Transcutaneous Electrical Nerve Stimulation Unit
A transcutaneous electrical nerve stimulation (TENS) unit is used to apply electrical currents through the skin to the nerves via electrodes in order to reduce chronic and acute pain from various causes.
TENS is a noninvasive therapeutic pain management modality that is used alone or in conjunction with pain medications or other pain-management techniques. A TENS unit is used to transmit low-voltage electrical currents through the skin to the underlying nerves at the area where pain occurs. TENS is used to treat both chronic and acute pain associated with musculoskeletal problems (e.g., arthritis, low back pain), dental problems and procedures, bursitis, menstruation, urinary incontinence, surgical procedures, labor and delivery, fracture pain, and traumatic injuries. TENS is also used as an adjunct treatment for chemotherapy-induced nausea and vomiting.
A TENS unit consists of an electronic stimulus generator, which transmits electrical current to electrodes placed directly on the patient's skin. Most TENS units use two or four electrodes to transmit electrical impulses. The number of impulses (frequency), the pulse duration, and intensity can be adjusted. Some TENS units offer modulation, which allows the frequency, duration, and intensity to be intermittently changed, and a burst mode, which allows groups of rapid pulses to be applied at regular intervals. The treatment parameters (i.e., rate of stimulation, pulse intensity and duration, other settings) are based on the type of TENS unit used, the patient's medical condition, and response to stimulation.
The physiological mechanism of TENS pain relief is not fully understood, but two theories are have been proposed to explain it: gate control and endorphin release.
According to the gate-control theory, pain is experienced when certain small unmyelinated fibers are stimulated (the "gate" is opened). Pain is not felt when larger mylelinated fibers that inhibit the feeling of pain are stimulated (the gate is closed). The electrical currents produced by a TENS unit stimulate these large myelinated fibers, blocking pain stimuli transmitted by the smaller unmyelinated fibers.
According to the endorphin release theory, TENS is believed to stimulate the release of endorphins, peptides in the body that help inhibit the transmission of painful stimuli.
TENS units are available in desktop, handheld, portable, and wearable configurations, depending on the manufacturer and clinical applications for which the unit is designed. For example, some TENS units dedicated to
treating premenstrual pain and dysmenorrhea are smaller and configured with a belt clip and battery operation so the patient can wear the unit for the duration of pain treatment.
TENS is used in physical therapy, rehabilitation, primary care, hospital, chiropractic care, long-term care, and home-care settings, and is initially administered with close supervision of the patient to evaluate their response to treatment. Depending on their pain and associated medical condition, the patient may then given instructions on how to use the TENS unit at home according to a prescribed schedule.
To use a TENS unit, electrodes are placed on the patient's skin in the painful area, on either side of the spine, in peripheral nerve areas, or at trigger points, depending on the nature of the patient's pain. Electrodes should be kept at least 3 centimeters (1.18 inches) apart. The most common type of electrode supplied with the TENS unit is made of soft rubber that may require conducting gel before application. Other types of electrodes include those made of disposable foam or sponge that must be moistened with water, conductive self-adhesive polymer, or reusable pregelled material. Leads are then plugged into one end of each electrode and into output sockets on the electronic generator unit. Pulse rate, intensity, and duration are then adjusted according to the patient's condition; a vibration or tingling sensation may be felt and the muscles may twitch as the electrical pulses are delivered.
TENS should not be used in patients with tuberculosis, malignant tumors, high or low blood pressure, high fever, carotid sinus hypersensitivity, or acute inflammatory disease. Electrodes should not be applied over the eyes, the front of the throat, directly over a wound, on skin wet from bathing or sweating, over broken skin, or over psoriasis and similar skin conditions. Because TENS may interfere with pacemaker operation, electrodes should not be applied in the vicinity of a pacemaker, and TENS use in patients with pacemakers should be carefully supervised.
There are very few side effects associated with the use of a TENS unit. Minor skin irritation may occur from
the electrodes; proper cleaning of the patient's skin and changing the electrodes daily can alleviate irritation. Some sensitive patients may have an allergic reaction to gel or the electrode material. If TENS is applied in areas with poor sensation, skin burns may occur.
TENS units are, in general, low-maintenance systems that need only periodic battery checks to ensure effective delivery of the electrical pulses. Many TENS units have self-testing features that detect defective leads and electrodes; if the unit does not have self-testing features, leads and electrodes should be checked frequently to avoid potential shocks. Rubber electrodes can last years with proper cleaning and use; the leads should not be detached between uses, as this increases wear on the rubber and the connection. Pregelled reusable electrodes can be used for approximately one month or 100 hours.
Health care team roles
Depending on where the patient is being treated for pain and how TENS treatment is prescribed, a number of healthcare professionals could be involved. In physical therapy and rehabilitation settings, the therapist, nurse, or clinical assistant could administer TENS. In the hospital and primary care settings, physicians and/or nurses could administer TENS. Chiropractors, naturopathic physicians, and pain-management professionals (e.g., anesthesiologists) may also prescribe and administer TENS. The nurse or other clinician trained in the use of TENS can instruct patients using TENS at home, ensuring that they understand how to apply TENS and are compliant with their pain-management protocol.
Training in the use of the TENS unit is provided by the manufacturer for administration by clinical staff. Detailed manuals on maintenance and use are provided with the unit.
Electrode—A conductor used to complete the electrical circuit between the TENS unit and the patient.
Endorphins—A group of naturally occurring peptides that, when released, act like a painkiller by inhibiting the transmission of pain impulses.
Lead—Insulated wires that connect the TENS unit to the electrode.
Trigger points—Areas on the skin that, when stimulated electrically, produce sensations at that point or elsewhere on the body.
Walsh, Deirdre M., and Eric T. McAdams. TENS: Clinical Applications and Related Theory. New York: Churchill Livingstone, 1997.
Bertoti, Dolores B. "Electrical Stimulation: A Reflection on Current Clinical Practices." Assistive Technology 12, no. 1 (2000): 21–32.
American Academy of Pain Management. 13947 Mono Way #A, Sonora, CA 95370. (209) 533-9744. <http://www.aapainmanage.org>.
American Society of Anesthesiologists. 520 North Northwest Highway, Park Ridge, IL 60068-2573. <http://www.asahq.org>.
Society for Pain Practice Management. 4801 College Boulevard, Leawood, KS 66211. (913) 491-6451. <http://www.sppm.org>.
American Society of Anesthesiologists. "Practice Guidelines for Chronic Pain Management." Anesthesiology 86 (1997): 995-1004. <http://www.asahq.org/practice/chronic_pain/chronic_pain.html>.
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Jennifer E. Sisk, M.A.