INTRODUCTION

Electrocution may occur by contact with high-voltage or low-voltage electrical sources or by a lightning strike. It is generally accepted that chewing through household electrical cords is the most common cause of electrocution in dogs and cats. From 1968 to 2003, a database from several institutions* recorded that 280 dogs and 92 cats sustained electrical injuries. Of these, 54 dogs and 26 cats had chewed electrical cords, and 4 dogs and no cats were identified as having been struck by lightning. It is likely that many of the unspecified electrocutions were low-voltage injuries from chewing household electrical cords.

MECHANISM OF ELECTRICAL INJURY

The mechanisms of electrical injury are related to the direct effects of the electrical current and the transformation of electrical energy to heat. The electrical current may disrupt electrophysiologic activity, leading to muscle spasms, cardiac arrhythmias, loss of consciousness, and respiratory arrest.^1-3 Direct cellular injury may occur through the process of electroporation. Electroporation is the development of momentary holes in cellular membranes induced by electrical shock. The holes allow passage of macromolecules across membranes, causing osmotic damage to cells.⁴

As electrical current is transformed to heat, intracellular and extracellular fluids may become superheated, resulting in coagulation of tissue proteins, thrombosis of small vessels, and degenerative changes in small arterial walls.^1,2,4 Ultimately, the result is necrosis of the superheated tissues and those tissues that become ischemic from the vascular consequences. Direct thermal injury may also occur from arcing of a current that leaves the electrical source, crosses an air gap, and strikes tissue.¹

The severity of electrical injury varies depending on the electrical resistance of the part of the body that is struck, the nature of the current (alternating versus direct), and the intensity of the current (amperage).^1,4 Less energy will be transferred to areas of the body that have high resistance to electrical flow. Dry skin has high resistance; therefore less energy will be transferred in dry skin than in wet skin. Wet skin and moist mucous membranes have low electrical resistance; therefore one can expect high flow of electricity in these tissues and propensity for maximal tissue damage.

Alternating currents tend to cause more severe injury than direct currents at the same amperage. Higher exposure may occur with alternating current electricity than with direct current because the former elicits muscular contraction that prevents the victim from releasing the power source. As such, the exposure time is typically longer with alternating current than with direct current. Direct current electricity does not usually cause muscular tetany.

Given the same resistance, high-voltage electricity can be expected to cause more damage than low-voltage electricity. One might expect more injury from 240-volt outlets used for large household appliances than with 120-volt standard wall outlets. However, current (amperage) is a function of voltage divided by the resistance; therefore the magnitude of the current will depend on the affected tissue as discussed previously.^1,4

PREDISPOSITION TO ELECTRICAL INJURY

Young dogs and cats are the most common victims of electrical injury because they are more likely to chew on electrical cords than are older animals. The average age of dogs with electrical injury has been reported to be 3.5 months (range, 5 weeks to 1.5 years; n = 29); the range of age for seven cats was reported to be 2 months to 2 years.¹ From 1968 to 2003, a database collected in several institutions* revealed that the most common age range for electrical injuries was 2 to 12 months; 186 of 280 (66%) dogs and 44 of 92 (48%) cats with electrical injuries and 38 of 54 (70%) dogs and 12 of 26 (46%) cats that sustained electrical injury from chewing electric cords were 2 to 12 months old. Seasonal predisposition is generally accepted, but there is some difference in opinion as to what time of year most injuries are seen. Holiday seasons characterized by use of decorative lights (Halloween, Christmas) certainly pose electrical risks,⁴ but one study reported that 79% of canine cases occurred during the 6 months from March through August.¹

CLINICAL FINDINGS

Surface burns may be noted at the point of contact with the electrical source. The thermal injury may be superficial, characterized by mild hyperemia, or may manifest as a severe full-thickness burn. Burns from chewing electrical cords have been noted on the lips, gums, tongue (Color Plate 159-1), and palate.^1-6 Some oral cavity electrocutions produce enough trauma to cause dental fractures and oronasal fistulas.⁶

Cardiac arrhythmias may be present, the severity of which depends on the intensity of the electrical current. Sudden death from electrical shock is likely due to ventricular fibrillation caused by low-voltage current, as with most household exposures.^4,5,7 High-voltage exposure may cause asystole.⁴ Animals that survive the initial shock may experience ventricular arrhythmias. Ventricular or sinus tachycardia may be noted on presentation.

Respiratory distress is a common clinical feature noted in the form of tachypnea, cyanosis, orthopnea, coughing, or apnea. Respiratory arrest from tetanic contractions of respiratory muscles occurs during contact with the electrical source, but breathing typically resumes when the victim is separated from the source of electricity.⁸

Causes of respiratory distress include facial or nasopharyngeal edema, diaphragmatic tetany, and neurogenic pulmonary edema. Neurogenic pulmonary edema is a form of noncardiogenic pulmonary edema in which central nervous system (CNS) insult results in massive sympathetic outflow that causes pronounced vasoconstriction and systemic hypertension. As a consequence, there is marked elevation of left ventricular afterload and decreased left ventricular stroke volume, which causes blood to accumulate in the pulmonary circulation, resulting in increased pulmonary capillary pressure and subsequent edema.⁹ The typical radiographic pattern is alveolar infiltration of the caudodorsal quadrant (Figure 159-1).

Figure 159-1 Lateral (A) and ventrodorsal (B) thoracic radiographs of a puppy that was electrocuted by chewing an electrical cord. Note the prominent infiltration of the caudodorsal lung fields. (Courtesy Dr. Everett Aronson.)

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