Electrical Injuries

Introduction

The harnessing of electricity may be the technical advance with the greatest impact on human life and culture in recorded history. The tools of modern life are increasingly powered by electricity, and life without it would be unrecognizable. There is, however, a price to be paid for this advancement. Electrical burn injuries are estimated to make up several thousand admissions to burn centers each year in the United States. The American Burn Association (ABA) 2016 Burn Incidence Fact Sheet, which is composed of registry statistics compiled by ongoing national health care and fire casualty surveys and the National Burn Repository, estimated 40,000 burn admissions of which 4% had a reported electrical etiology. These injuries are the most devastating of all thermal injuries on a size-for-size basis and are the most frequent cause of amputations on the burn service. These injuries are distributed in a bimodal fashion in regards to age. Work-related injuries are seen most commonly in adults. Together, electricians, power company linemen, and crane operators are especially at risk. Exposure to electricity made up 3% of all work-related deaths in 2013–2014 according to the United States Department of Labor; Bureau of Labor Statistics. There is a 2 : 1 male-to-female ratio in childhood, but more than 90% of electrical injuries in adults are in men. Children are more commonly injured in accidents in and around the home. Children younger than 6 years are more likely to encounter low-voltage outlets or electric cords. Older children have an increased incidence of high-voltage injuries by comparison because of their increased mobility and adventurousness.

Electrical burn injuries have several unique acute manifestations that differ from other thermal injuries and require expertise in management. Decisions must be made early regarding cardiac monitoring and emergent or urgent exploration and decompression for compartment syndrome, as well as a more complex fluid management strategy to avoid the complications of acute kidney injury associated with myoglobinuria. These patients may need access to other specialty services such as plastic surgery consultation for possible early flap coverage to protect potentially viable tissue. In addition, physical medicine and rehabilitation services, with experience caring for patients with electrical injuries, are simply not available in nonburn centers. These injuries benefit from the multidisciplinary team approach and vast experience typically seen at ABA-verified burn centers.

Pathophysiology

Electrical current passing through tissue can cause injury by multiple distinct mechanisms. These include the direct action of electrical forces on proteins, cell membranes, and other biomolecular structures, as well as tissue injury mediated by the generation of heat. The severity of injury is multifactorial and determined by voltage, current (amperage), type of current (alternating or direct), path of current flow, duration of contact, resistance at the point of contact, and individual susceptibility. These burns are somewhat arbitrarily classified as low (<1000 V) and high voltage (≥1000 V). Although the low-voltage injuries are generally more localized to the area of the contact point, the high-voltage injuries may be associated with both extension into deep tissue as well as a spreading out phenomenon to surrounding structures. So, although a low-voltage injury may penetrate deeper structures, the zone of injury is more limited. In contrast, high-voltage injuries, somewhat resembling crush injuries, tend to demonstrate a “tip of the iceberg” phenomenon, extending into deep structures (muscle or bone) as well as spreading out proximally and distally beneath the contact point. The clinical implications of this will be discussed later, but from the surgeon's point of view, these injuries are potentially more urgent and occasionally emergent, but low-voltage injuries are not.

Domestic wiring in the United States operates on alternating current (AC) at 120 V. Therefore, nearly all burns occurring indoors are of the low-voltage type. Coworkers typically witness high-voltage injuries occurring indoors because these are more common in industrial or factory settings.

Unlike voltage, the actual amount of current is unknown. Current flow is related to the voltage by Ohm's law where:

Animal experiments have demonstrated that resistance varies continuously with time, initially dropping slowly then much more rapidly until arcing occurs at the contact sites. Resistance then rises to infinity and current flow ceases. Temperature measurements taken simultaneously showed that the rate of temperature rise parallels changes in amperage. Interestingly, tissue temperature, a critical factor in the magnitude of tissue injury, does not increase distal to the contact points. Clinically, it is common to see relatively normal and intact digits in association with devastating tissue damage at the wrist and forearm that ultimately results in amputation at the forearm level. Early and detailed discussion between the surgeon and patient and family can avoid confusion if the patient progresses to amputation.

In North America, the majority of all electricity used and the burn injuries it causes are the result of 60 cycle-per-second commercial AC, which reverses polarity 120 times per second. Exceptions where direct current (DC) is used for power are seen in industrial settings, as well as computers, light-emitting diodes (LEDs), solar cells, and electric vehicles. A series of events in American history, known as the War of the Currents, explains the dominance of AC over DC. Contributions from notables such as Thomas Edison, Nikola Tesla, and George Westinghouse led to concerns over commercial competition, electrical safety, and debates associated with the introduction of the electric chair. The degree of sordid detail surrounding these events can make for interesting tangential information during resident and medical student teaching sessions.

Given the nature of AC and its rapid reversal of polarity and the relative inability to reconstruct the history with accuracy, the terms entrance and exit wounds are inaccurate and should be used with caution if at all. The term contact point is more appropriate. A thorough search for contact points should occur in all patients with electrical injuries because they may be few or many, obvious or well hidden (e.g., in the hair line).

The path of current, although often imprecise, can make a significant difference in outcome. Current potentially traversing the conduction system of the heart or a pathway including the central nervous system can alert the clinician to potential complications. AC causes tetanic muscle contractions, which may either throw the victim away from the source or draw him or her into a continued contact known as the “no-let-go” phenomenon. This occurs because both forearm flexors and extensors are stimulated by the current flow, but the flexors overpower the extensors, making the person unable to let go voluntarily. Given that humans most often explore their environment by grasping rather than tapping with the back of the hand, contact is usually prolonged. Altered levels of consciousness reported in about half of high-voltage victims also contributes to prolonged periods of contact. Resistance, measured in ohms, at the point of contact varies from approximately 100,000 ohms for heavily calloused hands or feet during very dry winter weather to less than 2500 ohms when skin is damp.

The classification of electrical injuries from a clinical point of view comes in four varieties: (1) the true electrical injury caused by the flow of current, (2) an arc injury resulting from the electric arc generated as the current passes from the source to an object, (3) flame injury caused by the ignition of clothing or surroundings, and (4) lightning strikes.

Electricity arcs at temperatures up to 4000 ° C and causes a flash-type injury without actual current flow through the body. This is most commonly seen in electricians working with metal objects in close proximity to an electrical source. The victim may be thrown by the force and sustain trauma, including ruptured eardrums and any other variety of blunt force injuries. These injuries that occur without actual current flow may be classified like any other flame injury. However, the potential problem that arises is in the difficulty in ascertaining whether there was actual flow of current. As a result, most of these patients will be treated as having true electrical injuries.

The mechanism of electrical injury appears to be a multifactorial combination of thermal and nonthermal causes. Electricity flowing through tissue generates heat. Electrical current via ohmic conduction leads to Joule heating that can cause severe burn injury to the victim. The burn injury is the result of damaging supraphysiological temperatures, which affect all proteins and cell membranes with Joule's law defining the amount of power (heat) delivered to an object:

In increasing magnitude, tissue resistance is lowest from nerves, blood vessels, muscle, skin, and bone. Theoretically, current flow would be distributed in proportion to resistance, with tissues having the highest resistance generating the most heat. However, in animal models, the body tends to act as a single uniform resistance rather than a collection of different resistances. In other words, the body acts as a volume conductor, with the severity of injury being inversely proportional to the cross-sectional area of the involved body part. Clinically, this is observed in particularly severe injuries at the level of the wrist and ankle. Deep tissue does appear to retain heat such that periosseous tissue, especially between two bones, will often have a more severe injury pattern than more superficial tissue. Clinically, this may be seen during exploration of the forearm wherein the superficial flexors are clearly involved and injured but the deeper pronator quadratus muscle appears to have a more severe injury. The associated macro- and microvascular injury appears to occur at the time of injury and is irreversible. This vascular injury has been studied in a rabbit model in which optical microscopy demonstrated severe injury to blood vessels. Necrosis of vascular walls and thrombosis with destruction of arterial endothelium, pyknosis of vascular smooth muscle, and fibrinous exudates accompanying the thrombotic changes were noted. Progressive muscle necrosis over the first 72 hours after injury was also observed and thought attributable to vascular injury. The study period followed the injury pattern for only 72 hours, but experienced clinicians can attest to a longer period of progression that may extend more than a week. These findings as well as clinical experience argue in favor of serial debridement and a conservative approach to definitive grafting. The pathophysiology, although not completely understood, also includes electroporation and electrochemical interactions in addition to thermal interactions. These affect all tissue components, but the cell's plasma membrane appears to be the most important structure in determining the rate and quantity of tissue injury accumulation. Electroporation is the formation of aqueous pores in lipid bilayers exposed to a supraphysiologic electrical field. The formation of these pores allows calcium influx into the cytoplasm and triggers a subsequent cascade leading to apoptosis. Particularly interesting, owing to characteristics of electric fields, it has been shown that cells of long length (skeletal muscle and nerve) are more vulnerable to electroporation. Further experimental work by Block et al. in a Sprague-Dawley rat model confirmed that nonthermal effects alone could induce cellular necrosis. Electroconformational denaturation of transmembrane proteins refers to the changes in polarity of amino acids in response to exposure to electrical fields. Experimentally, voltage-gated channel proteins were found to change their conductance and ion specificity after exposure to a powerful pulsed field.

Acute Care

Electrically burn-injured patients present some unique challenges in the acute setting. There are essentially three acute management concerns differentiating these patients from patients who were thermally injured without flow of electric current. In addition to the application of the basic principles of Advanced Trauma Life Support (ATLS), the three issues that need to be addressed in the “golden hour” are (1) which patients require electrocardiographic monitoring and for how long; (2) which patients are at risk for compartment syndrome and may need emergency surgical intervention (sometimes directly from the emergency department [ED]); and (3) how fluid resuscitation should proceed in the light of the preponderance of deep tissue injury that may not be appreciated on physical examination, particularly in the presence of pigmented urine.