Electrotherapy is the use of electrical stimulation for therapeutic purposes. Specifically, electrotherapy uses energy waves that are part of the electromagnetic spectrum to produce desired physiological and chemical effects in the body.
Purpose
Electrotherapy is used for three therapeutic purposes: (1) to relieve pain; (2) to stimulate physiochemical changes; and (3) to stimulate muscle contraction.
Pain relief
For pain management, the two commonly used modalities of electrotherapy are transcutaneous electrical nerve stimulation (TENS) and iontophoresis. TENS relieves pain by stimulating proprioception nerve fibers to block the transmission of competing pain signals. Although both proprioception and pain receptors respond to electrical stimulation, there is some evidence that the proprioreceptive nerves respond to different kinds of waveforms from the forms that stimulate pain receptors; TENS uses the electrical waveforms that target proprioreceptors.
Electrodes are generally placed at points of pain, trigger points, acupuncture points, or over nerve roots. Parameters determining the character of the TENS stimuli are selected; these parameters include the waveform, frequency, duration, and amplitude of the wave. The duration of each TENS session is usually one hour. A typical patient is prescribed TENS four times daily for initial pain control. With continued use and as pain decreases, the frequency of TENS sessions can gradually be reduced to two sessions or one session daily.
The use of TENS for pain management is covered by insurance, but only for specific types of pain for limited time periods. TENS is typically well-covered for acute postoperative pain management, but TENS use for chronic pain complaints varies by insurer. Although the use of TENS to relieve labor and delivery pain has been documented overseas, this application of TENS is generally not approved by insurers in the United States.
A second form of electrotherapy used for pain relief is iontophoresis. Iontophoresis refers to the transdermal (through the skin) introduction of ionic compounds using direct current. This method of pain management is sometimes covered by insurance. In the United States, iontophoresis is almost always administered using dedicated iontophoresis devices. These machines allow for the fine-tuning of treatment parameters such as the amplitude of the current, the duration of treatment, and the automated ramping up and down of current at the start and end, respectively, of each treatment session. Iontophoresis units also come equipped with electrodes embedded in fiber pads or gel that carry the desired drug. For pain management, the drugs used in iontophoresis are analgesics and anti-inflammatory compounds, and include such medications as dexomethasone, lidocaine, and salicylate.
To begin iontophoresis, the delivery electrode containing the drug is placed in the area where pain is reported. Whether a drug is placed at the site of a negative or a positive electrode depends on the drug's ionic charge. Lidocaine has a positive charge and is placed with a positive delivery electrode, while the negatively-charged compounds of dexomethasone and salicylate are used with a negative delivery electrode.
After securing the delivery electrode, a second electrode, of opposite polarity, is placed on the body at a fixed distance (determined by the particular iontophoresis unit) away from the first electrode. Lead wires are attached to the electrodes, with the positive lead attached to the positive electrode and the negative lead to the negative electrode. The intensity of the electric current is then slowly increased until the predetermined level is reached, and this level is maintained throughout the main treatment session.
Treatment "dosages" are given in terms of milliampere-minutes—that is, the product of the amplitude of the current (in milliamperes, mA) and the duration of treatment (in minutes). For example, a treatment consisting of two mA for 30 minutes would be a dose of 60 mA-min. Note that such a recommended dose would also allow the therapist to administer a treatment session of three mA for 20 minutes. In general, dosages range from 40 to 80 mA-min, with current intensity ranging from one to four mA, and treatment duration ranging from 20 to 40 minutes.
Stimulation of physiochemical changes
Diathermy and radiation are two forms of electrotherapy that are used to induce physiological and chemical changes in the body. Diathermy refers to the use of high-frequency electromagnetic waves (greater than 10 MHz) as therapeutic stimuli. Shortwave diathermy uses waves of 13, 27, or 45 MHz, while microthermy uses waves of up to 2450 MHz in frequency. Both forms of diathermy generate heat in deep muscle tissue, although microthermy is believed to be absorbed more by superficial fatty issue.
The patient is placed between the electrodes, and the power level is adjusted until the patient reaches resonance (as determined by automated measurement systems) with a pre-established heating level. Each diathermy session lasts 10–30 minutes, depending on the size of the target area. The heat generated by diathermy is believed to improve blood circulation, relax muscular tension, and promote drainage in the target areas. Because of the lack of large controlled studies of diathermy, it may not be covered by insurance.
Radiation therapies in the context of electrotherapy include infrared, ultraviolet, and coldlaser therapies. Infrared therapies—heat lamps, moist heat packs, and chemical heat packs—are used to apply superficial heat to improve circulation in target areas. Ultraviolet lamps are thought to stimulate the body's production of corticosteroids and vitamin D. For some therapies, ultraviolet radiation is used in conjunction with photosensitive or photoactivated medications. Cold laser treatments—most commonly, the directing of a low-powered helium-neon laser beam over the target area—are used to facilitate wound healing. Cold laser may also be used for pain relief, with the laser directed at acupuncture points, trigger points, and nerve roots. Typically, ultraviolet and cold laser treatments do not exceed two minutes, while infrared treatments can last between 10 and 30 minutes.
Infrared or heat therapies are viewed as conventional treatments and are covered by insurers as part of a short-term physical therapy regimen. Ultraviolet therapies, however, are only covered for very specific dermatological conditions such as disabling psoriasis. Cold laser treatments are categorized as investigational, or experimental, therapy and are not covered. Large uncontrolled trials have shown some benefits of cold lasers in promoting wound healing, but smaller controlled trials have shown little or no benefit. Studies of the pain-relieving effects of cold laser suggest no benefit beyond that which can be obtained through conventional treatments.
Stimulation of muscle contraction
The use of electrical stimulation to stimulate muscle contraction is known as neuromuscular electrical stimulation (NMES) or functional electrical stimulation (FES). NMES/FES therapies apply pulses of electrical current to target muscle groups to stimulate active motion, strengthen muscles, and prevent muscle atrophy.
In NMES/FES, electrodes are placed initially on the belly of the muscle that is to be stimulated. AC electrical stimulation is then applied at low levels (threshold levels for muscle movement). Based on muscle responses to the threshold stimulation, electrode positions are adjusted until the motor points of the muscle (optimal positions for generating muscle movement) are found. Electrodes are then secured at these optimal positions.
After the electrodes have been placed, parameters for NMES/FES are programmed into the electrical stimulator unit. Parameters include the amplitude of the electrical pulse, the duration of each pulse, the frequency of pulses, the duration of on/off (activation/rest) periods during the treatment session, ramping modulation (gradual increases and decreases) in stimulation, and duration of the treatment session. The maximum pulse amplitude recommended for NMES/FES is generally the maximum amplitude that can be tolerated by a given patient. Regarding pulse duration, there remains some ambiguity about the optimal duration time of each pulse; current practices suggest that pulse duration be set between 50 and 1000 microseconds. Pulse frequency tends to range from 30 pulses per second to 100 pulses per second. Since continuous electrical stimulation leads to early muscle fatigue, treatment sessions include rest periods between activation periods. The duration of "on" (activation) periods is typically 10–15 seconds; "off" (rest) periods can last up to one or two minutes. Treatment sessions may last between 10 and 20 minutes, and usually do not exceed one hour.
Electrical stimulation can begin after parameters are set. In general, the intensity of the stimulation is increased from contraction to contraction within a given session, and is also increased from session to session, depending on how well the patient tolerates the increases.
NMES/FES is usually approved by insurers for post-surgical rehabilitation and rehabilitation after immobilization (after a limb has been in a cast or splint). This form of electrotherapy is typically not approved for spinal cord injuries or for muscles that have been denervated.
Precautions
Although each modality of electrotherapy has its specific set of contraindications, cardiac pacemakers are a general contraindication for electrotherapy. Electrical signals from electrotherapy devices can interact with the electrical signals from pacemakers and interfere with pacemaker functioning. Pacemaker disruption is particularly acute with such modalities as diathermy and electrical nerve stimulation. However, less interference may occur with such radiation modalities as infrared, ultraviolet, and cold laser treatments (these modalities are discussed in detail below in the Description section).
Contraindications for pain relief electrotherapy include:
undiagnosed pain (pain is a symptom that might signal a serious condition that may need to be treated directly)
current use of narcotic medications that can desensitize patients to stimuli
Preparation for electrotherapy requires first that the physical therapist clarify the problem area and condition with the patient. The physical therapist then selects the appropriate therapeutic modality for the complaint and determines the relevant parameters for each electrotherapeutic modality.
The skin of the target area must be clean. For modalities requiring electrodes, the skin of the target area must also be free of lesions. For TENS therapy, conduction gels are used on the surface of the skin; otherwise, moisture on the tips of the electrodes is sufficient. For ultraviolet therapies, a small area of the skin should be tested to determine the minimal erythema (reddening of the skin) dosage prior to treatment. For some ultraviolet therapies, a photosensitizing medication is given prior to treatment.
If pain relief is the goal, the patient should discontinue the use of pain medications that might obscure the effect of electrotherapy. For iontophoresis, the patient must be queried on possible sensitivities; for example, an allergy to dexamethasone would rule out the use of dexamethasone as an anti-inflammatory ionic substance.
Aftercare
Patient comfort should be monitored throughout the therapeutic session. After treatment, the patient should be queried about excessive levels of discomfort. Excessive discomfort should serve as a guide for modulating electrotherapy parameter settings in the future.
In the case of such direct electrical stimulation as NMES/FES, the skin under the probes should be massaged with a neutral cream after treatment.
Complications
After treatment, the patient should be checked for burns from electrodes or poorly placed wires. Heat burns are possible with almost all electrotherapy modalities. These types of burns occur when there is a buildup of heat in regions where electrical resistance is high. Causes of these high-resistance burns include electrodes being placed in sclerotic (scarred) areas; electrodes being placed in areas with wrinkled or folded skin or other areas where electrode contact is poor; or electrodes being poorly moistened.
A complication of iontophoresis is chemical burn. Chemical burns occur when too much sodium hydroxide accumulates at the negative electrode. A pink lesion is apparent immediately after treatment, which becomes an oozing wound two to three hours later. This type of burn can be treated with antibiotics and a dressing, but tends to heal slowly. This complication can be prevented by decreasing the intensity of the current or by increasing the area of the negative electrode so that the current is dispersed over a larger area.
Complications arising from cold laser treatment include dehydration, protein coagulation (clumping), and thermolysis (melting). While dehydration is reversible, protein coagulation and thermolysis are not. The typical cause of these complications is the use of cold laser at excessively high power.
Results
TENS and iontophoresis should result is a reduction of pain and/or reduced symptoms of inflammation. There may be a concomitant increase in range of motion.
If diathermy and radiation are used, improved drainage may be reported. In addition, depending on the specific therapy, improvement in skin conditions and wound healing are expected. The reduction of pain and inflammation may also be reported.
NMES/FES should maintain or improve muscle strength. If the electrical stimulation is used to alleviate muscle spasm, relief from spasm is an expected result.
Health care team roles
Because the physical therapist has typically received training in electrotherapy during his/her course of studies, he/she is the primary care provider during electrotherapy. The physical therapist delivers the therapeutic care and monitors the patient during electrotherapy. If the patient has been referred by a physician or other health care provider and the provider requests briefings, the therapist reports on the effects of the therapy and on the patient's progress.
KEY TERMS
Denervation—A lack of nerve input into a muscle, organ, or other body part that normally receives neural input.
Innervation—The presence of nerve input into a muscle, organ, or other body part.
Osteogenesis—New bone growth.
BOOKS
Kahn, Joseph. Principles and Practice of Electrotherapy. 4th ed. New York: Churchill Livingstone, 2000.
Low, John, and Ann Reed. Electrotherapy Explained. Boston: Butterworth Heinemann, 2000.
Nelson, Roger M., Karen W. Hayes, and Dean P. Currier, eds. Clinical Electrotherapy. 3rd ed. Stamford, CT: Appleton & Lange, 1999.
