In all of recorded birth history, women have grappled with the pain of labor and various pain relief methods. One method has remained in the background is the Transcutaneous Electrical Nerve Stimulation or T.E.N.S. Unit. Basically, the T.E.N.S. Unit provides a low level pulsed electrical current through electrodes place on the skin to give relief from pain.
As with most non-pharmacological pain relief methods, T.E.N.S. will not remove the cause of the pain and it does not have the same action as medications such as epidural anesthesia. It can, however, prevent the sensation of pain that felt during a contraction, by using comfortable electrical stimulation. The low level current activates nerve fibers in the skin, giving a different sensation. This sensation is transmitted to the brain and reduces the amount of pain felt. This is known as the Gate Control Theory. Pain fibers taking the pain stimulus to the brain are smaller and the sensation travels slower than the touch fibers, which are large. When touch and pain are stimulated simultaneously, the touch sensation travels to the brain and "closes the gate" in the brain, limiting the amount of pain perceived by the brain. The T.E.N.S. Unit stimulates these touch fibers.
There is also evidence that the T.E.N.S. machine enhances the production of the body's own natural pain killing substances: endorphins and encephalins. A woman's body produces endorphins and encephalins, which are opiate-like substances to counter the pain of the contractions in labor. The level of these substances rises as labor progresses - to match the rising intensity of contractions. These have several effects, including relaxation, a feeling of well being and help to bring relief from pain. Low frequency stimulation causes the release of the endorphins and encephalins.
Failure to release endorphins allows pain to occur. When pain medication is administered, natural endorphins are not produced. As the medication subsides, the natural endorphin level is not matching the pain sensation, which has been rising. This is the reason why when an epidural is turned off to allow the client a chance to push with her urge to push, the pain of the contractions is nearly overwhelming. It is important to note that it is theorized that endorphin production may be inherited and may be stimulated by a variety of alternative therapies such as massage and acupressure.
Some have also suggested that the T.E.N.S. Unit can be used to stimulate the secretion of oxytocin and prostaglandins (induction/augmentation), or used for electroacupressure during labor.
Putting the electrodes in the correct place is very important. If the electrodes are put in the wrong place your pain may not be lessened. The pain could even get worse if the electrodes are placed incorrectly. The electrodes should never be put near the eyes. The electrodes should also not be put over the nerves from the neck to the throat or brain.
Unlike medications, T.E.N.S. does not cause nausea, drowsiness, or limited activity. T.E.N.S. may sometimes cause skin irritation or redness. Usually this disappears quickly or can be prevented by using alternative gels or electrodes.
There are no known contraindications for using the TENS. Unit, however the Unit should never be used on a person with a pacemaker or defibrillator.
Even though there are few side effects and minimal contraindications, there are several precautions to be aware of when using a T.E.N.S. Unit. The safety of T.E.N.S. during pregnancy (prior to 36 weeks) has not been established, so it should be used with the knowledge of the physician or midwife. T.E.N.S.stimulation is of no curative value. That is, T.E.N.S. does not do anything to the underlying cause of the pain (contractions). Electrical stimulation over the carotid sinus, i.e. anywhere over the front of the neck, may be hazardous.
Medical experts generally agree that a T.E.N.S. Unit should not be used in the following situations:
- Placement should never be over the anterior part of the neck.
- People with cardiac problems.
- People with carotid sinus. TENS may cause slow heart beat or bradycardia.
- Directly over any wound. Over the uterus of a pregnant woman.
- Over the eye.
- People with pacemakers or personal defibrillators.
For more information:
Dunn, P et al. Transcutaneous electrical stimulation at acupuncture points in the induction of uterine contractions. Obstetrics and Gynecology. 73: 286-290. 1989.
Eappen, and Robbins, D. Nonpharmacological Means of Pain Relief for Labor and Delivery. International Anesthesiology Clinics. 40(4):103-114, Fall 2002.
Hundley, V., et al. Midwife managed delivery unit: a randomised controlled comparison with consultant led care. BMJ 1994;309:1400-1404 (26 November)
Tenore JL. Methods for cervical ripening and induction of labor. American Family Physician. 2003 May 15;67(10):2123-8.
Tsuei, J. and Leuizi. Y. The influence of acupuncture stimulation during pregnancy. Obstetrics and Gynecology. 50: 479-488. 1977.