Keep electric therapy effective and safe for all patients
“Positive” versus “Negative” Electrode Placement. Every therapist should realize that with alternating current (AC) each electrode reverses current with each cycle. In other words, the red and black change from positive to negative. On the other hand, galvanic or direct current (DC) has a true positive and a negative. It is extremely important where you place the red (anode) and black (cathode) electrodes. When using direct current one electrode will be an “active” treatment electrode and the second “non-active” treatment electrode is just used to complete the cycle.
Muscle Contraction. Therapists can mistakenly believe that in order to have physiological benefits from electrical stimulation a muscle contraction must be seen or palpated. Although a contraction is warranted when using electrical stimulation for maximum fiber recruitment and muscle pumping for edema reduction (see fig. 1), it is not always warranted in pain management and never warranted in electrical stimulation for tissue repair.
Frequency. Unlike ultrasound, where frequency is changed to affect depth of penetration (inversely proportional), you change the electrical frequency to stimulate different nerve fibers. The general rule is as follows: high frequency (50 Hz-200 Hz) for acute pain to stimulate sensory fibers, and low frequency (1 Hz-15 Hz) for chronic pain to stimulate motor fibers. In order to increase the electrical current depth of penetration, instead of increasing voltage, it is much more comfortable for the patient to use an interferential current technique.
Resistance. Often, patient resistance to electrical conduction is simply overlooked. Examples include skin dehydration, scar tissue, worn out adhesive on surface electrodes, and improper skin preparation such as failure to remove barrier creams all increase resistance. In contrast, abrasions/cuts and acupuncture points (often correlating with trigger points) have decreased electrical resistance and can be hypersensitive. Remember that changing frequency does not affect resistance. Frequency is not part of Ohm’s law.
Intensity. The intensity or amperage should not be constant but should be changed according to desired effect with each patient and treatment. For example, every day a patient may require a small change in intensity in milliamps (ma) to achieve a desired muscle twitch or contraction. Also, different types of current have different wave forms and will require varying changes of intensity. If the intensity is increased to the point that the patient is not tolerating treatment you can decrease the intensity required by increasing the pulse width.
Presence of Infection. Many therapists will stop treating wounds with electrical stimulation upon signs and symptoms of infection. Research shows that electrical stimulation such as high-volt pulsed current, also known as pulsed direct current, has bactericidal effects. The one exception: Never treat a patient with osteomyelitis, because you can stimulate healing and closure over the infected area and cause an abscess.
Presence of Metal. Unlike short wave diathermy, it is not contraindicated to use electrical stimulation over metal (i.e., compression screws, metal plates, wires, joint replacements). Electrical stimulation brought to a tingling sensation for pain reduction is appropriate following an open reduction external fixation.
Presence of Fracture. It is not contraindicated to use electrical stimulation for pain management of fractures; a positive side effect is that electricity has long been known to be a stimulus for osteogenesis. Transcutaneous electrical nerve stimulation (TENS) or medium frequency alternating current (MFAC) in a quad-polar setup can be used (see fig. 2). Intensity should be increased to a pleasant tingling sensation; do not elicit a muscle contraction.
Mechanism of Action. TENS and MFAC nerve block can block pain transmission, but by different physiological methods: TENS via gate control therapy or the release of met-enkaphalin and dynorphin on the “c” fiber (synaptic inhibition), and continuous MFAC nerve block via nerve membrane depolarization (Wedensky inhibition). Interferential current is two MFAC whose amplitude is summated to form a vector current field to increase current into deeper tissue. It can be used for pain relief by releasing endorphins.
Contraindications. Do not assume that just because a physician has ordered electrical stimulation or TENS that they have been thoroughly checked for contraindications such as an implanted medical device (cardiac pacemaker, defibrillator, insulin or balcofen pumps), active cancer or sepsis. Have backup plans should contraindications arise. For example, instead of using electrical stimulation, contrast baths can be used for edema reduction, or use subthermal ultrasound for pain relief on an intercostal muscle tear rather than run electrical current transthoracically.