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Usually, electrical injuries are arbitrarily categorized into 1 of 3 groups: low-voltage injuries, high-voltage injuries, and lightning injuries (see Causes). Each has its own special concerns.
Pathophysiology: Certain properties of electricity and tissue illustrate the mechanisms of electrical injury and the ability to predict patients' outcomes. These properties include voltage, current, resistance, and conductance. Voltage is the electromotive force or the difference in the electrical potential. The current is the flow of electricity. The resistance of a material is its opposition to the passage of an electric current through it, and its conductance is its ability to transmit a current. In addition, electricity can also form arcs and result in the creation of plasma.
Factors that determine the extent of tissue damage, morbidity, and mortality include the voltage, the type (alternating current [AC] or direct current [DC]) and path of the current, and the resistance or conductance of the tissue (especially the type and quantity of the tissue affected and its degree of hydration, orientation, contact surface area, and duration of exposure).
The larger the voltage for a given conducting body of relatively fixed resistance, the larger the amount of current that can pass through it. Because voltages of generated electricity are usually known (and measured in volts) and because the resistance of the body is not, the current must be calculated.
The inherent safety or injury consideration with low-frequency energy is that it is also within the range of physiologic stimulation of the neuromuscular action potential. Put simply, with a current stronger than 16 mA, the muscles of a portion of the body that is involuntarily transmitting impulses can contract as long as the current is applied. (The threshold of involuntary spasm is called the let-go threshold.) In practical terms, when a person touches his or her hand or forearm to a source of current, the extremity contracts and the person cannot release his or her hand or forearm from the source. This contact prolongs the exposure and thus the potential damage.
Increasing the duration of contact generally increases the tissue damage, at least until the conducting tissue carbonizes and becomes more resistant to further flow of the current. When the body becomes a part of an electrical circuit, the current frequently becomes more concentrated at the entry and exit points (with some exceptions). At these points, greater tissue damage can occur, especially in terms of thermal burns.
This muscular contraction effect, coupled with the increased ability of AC to penetrate the epidermal resistance barrier (see below), explains why lower AC voltages are as dangerous as the higher DC voltages and currents. In fact, at the same voltage, AC is more likely than DC to result in serious injury.
Effects on tissue
In comparison, the phenomenon of electroporation is the more rapid effect of current passing through cellular tissue. This is strictly a cellular (or lipid bilayer) phenomenon resulting from the denaturing effects of the current on the negatively charged proteins in the cell membrane, especially those around the cell pores and gates. The proteins in the cell membrane can lose their 3-dimensional structure and distort or create intramembrane pores or gates. Consequently, intracellular contents can admix with the extracellular components. If not reversed in time, this phenomenon leads to cell death, which is not the effect of joule heating (which takes much longer to occur).
In addition to lightning, step voltage is another high-voltage discharge phenomenon. When an electrical discharge (especially lightning) strikes a grounded surface, the current rapidly dissipates outward in a radial pattern along the surface. The resultant difference in the electrical potential between 2 points, even those separated by a relatively short distance (eg, length of a walking stride between the feet), may be tremendous. The dissipating current can often find a pathway of lower resistance. For example, the current may travel from one leg through the body to the other leg instead of passing along the ground, even though the legs are separated by only a few inches. The result can be devastating when large voltages are involved, as in lightning strikes. Because farm animals have longer strides, this kind of injury is more likely to occur in animals than in people.
Resistance and Conductance
Nerves and blood vessels carry relatively more current with less heat generation, whereas bone tends to convert more of the electrical energy into heat. The difference in conductance is why high-voltage thermal damage has a significant deep component. In addition, because of its large volume, muscle carries the largest amount of current, which also heats the surrounding tissues.
The epidermal barrier is effectively removed when the skin is immersed in a fluid conducting medium such as water. With a fluid conductor, the flow of current is spread over a broader contact surface, and the water and its attendant ions can more effectively reach portions of the epidermis that are better conductors. For this reason, burns are not seen on the surface of skin immersed in water; in addition, more current flows through the body as a whole because the body becomes a whole-volume conductor. The classic example of this phenomenon is bathtub electrocution, which has a high mortality rate because the current can cross the myocardial and diaphragmatic muscles, often without leaving a surface burn of any kind.
When electrodes are applied to the skin, as in cardioversion, a perimeter effect can be seen (Martinez, 2000). Usually, only a first-degree burn occurs at the perimeter, as demonstrated at histologic examination. In this peculiar phenomenon, the applied current passes through the center of the interface between the skin and the conducting pad or gel without causing significant thermal burn. However, the current arcs through the surrounding skin on which little or no conductive gel is placed and where the conducting pad has an abrupt edge. The result is a thermal burn through the less conductive epidermis. This effect has been largely eliminated with the use of electrode pads with a high-impedance perimeter.
AC energy does not meet the same initial resistance in the epidermis because the direction changes in the current act like alternating magnetic fields that induce an electrical field in the tissue. These magnetic fields (similar to those used in MRI) readily penetrate the body (Lee, 1997). Compared with current conduction, current induction does not depend on surface skin resistance.
Arcs and Plasma
The temperature of an arc is 2,500-10,000°C. This resultant temperature can create such a shearing force that the tissue layers frequently separate. The large temperature gradient often results in full-thickness or partial-thickness burns of the skin and deeper tissues. Additionally, the temperature of an arc (eg, lightning strike) can ignite clothing and even melt metal objects (eg, a coin in the pocket), which can then cause secondary thermal injuries. Also, when large amounts of heat are generated (as in a lightning arc), superheating of the surrounding air can generate a thermoacoustic blast (thunder) that can cause blunt injuries.
Plasma, a highly ionized gaseous conductor, can be generated as a result of contact with metal power lines. The result is the formation of a peculiar coating of metal on the skin, or effectively, electroplating of the skin. Plasma can also be generated from within the body at the point at which an arc eventually contacts the body.
The effect of electrical injuries on the US economy is staggering. For occupational injuries alone, the National Institute for Occupational Safety and Health estimated an impact of more than $1 billion on the economy (Lee, 1997). Electrical burns are the fifth leading cause of occupational fatalities (Kennedy, 1998).
As a separate category, lightning injuries cause 300-600 deaths annually in the United States, more than any other weather phenomenon (excluding hurricane Andrew) (Epperly, 1989). In fact, more deaths have been attributed to lightning than to any other natural disaster, and the rates do not take into account the fact that the annual frequency of nonfatal lightning injuries is 3-5 times that of fatal injuries (Cooper, 1997). Furthermore,
many injuries are unreported.
* Internationally: The increasing worldwide incidence of electrical injuries is the result of several factors. The population is growing, as is the percentage of people who use or have access to electricity. Developing nations are particularly affected; for example, one physician in the Dominican Republic noted that as many as 39% of admissions to the local hospital for burns were due to electrical injuries (Browne, 1992). Increased reporting of these injuries also plays a role.
Mortality/Morbidity: In the United States, electrical injuries account for more than 1,000 deaths per year, more than 50% of which are caused by low-voltage injuries. Patients with low-voltage injuries have a disproportionately high mortality rate compared with high-voltage injuries and lightning injuries.
* High-voltage injuries may cause relatively few deaths and relatively more morbidity because the energy involved can cause the individual to be thrown back from the point of contact, or it can cause the violent and sudden single muscle contraction, which also propels the individual away from the electrical source. Also, in patients with high-voltage injuries, the high rate of limb amputations (45-71%) accounts for much of the resultant morbidity.
* Patients with lightning injuries have a mortality rate of less than 30%. Factors that influence this rate may include the flash mechanism of injury (see Pathophysiology) and the lightning standstill phenomenon (see Physical).
* Bathtub electrocution has a high mortality rate because the current can cross the myocardial and diaphragmatic muscles, often without leaving a surface burn of any kind.
Sex: Nonlightning electrical injury has a male predilection approaching 93% that reflects the preponderance of men in construction and electrical occupations. High-voltage injuries are most common in men (Rasmussen, 1990).
Age: Nonlightning electrical injury has a bimodal distribution with respect to age.
* In young people aged 11-18 years, some accidents occur as a result of their touching high-voltage power lines.
* The second large peak occurs in persons aged 15-40 years as they enter or re-enter the workforce.
* If an electrical burn is suggested, certain clues to the type of injury (predominantly findings on the skin surface) may become evident on the secondary physical survey.
* If the history or extent of injury is unknown, a thorough physical assessment of the electrical injury is critical.
Physical: Specific surface-injury patterns may be of great importance in the diagnosis and treatment of patients with electrical burns. If the features of the history suggest an electrical burn, certain clues to the type of injury (predominantly findings on the skin surface) may become evident on the secondary physical survey.
Frequently, an electrical injury of significance, especially one in the extremities, seems more like a crush injury than a burn because the external signs of the injury often overlie a more serious and deeper injury (Kennedy, 1998).
* High-voltage electrical injuries
* Thermal burns
* Lightning injuries
* Low-voltage injuries
Causes: Specific causes of electrical injuries are described below.
* High-voltage injuries
* Lightning injuries involve voltages higher than those of the other injuries, and are usually categorized separately.
* Other electrical injuries
Histologic Findings: Distinct histologic changes may be evident on microscopic examination. Vertical stretching of the basal cells of the epidermis, and sometimes the overlying epidermal cells, can be demonstrated. Dermoepidermal separation may be evident. Elongated, degenerated, cytoplasmic processes may extrude from the basal cell layer into this separation; this finding is sometimes called feathering (Bush, 1987). This extrusion may be the histologic correlate of thermoacoustic forces acting between the layers of the epidermis and dermis, because the current is able first to breach the drier epidermis that produces more heat before reaching the underlying dermis (with more conductive properties).
Because blood vessels are one of the best tissue conductors of electrical current, vascular histologic damage is commonly observed. Although this damage appears to be greatest in the medial layer, intimal injury due to immediate or delayed thrombosis, edema, and coagulation necrosis is also observed. These effects may be mediated by electromechanical disruption of the endothelial membrane, with exposure and eventual cellular disintegration
of the medial cellular layer of the involved vessel.
Medical Care: The type of electrical injury (ie, high-voltage, low-voltage, or lightning injury) may be an important consideration in the treatment and prognosis. In an injury or possible injury of significance, addressing the ABCs first is of paramount importance. Care should be taken not to miss an exit wound or a smaller pathognomonic sign of electrical injury. A secondary survey is critical and must be appropriately thorough.
Emergency service responders may treat the patient at the scene of the injury. After the safety of the responders is ensured, they should attend to the basics of supportive care, and appropriate advanced cardiac life support measures should be administered.
Life-saving measures should be continued at a medical center at which patients with multiple trauma can be treated most appropriately. Optimally, the center should have an adequate burn unit or the ability to treat patients with burns. Secondary assessments are performed here as well.
* With at least 2 large-bore intravenous lines and a Foley catheter in place, parenteral fluid therapy should be administered to maintain a urine output of at least 0.5-1.0 mL/kg/h. However, if heme is present in the urine, urine output of 1.0-1.5 mL/kg/h should be maintained.
* All patients presenting with an electrical injury of more than a minor nature should be treated as if they had multiple trauma. Frequently, an electrical injury of significance, especially one in the extremities, seems more like a crush injury than a burn because the external signs of the injury often overlie a more serious and deeper injury (Kennedy, 1998).
* With electrical burns, serial examinations performed on an inpatient basis best delineate the extent of necrosis, because progressive necrosis of otherwise normal-appearing (but nonetheless irreversibly damaged) tissue is common.
* In a reversal of the usual triage practice, the initiation of earlier and more prolonged resuscitation in persons struck by lightning who become unconscious has saved many lives. Because of our improved understanding of the phenomenon of lightning standstill, health care workers are realizing that individuals struck by lightning can successfully be resuscitated much later than previously believed. Standstill is likened to a state of suspended animation in which cell death does not occur immediately after apparent clinical death. In fact, complete resuscitation is likely even after the patient has been in this state for several minutes.
Surgical Care: Limb-saving measures, such as escharotomy and fasciotomy, may be needed to restore tissue perfusion or to control respiratory expansion of the thorax.
Some high-voltage injuries (especially lightning injuries) are known to cause such localized and complete vasospasm of an extremity that the limb can appear cold and lifeless for hours; however, it eventually recovers completely. Early amputation of such a limb would be disastrous.
* Perfusion to the extremities is paramount.
* If nonviable skin is excised, delaying definitive closure until 1-2 weeks after the procedure or until base viability is ensured is reasonable.
Consultations: Depending on the type of electrical injury and the collateral or secondary injuries, consultation with the following specialists may be needed once definitive treatment is begun.
Diet: In seriously injured patients, as with burn patients, dietary therapy must be commensurate with their grossly increased anabolic needs. Dietary therapy may include parenteral nutrition.
Activity: Because of the possibility of significant deep-tissue injury, eventual therapy (eg, occupational or physical therapy) may become necessary to fully rehabilitate a patient.
The goals of pharmacotherapy are to reduce morbidity and prevent complications.
Further Inpatient Care:
* Outpatient care such as occupational and/or physical therapy may be required, in addition to continuing burn wound care (eg, dressing changes, whirlpool treatments, administration of anti-infective agents).
* As in patients with thermal burns, patients with contractures may require extended outpatient care.
* Previously, low-voltage injuries accounted for a disproportionately high mortality rate.
* Regarding accidents related to outdoor high-voltage power lines, the newer practice of burying power lines will probably decrease the rate of incidental contact with them. Most occupational accidents are preventable with adequate training and precautionary measures.
* If the current technical problems of superconductors are overcome, higher voltages may become available in work and home settings, they may pose new attendant risks absent with the current small-caliber wiring.
* Used more judiciously, lightning detectors of the type usually available only to weather services may help in preventing some lightning strikes. Avoiding high ground, proximity to trees and bodies of water, and staying in an insulated environment (eg, house, car) are helpful in reducing the risk of a lightning injury.
* Short-term and life-threatening complications include cerebral edema, acute tubular necrosis, rhabdomyolysis, and electrolyte imbalances, as well as the usual ABC and perfusion concerns in extensive or circumferential electrical burns.
* Complications may result from electrical burns of the oral commissure.
* Labial artery bleeding is a late complication of oral commissure burns.
* Staining of the teeth is a common delayed effect.
* Primary care providers can also discuss the appropriate preventive measures for low-voltage household-type electrical injuries with parents.
* In lightning-prone areas, the avoidance of tall structures or uninsulated surroundings are topics that are generally understressed in community forums.
* For excellent patient education resources, visit eMedicine's Environmental Exposures and Injuries Center and Burns Center. Also, see eMedicine's patient education articles Lightning Strike and Thermal (Heat or Fire) Burns.
* The failure to perform an appropriately thorough secondary survey may cause exit wounds or small pathognomonic signs of electrical injury to be missed.
* The failure to anticipate labial artery bleeding in an oral commissure burn, a late complication, is a pitfall.
* The failure to teach emergency medical services and emergency department personnel how to recognize the lightning standstill phenomenon is a pitfall.
* The failure to perform serial inpatient examinations may cause the extent of necrosis to be underestimated because progressive necrosis of otherwise normal-appearing (but nonetheless irreversibly damaged) tissue is common in electrical burns.
* The early, unnecessary amputation of a limb is a disastrous pitfall. Some high-voltage injuries, especially lightning injuries, are known to cause such localized and complete vasospasm of an extremity that the limb can appear cold and lifeless for hours; however, it eventually recovers completely.
Information extracted from an article featured here: www.emedicine.com
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