Household Electrical Injuries
By David J. Karras, MD
Electrical injuries are notorious for their profound multisystem injuries. These devastating traumatic events, familiar to most emergency physicians, generally result from high-voltage electricity. Most electrical injuries presenting to the ED, however, are due to low-voltage electrical exposures, usually defined as less than 1000 V. The vast majority of ED encounters with electrical injuries, in fact, are related to household electricity, which is usually 110-220 V. While low-voltage electrical injuries are far less likely to result in severe morbidity and rarely require hospitalization, occult or delayed injury is still possible; thus, evaluation is often problematic.
Mechanics of Injury
The destructive potential of electricity can be described by Joule’s law, in which heat production is proportional to current (amperage), tissue resistance, and duration of exposure. None of these factors, however, can usually be accurately determined. Electricity is delivered at a fixed voltage, rather than a fixed current; resistance of human tissues is highly variable, and duration of exposure can only be approximated. The alternating current delivered to households generates more heat and hence greater injury than does direct current.
The effects of current vary widely over a narrow range: exposure to a 1 mA current can be detected as tingling, while tetanic muscular contractions may result from 6-9 mA exposure and as little as 4 mA exposure in children. The skin of the hands and feet has relatively high resistance and therefore may sustain dramatic thermal injuries from current conduction. Water on the skin surface reduces cutaneous resistance, decreasing the risk of superficial burns but greatly increasing the risk of internal injuries. Because of their low resistance, muscle and neural tissue conduct a great deal of current and may sustain enormous injury, including extensive myonecrosis and cardiac or respiratory arrest. The flow of current through the body, and therefore the pattern of injury, is extremely unpredictable, and injuries to almost all tissues and organ systems have been described in the literature. These systemic injuries are far more common in high-voltage than in low-voltage electrical exposures.
ED Presentations
Most household electrical injuries, and about half of all electrical injuries presenting to the ED, involve children.1 The majority of these children are pre-school-age, particularly toddlers between the ages of 1 and 3 years, who sustain injuries either from insertion of metal objects in wall sockets or placement of electrical cords in the mouth.2 Two reviews of many years’ experience with electrical injuries at children’s hospital EDs found that the vast majority of patients sustained minor electrical injuries.1,2 About one-fifth of patients had sustained shocks and had no signs of injury at all. Most, however, presented with isolated burns, all less than 1% body surface area and equally distributed between first, second, and third degree. A "minor" burn is not necessarily one without sequelae: about 15% of children had burns of the oral commisures, often requiring hospitalization and long-term follow-up. Complications among patients with burns to other areas of the body were very uncommon. Less than 10% of household electrical exposures represented major injuries, and all of these resulted from bathtub electrocutions. Those with major electrical injuries developed profound complications including cardiopulmonary arrest, seizure, severe burns, and severe rhabdomyolysis.
Much of the literature on assessment of patients with electrical injuries cites case reports of patients having sustained high-voltage exposures. Unqualified recommendations that all patients with electrical trauma be referred to burn centers or at least observed as inpatients are common and may be unsubstantiated. In fact, the majority of patients with electrical injuries have sustained minor injuries and do not require extensive evaluation.3 Assuming that the ABCs have been addressed and that the patient is hemodynamically stable, the first step in assessing a patient with household electrical injuries is to determine the source of the injury. Discharge of capacitors found in electronic equipment can expose the patient to a higher voltage than would usually be expected in household injuries.4 In general, however, most household electrical exposures can be assumed to be low-voltage injuries.
Assessment and Treatment
A history of loss of consciousness, ischemic chest pain, hypoxia, or objective neurological deficit mandate hospitalization with electrocardiographic monitoring. In addition, a CT of the head may be indicated for patients presenting with or complaining of neurological deficits, as intracranial injury is well-described as a result of electrical exposure. Electrical exposure while immersed in water should not be considered a low-risk injury and probably warrants inpatient attention regardless of complaints or physical findings.
A careful examination should be performed and any cutaneous burns noted. Small, isolated burns are typical of low-voltage electrical exposure, while extensive or multiple burns suggest more significant exposure. Burns to the head may be more likely to have sequelae (such as cataract formation) than extremity burns.4 The neurological examination should be normal and remain so during the period of observation.
Laboratory testing to exclude inapparent systemic injury is warranted in all electrical injuries, although recommendations for the extent of testing vary considerably. There is agreement that all patients should receive an electrocardiogram and have their cardiac rhythm monitored for 4-6 hours while in the ED. Abnormalities in the ECG or dysrhythmias require hospitalization for cardiac monitoring and to rule out infarction even in asymptomatic patients. There is also agreement that the urine should be checked for the presence of heme pigment, which would suggest significant rhabdomyolysis and the risk of renal failure if untreated.
Some authors suggest that routine serum chemistries, creatine kinase (CK) total and CK-MB fraction, and complete blood count be performed on every patient with electrical trauma to rule out occult injury.3,5 Although widely disseminated, these recommendations appear to be unsubstantiated. It has been shown that elevations in CK-MB are very common following electrical injury among patients with no other evidence of myocardial injury, and that skeletal muscle injured by electricity produces and releases unusually high levels of CK-MB.6 In light of this information and without any evidence to the contrary, it does not appear to be useful to use the CK-MB to "screen" patients with low-risk electrical injuries.
Patient Disposition
After a history, examination, limited laboratory testing, and a period of observation with cardiac monitoring, a disposition decision can be made based on the risk of significant systemic electrical exposure. A low-risk patient is one having sustained a low-voltage injury, without evidence of corporeal conduction, who is asymptomatic and has a normal ECG, no dysrhythmias, and no urine pigment.4 The examination should be normal except for small and isolated burns. Such patients may be managed with local wound care, tetanus prophylaxis, and follow-up care. Patients not meeting these criteria, despite a history of low-voltage exposure, should be admitted for cardiac monitoring. Extensive or severe burns may require care in a burn specialty unit.
An exception to the excellent prognosis associated with isolated electrical burns is the child with oral injuries, which may result from biting an electrical cord or placing the end of an extension cord in the mouth. Although these appear to be localized injuries, the risk of delayed labial artery hemorrhage and cosmetic or functional compromise from scar formation generally require oral or plastic surgical consultation in the ED. Many of these patients will require admission to minimize long-term complications.
References
1. Garcia CT, et al. Electrical injuries in a pediatric ED. Ann Emerg Med 1995;26:604-608.
2. Baker MD, Chiaviello C. Household electrical injuries in children. Am J Dis Child 1989;143:59-62.
3. Brown BJ, Gaash WR. Electrical injuries and lightning. Emerg Med Clin North Am 1992;10:211-229.
4. Cooper MA, Johnson K. Electrical injuries. In: Rosen P, et al, eds. Emergency Medicine. 3rd ed. St. Louis: CV Mosby; 1992:969-978.
5. Fish R. Electrical shock, part 3. Deliberately applied electrical shocks and the treatment of electrical injuries. J Emerg Med 1993;11:599-603.
6. McBride JW, et al. Is serum creatine kinase-MB in electrically injured patients predictive of myocardial injury? JAMA 1986;255:764-768.
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