Transcutaneous electrical nerve stimulation (TENS) devices

What are Transcutaneous Electrical Nerve Stimulation (TENS) devices?
What is it used for?
How does it work?
Using TENS devices
Benefits
Limitations
Risks

What are Transcutaneous Electrical Nerve Stimulation (TENS) devices?

TENS or transcutaneous electrical nerve stimulation devices are used in the treatment of pain. A TENS device works by passing a small electrical current across the skin. This procedure is completely painless.

TENS machines or devices became popular in the 1970’s and are commonly used by physiotherapists today. Many people will report a reduction in pain after TENS treatment or therapy. However, research evidence to support these patient reports is mixed.

What is it used for?

TENS devices are primarily used to treat various forms of pain including chronic musculoskeletal pain (for example arthritis or back pain), pain that occurs following an operation or surgery, cancer pain, phantom limb pain (pain in an already amputated arm or leg, as if it were still there) and pain during childbirth.

TENS has also been reported to be useful in reducing nausea following chemotherapy and in the healing of ulcers or wounds.

How does it work?

A TENS device will typically consist of an electrical pulse generator, leads and electrodes. When switched on, the electrical pulse generator will create waves or pulses of electricity that travel along the leads to the electrode that are placed on the skin. The electrodes are placed either near to the site of the pain, or sometimes along the spinal cord. The patient or practitioner can control the electrical pulses and alter their amplitude (whether the pulses are strong or weak), frequency (how often the pulses occur) and duration (how long the pulses last for).

TENS devices can be portable, battery powered and easily operated by patients. These TENS devices tend to be small and lightweight, and can be concealed under clothing. Other TENS devices may be powered through an electrical outlet and will tend to be larger. These devices will typically require a physiotherapist or technician to operate them.

There are two theories about how electrical pulses generated by TENS devices may relieve pain. One theory suggests that the electrical pulses may aid in the release of endorphins – the body’s natural pain-killers. Another theory (the gate control theory) suggests that electricity can stimulate nerve fibres that will block pain messages to the brain.

Using TENS devices

TENS devices are usually available at physiotherapy centres and at some hospitals. Small TENS devices are also available for commercial sale to patients.

There are no strict guidelines on how long a TENS device should be used for. An initial session will generally last for 10 to 30 minutes. The intensity of the electrical pulse will be set below a patient’s pain threshold. However the patient should feel tingling, prickling or buzzing sensations called paraesthesias.

Pain relief usually occurs soon after the onset of the electrical pulses, and should persist for at least the time that the machine is switched on. Patients may use the TENS device at home as needed. Alternatively, TENS can be applied at fixed intervals, two or three times daily. Patients are often encouraged to experiment with pulse amplitude, frequency and duration to maximise their comfort.

TENS devices should not be used while driving or operating machinery, should never be used near water (e.g. in the shower) and should not be used near an open wound, or on broken or irritated skin.

Benefits

TENS devices are thought to reduce the severity of pain. TENS devices can be relatively easy to use and accessible for patients. When used appropriately, there are no known side effects of these devices.

Limitations

Currently, there is mixed support for the use of TENS devices in the treatment of pain. Some studies have found pain reduction following the use of TENS whereas others have found no significant reduction in pain.

Risks

If the TENS device is not used appropriately (i.e. at high voltages) there is a risk of increasing pain rather than easing it.
TENS is not recommended for use on pregnant women as it may induce contractions.
TENS is not recommended for individuals with cardiac pacemakers. The electrical pulses may interfere with the operation of the pacemaker.
TENS is not recommended for patients with epilepsy or severe allodynia (e.g. a heightened pain response to gentle touch).
It is recommended that TENS electrodes should not be placed over the throat, eyes or carotid sinus (the area on the neck just below the ear and near the jaw where the carotid artery lies).

References

Bercovitch M, Waller A. Transcutaneous electrical nerve stimulation (TENS). In: Doyle D, Hanks G, Cherny N, Calman K, editors. Oxford Textbook of Palliative Medicine. 3rd ed. Oxford: Oxford University Press; 2004. p. 405-410.
Johnson M, Martinson M. Efficacy of electrical nerve stimulation for chronic musculoskeletal pain: A meta-analysis of randomized controlled trials. Pain 2007; 130: 157-65.
Bjordal J, Johnson M, Ljunggreen A. Transcutaneous electrical nerve stimulation (TENS) can reduce postoperative analgesic consumption. A meta-analysis with assessment of optimal treatment parameters for postoperative pain. Eur J Pain 2003; 7: 181-8.
Carroll D, Tramer M, McQuay H, Nye B, Moore A. Randomization is important in studies with pain outcomes: systematic review of transcutaneous electrical nerve stimulation in acute postoperative pain. Br J Anaesth 1996; 77(6): 798-803.
Melzack R, Wall P. Pain mechanisms: a new theory. Science 1965; 150: 971-9.