Transcutaneous electrical nerve stimulation (TENS) is in essence application of electric current for control of pain. It involves a principle wherein the sensory myelinated fibers are stimulated without discomfort to the patient and without muscle contraction. TENS is a non-invasive, very safe method to reduce pain, both acute and chronic. While there are conflicting views on its efficacy, its effectiveness for postoperative pain, osteoarthritis, and chronic musculoskeletal pain has been confirmed by systemic reviews.
How Does TENS Act?
The stimulation activates local inhibitory circuits within the dorsal horn of spinal cord. These inhibitory circuits reduce the transmission of painful impulse through the spinal cord.
This stimulation is done by a frequency of 70 Hz, patients feel comfortable at this level of stimulation. TENS equipment has a frequency of 1 to 100 Hz. When stimulated at a high frequency of 70 Hz, the pain relief is shorter and of fast onset.
But stimulation at low frequency has a slow onset of pain relief and long after effect. Some types of equipment have a combination of both, high-frequency bursts repeated at low frequency. Clinically rectangular waveform width between 0.1 to 0.5 msec is utilized. The current is delivered through electrodes with gel application.
- Patients with pacemakers
TENS is used for chronic pain and in stimulation of bone fracture healing.
- For chronic pain, 3 hrs sitting per day for 4 to 6 weeks.
- Allergic response to gel/electrode with local erythema.
- Painful stimulation with inadequate gel application.
TENS does a good job initially, providing good relief upto 70 percent to start with. As time passes, the pain relief remains at about 20 percent to 30 percent. But its noninvasive nature, portability and domestic use are quite attractive.
TENS is ineffective in psychogenic pain and pain of multiple sites.
TENS electrodes should not be placed
- On or near the eyes
- In the mouth
- Transcerebrally i.e. On either side of temple
- On the front of the neck due to the risk of vasovagal reflex leading to hypotension
- On areas of numb skin/decreased sensation
- On broken skin areas or wounds
- On or near the trigeminal nerve if you have a history of herpes zoster induced trigeminal neuralgia.