Transcutaneous electrical nerve stimulation (TENS) works by a phenomenon called “gate control theory.” There are multiple receptors in the periphery and the spinal cord fibers that transmit peripheral information but cannot transmit information from multiple receptors simultaneously, so the stimulation of multiple receptors at the same time results in decreased signal from each to the brain. TENS units, by providing a low-dose electrical current, stimulate vibration receptors, which — when applied to an area having pain — reduces the transmission of painful stimuli to the brain.

Acute or chronic pain in any area of the body not listed as a contraindication

Do not place TENS units or electrodes:

• Over the eyes
• On opposite sides of the head, which would result in a transcerebral current.
• On the chest and back, which would result in a transthoracic current.
• On the anterior neck because of the possibility of a vasovagal event or laryngospasm.
• Internally.
• Directly over the spinal column.
• Near any sort of implantable device (spinal stimulator, pacemaker) where current from the TENS would interfere with the device.
• Over the uterus in a pregnant woman.

For pacemakers or pacemaker/defibrillators, a TENS unit must be placed at least 6 inches from the pacemaker. During initial TENS unit placement, the patient should be on a cardiac monitor to watch for any interference.

A TENS unit consists of the following:

• Pulse generator or electrical stimulus generator: a small electrical device about the size of a smartphone that controls the current delivered to the patient
• Connection wires: connect the pulse generator to the electrodes, usually with a single wire that plugs in to the pulse generator and splits into two connections, one for each electrode
• Electrodes: small sticky patches, similar to ECG electrodes, that attach to the skin and are the site at which the electrical current is delivered to the patient.

Identify the area of the patient’s greatest pain.

Electrode placement - single channel TENS therapy:

• Place two electrodes on either side of the area of greatest pain. The orientation of the electrodes can be left/right or above/below the area of pain.
• Connect these electrodes to the wire and plug into the pulse generator.

Electrode placement - dual channel TENS therapy:

• Place two electrodes on either side of the area of greatest pain, in a left/right orientation. Connect these electrodes to a wire and plug into the pulse generator.
• Place two more electrodes on either side of the area of greatest pain, in an above/below orientation. The area of greatest pain is now surrounded on four sides, like a framed picture, by electrodes. Connect these electrodes to a wire and plug into the pulse generator.

Alternative electrode placement – dual channel TENS therapy

• If the patient has pain in more than one area, the provider can place one set of electrodes on either side of one area of pain, and a second set of electrodes on either side of a second area of pain, allowing for treatment of two areas at once

Operating the TENS unit

• Most devices have preset settings for different parts of the body. These vary in the amplitude, pulse duration, and pulse frequency of the electrical current to provide the most relief of pain.
• Multiple different devices exist on the market, so providers should be familiar with the unit they will be using to treat patients.
• Once the electrodes are applied, use either the unit’s basic setting or a body-part specific setting (if available).
• Slowly increase the intensity of the treatment (usually controlled with an Up/Down button like the volume on a TV remote control) until the patient feels relief of pain and a pleasant buzzing sensation where the electrodes have been placed.
• Allow the patient, with provider assistance if needed, to adjust the settings of the device to maximize pain relief. This may take some experimentation by patients and providers to find the setting that is most effective.

Some manufacturers also make smaller “fixed site” or “wireless” units which can be focally applied to areas of pain, allowing for patients to be more active while using TENS.

• Patients, when using units at home, can use the unit multiple times per day but should not use the unit continuously, due to the risk of skin breakdown under the electrodes.

Document where the unit was applied.

Consider documenting for future reference the settings used.

Multiple manufacturers produce TENS units. Most manufacturers have information for patients and providers about using TENS, as well as specific information about their brand/model of TENS.

Physical therapy has been using TENS regularly and can provide insight on ways to optimize use of TENS. Ask one of your hospital’s physical therapists for advice or to show you how they use one in their practice.