There are two types of electrical current: direct and alternating. Direct current (DC), often delivered as pulsed current (PC), is utilized for wound healing since it produces polarity changes in target tissues. Alternating current (AC) generates a balanced, sinusoidal waveform that produces an overall neutral charge in target tissues. (FIGURE 14-8 illustrates the types of electrical current.) Since polarity is an important factor in utilizing ES for tissue healing, AC units are not recommended for use in wound management.7
ES Precautions and Contraindications
||Download (.pdf) Table 14-6
ES Precautions and Contraindications
|Precautions || |
Children <3 years of age5
Skin irritation or burns under electrodes
Use in areas of impaired or absent sensation
Skin irritation/burns from ion shifts
|Contraindications || |
Malignancy in wound or periwound tissue18,38
Overimplanted electrical devices or any patient with a pacemaker18,20
Over the heart18
In wounds with metallic ion residue (eg, povidone-iodine, silver, or zinc)18,38
In close proximity to a developing fetus20
Over areas of active bleeding
Position such that current would flow through the anterior neck or upper chest5
When DC is applied to tissue, the anode (positively charged electrode) will attract negatively charged cells and the cathode (negatively charged electrode) will attract positively charged cells. With PC, the flow of direct current is interrupted or pulsed at brief intervals with a finite “off” time between each pulse.7 Short pulse duration combined with biphasic current (shifts in polarity) can make PC delivery more comfortable than DC and prevent potentially harmful ion changes under the electrodes.5 These two properties of PC make it the primary method of ES delivery for wound healing. The two most common types of ES for wound management utilize pulsed current—high-volt pulsed current (HVPC) and low-volt pulsed current (LVPC).
Monophasic HVPC provides a short pulse duration (5-20 μs)5 and high voltage (75- 150 V),7 making ES delivery comfortable while decreasing the risk of skin damage from ion shifts typically associated with other monophasic modes of delivery. The short duration, high-peaked waveform decreases skin resistance so that current can penetrate into deep tissues without causing discomfort.5 HVPC has the most support in published literature for use in tissue healing43
Low-volt devices offer either monophasic or biphasic waveforms with lower voltage and longer pulse durations compared to high volt. Monophasic delivery offers single polarity selection whereas the biphasic mode offers choice of polarity or delivery of an overall neutral or balanced charge. Neutral net charge delivery is thought to benefit wound healing through the stimulation of local cutaneous nerves, thereby improving blood flow to the wounded area.44 For biphasic LVPC delivery, transcutaneous electrical nerve stimulators or TENS units commonly used in the practice of physical therapy for muscle and nerve stimulation1,5 can be utilized.7
A less commonly used form of LVPC is microcurrent, which has an extremely low amplitude (˜200-300 μA)5 and generates very little perceptible sensation, therefore making this method of ES an option for patients who may find other modes of ES uncomfortable. Sussman5 expresses concern about low amplitudes and their ability to overcome tissue resistance with electrode placement on periwound skin. Microcurrent is typically administered via standard ES units; however, there is a relatively new broad spectrum antimicrobial (silver) wound dressing that generates low-voltage current without the need for external power or lead wires. Procellera (Procellera Advanced Bioelectric Technology, Vomaris Innovations, Inc, Chandler, AZ) with Prosit technology is a flexible, bioelectric dressing embedded with flat microcell batteries that produce a sustained low-level current (2-10 mV)7 along the surface of the dressing once it becomes wet with wound fluid or saline (FIGURE 14-9).45,46 At least one source reports that this dressing may perform similar to the body’s own current of injury when in contact with the wound surface.47 The dressing is thin, flexible, and may be cut to size without impeding function.47,48 While positive case–based research on this form of ES delivery appears in the literature,48 strong evidence regarding its use is lacking at this time.
Direct and alternating currents Types of electrical currents are as follows: direct, sinusoidal current, pulsed current, monophasic waveform, biphasic waveform.
Low-volt pulsed frequency dressing Example of a flexible, bioelectric dressing embedded with flat microcell batteries that produce a sustained low-level current (2-10 mV)7 along the surface of the dressing after it is wet with wound fluid or normal saline solution. The dressing is fenestrated to allow escape of fluids; however, it is not recommended for wounds with moderate to heavy exudate. The dressing also has silver ions embedded for antimicrobial action, and it can be cut to the shape of any flat superficial wound. A good indication for the use of this dressing is a wound that is granulated with flat edges to facilitate epithelial migration.
Although not approved for use in the United States, stochastic electrical noise has recently received attention as a possible new form of ES for wound healing.22 Approved for use on chronic wounds in Europe, Canada, and Australia, stochastic electrical noise utilizes low-frequency and low-voltage electrical currents to stimulate sensory nerves in and around the wound area.11,22 A recent study by Ricci and Afaragan11 showed significant reductions in wound surface area in long-term chronic wounds with stochastic noise intervention.
Electrical stimulation is applied to wound tissue by either direct or indirect (also called straddling or periwound) placement of electrodes.20,38 In the direct method, the primary or treatment electrode set for the desired polarity is placed directly in the wound bed (FIGURE 14-10). In order to ensure good contact between the electrode and all surfaces of the wound, saline moistened gauze is commonly used as the electrode. Moist gauze conforms easily to irregular wound surfaces and can be wicked into tracts, tunnels, and areas of undermining so that electrical current can be distributed to all areas of the wound surface. The electrical charge is transferred from the lead wire to the gauze electrode via an alligator clip and a small piece of aluminum foil positioned so that the clip/foil attachment do not come in contact with wound or periwound tissue. (Note: If the clip or foil touch the skin, the patient may experience a burning or painful sensation.) This method is also referred to as “monopolar” because there is only one treatment or active electrode.20
Direct method of applying electrical stimulation
For small wounds, the open area can be filled with hydrogel and the treatment electrode placed over the wound in direct contact with the hydrogel.21 This method of application requires full contact between the electrode and hydrogel. Once the wound is filled to the level of intact skin, the electrode is gently placed over the wound to prevent the gel from being displaced onto the periwound skin. With this method, the treatment electrode must be of sufficient size to cover the wound opening and adhere to periwound skin.
In order to form a complete electrical circuit, ES applications require at least one treatment or active electrode and one dispersive electrode. Placement of the dispersive electrode (sometimes referred to as the return electrode) is debatable and a recent review by Sussman5 resulted in various recommendations with no one strategy shown to be the most beneficial. Since current flows between electrodes, the author suggested that the placement of the dispersive pad be routinely changed so that current flow patterns between the electrodes can be altered and specific areas or tissues targeted.5 Generally, dispersive pad placement over muscle tissue is desirable since this tissue has a high fluid content and therefore low impedance to electrical current. Tissues with low fluid content, such as bone or callus, are not good conductors and as such, skin overlying superficial bones and skin with callus are not desirable locations for dispersive electrodes. When treating a foot or lower leg wound with ES, it has been recommended that the dispersive electrode be placed over intact skin on the thigh. For clear division of polar effects, the dispersive electrode is commonly placed 15 to 30 cm away from the wound site (FIGURE 14-11).5,38 Since depth of current penetration increases as distance between treatment and dispersive electrodes increases, depth of target tissues is taken into consideration in electrode placement.14 (FIGURE 14-12) The presence of necrotic tissue in the wound must also be considered when placing electrodes because the high resistance of nonviable tissue can reduce or alter the flow of electrical current from potentially targeted tissues.30,32,49 Debridement of nonviable tissue prior to ES application will help optimize treatment outcomes.
Placement of the electrodes to allow flow of the current to deep wound bed For this wound, the carbon and gauze electrodes are used in the direct method for a deep wound on the calf. The dispersive electrode is placed on the lateral thigh, allowing the current to flow through muscle and subcutaneous tissue, and at a distance that will facilitate flow of the current to the deeper wound bed.
Placement of the electrodes to facilitate flow of the current to superficial wound bed The wound on the calf of a patient with spinal cord injury is shallow and the surrounding area has atrophied muscle and little subcutaneous tissue. Therefore the dispersive electrode is placed closer to the wound so that the current will flow to the superficial wounded tissue.
Charge density is a consideration when selecting dispersive electrode size. The dispersive electrode is approximately two times the size of the treatment electrode to ensure unidirectional current flow to the target tissue. This also distributes the return current across a larger surface area, thereby improving comfort and reducing the risk of skin irritation under the dispersive electrode. Dispersive electrodes may be carbon or gel, or if larger sizes are needed, may be created using a combination of premade electrodes and moist sponge cut to the desired size. (FIGURE 14-13)
Improvised dispersive electrode Dispersive electrodes can be a combination of carbon and gauze, aluminum foil and gauze, or large gel pads, and are at least twice the size of the active electrode. All electrodes need to have good contact with the skin and wound surface for both comfort and conductivity. They can be anchored with tape or self-adhesive bandages.
The indirect, periwound, or straddling technique uses a bifurcated lead wire and two active, same-polarity electrodes that are placed on opposite sides of the wound (eg, 3:00 and 9:00, 12:00 and 6:00) and can be beneficial on small or large wounds that do not accommodate one electrode (FIGURE 14-14).5 The dispersive electrode is placed the same as with the monopolar technique. With two treatment electrodes, this method of ES delivery is also referred to as a “bipolar” application.20 With this treatment technique, wound tissue is not covered with a treating electrode therefore, saline moistened gauze is placed in the wound bed and the area covered with an insulating dressing or dry towel so that wound tissues are kept moist and protected from hypothermia during the treatment session. Since current is directed between the treatment electrodes, strategic placement is based on wound needs and treatment goals. One concern with this application technique is that when treatment electrodes are placed on intact skin, the current must travel through nonhomogenous tissues (fat, muscle, blood vessels, etc) and due to varying resistance among those tissues, current flow between electrodes and into the wound can be reduced.49 A recent study33 using the periwound technique reported improved blood flow at wound edges with biphasic current versus monophasic current but neither current demonstrated increased blood flow at the center of the wound even though the electrodes were placed directly across from each other on opposite sides of the wound. Some studies suggest benefits using up to four electrodes to improve current flow through the wound bed;30,33 however, currently the direct, single treatment electrode method of ES application is best supported in published literature.14
Straddling or indirect method of applying electrical stimulation The straddling or indirect method of applying ES uses two smaller electrodes on opposite sides of the wound and a larger dispersive electrode, placed 15-30 cm away, over soft tissue that will optimize current flow. Note that the dispersive electrode is placed over the paraspinal muscles and not directly over the vertebrae.
Isseroff and Dahle22 report that the determination of a single ideal approach to determining parameters is impossible because of the extensive variation in the parameters used in published studies. However, Kloth and Zhao7 recommend selecting parameters that provide an overall ES dose between 250 and 500 microcoulombs (μC) per second for safe and effective treatment (TABLE 14-7). Once a decision on mode of application has been made, direct parameter choices include voltage, polarity, pulse duration, pulse frequency, and overall frequency and duration of treatment.
||Download (.pdf) Table 14-7
|Type of ES ||Recommended Parameter Ranges |
|HVPC || |
|LVPC || |
30-35 milliamps (mA)
128 pps initially, can decrease to 64 pps after significant improvement
132 μs pulse duration
45-60 min, 5-7 days per week7
For sensate patients, ES voltage (sometimes referred to as intensity) is typically increased until the patient feels a comfortable tingling under the electrodes. For patients with impaired sensation in the target area, voltage is set just below a visible muscle twitch.38 In patients with concomitant motor and sensory impairment in the treatment area, electrodes may be placed on an uninvolved area elsewhere on the body to establish estimated threshold levels.14 All patients should be monitored closely, especially during the first treatment. If skin irritation occurs under electrodes, voltage should be reduced.
At one time it was recommended that charge selection be based solely on the idea that opposite charges attract and that polarity be set and maintained depending on the charge of the primary target cell. Today, initial polarity is still selected for either positive or negative charge depending on which specific cell is being targeted,50 however, recent research supports the switching of polarity every 3 days (or weekly) to avoid healing plateaus and to maintain progression of healing.14,19,21,50 Overall, wound response guides adjustment of polarity and providers must use clinical judgment as to when shifts in polarity need to occur.
Pulse Duration and Frequency
As mentioned previously shorter pulse durations are typically more comfortable and cause less potential for skin irritation under electrodes. Typical pulse duration is set between 20 and 132 microseconds (μs) depending upon the method of delivery and the ranges available on specific ES units. Pulse frequency ranges from 100 to 128 pulses per second (pps).7
ES is typically set for 45 to 60 minutes a day for 5 to 7 days a week7; however, for patients being treated in outpatient settings, this frequency may not be practical. In this case, outpatients may be treated two to three times per week. After a treatment plan has been established, some patients may be able to administer ES therapy at home20 to accommodate daily treatment recommendations. Some portable ES units allow for locking in parameters for patient safety and are ideal for home use.