and treatment duration (12)

In regards to comparative studies between TENS machines and placebos, it is very difficult to blind patients to the fact they will not be receiving electrical paresthesia (a sensation of tickling, tingling, pricking or burning with no long lasting effect). These methodological limitations in TENS related study designs go some way towards explaining some of the conflicting advice that exists in regards to its ability to provide effective pain management for a range of conditions. An absence of evidence is not necessarily indicative that TENS machines are not effective, and there is some empirical evidence to suggest that some patients do find them effective in the treatment of pain.

Despite the lack of evidence regarding their efficacy, it is likely that TENS machines will continue to be used in pain management clinics due to its lack of side effects, cost and non-invasiveness when compared to other analgesics that come with the risk of additional medical complications (13). 

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References

1. Walsh D (1997). TENS: Clinical Applications and Related Theory. London: Churchill Livingstone.

2. Wright A (2012). Exploring the evidence for using TENS to relieve pain. Nursing Times 108:11, 20-23.

3. Carroll D (1996). Randomization is important in studies with pain outcomes: systematic review of transcutaneous electrical nerve stimulation in acute post-operative pain. British Journal of Anaesthesia 77:798-803

4. Reeve et al (1996). Transcutaneous electrical nerve stimulation (TENS): a technology assessment. Intl Journal of Technology Assessment in Healthcare 12(2) pp.299-324

5. Walsh D (2009). Transcutaneous electrical nerve stimulation for acute pain. Cochrane Database of Systematic Reviews Issue 2, Art No. CD001642

6. McQuay H, Moore R. (1998). Transcutaneous electrical nerve stimulation (TENS) in chronic pain. In: An Evidence-based Resource for Pain Relief. Oxford: Oxford University Press.

7. Asbjornsen G. (1990). The effect of transcutaneous nerve stimulation on pressure sores in geriatric patients. Journal of Clinical and Experimental Gerontology. 12(4) pp.209-214

8. Kaada B. (1983). Promoted healing of chronic ulceration by transcutaneous nerve stimulation (TNS). VASA. 12: pp.262-269

9. Rutjes A. (2009). Transcutaneous electrostimulation for osteoarthritis of the knee. Cochrane Database of Systematic Reviews, Issue 4.

10. Watson, T. (2008). Electrotherapy: Evidence-Based Practice. London: Churchill Livingstone

11. Digby, G. et al. (2009). Physiotherapy and cardiac rhythm devices: a review of the current scope of practice. Europace 11: pp.850-869

Bennett, MI. et al. (2011). Methodological quality in randomised controlled trials of transcutaneous electric nerve stimulation for pain: low fidelity may explain negative findings. Pain 152:6,pp.1226-1232

Binder A, Baron R. (2010). Utility of transcutaneous electrical nerve stimulation in neurologic pain disorders. Neurology. 74:2 pp.104-105.

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