Electrical and Lightning Injury



Electrical and Lightning Injury


Christopher Zammit

Edward (Mel) J. Otten



INTRODUCTION

Electrical injuries (EI) and lightning strikes (LS) have been reported to cause a variety of neurologic injuries. Interestingly, although some of the associated neurologic sequelae are seen acutely, others develop in a delayed fashion. Although both EI and LS produce injury via the creation of an electrical current, the neurologic complications of each can be quite different.

Low-voltage electrical injuries (LVEI) are defined as resulting from exposures of less than 1,000 V, whereas greater exposures are termed high-voltage electrical injuries (HVEI). They are to be further distinguished as being the result of a direct current (DC) or alternating current (AC), with the latter producing approximately three times as much injury as the former. LS are exceptionally brief, with voltages on the order of the millions, and produce a unique constellation of immediate and delayed injuries.


EPIDEMIOLOGY

The first death in the United States related to an artificial electrical source occurred in front of a crowd in Buffalo, New York in 1881 when an intoxicated man came into contact with a generator. His death was seen as being quite painless, leading to the use of electrocution as a humane method of capital punishment. Formal reporting of electrical and lightning injuries is not required, limiting the accuracy of existing epidemiologic data.

There are an estimated 3,000 EI per year in the United States, including 1,000 deaths. Children are more likely to suffer LVEI, whereas adolescents and adults more commonly experience HVEI, which are frequently occupationally related.

Over 15,000 police departments across the United States use conducted energy weapons (CEW), such as stun guns and TASER devices to restrain suspects. Cardiac arrests have occurred after the uses of CEW, but a causational link has been proposed in only a minority of cases. In the majority of circumstances, excited delirium and/or intoxicates ingested by the victim are blamed for causing the arrest.

Three hundred to 1,000 lightning injuries occur per year in the United States, with an estimated mortality rate of 10%. Many victims either do not seek care at the time of the injury, and half of the immediate deaths are transported directly to the coroner and never reported. Victims are usually men (4.5:1 male-to-female ratio) in their second to third decade of life and are performing outdoor recreational or occupational activities.


PATHOBIOLOGY


ELECTRICAL INJURIES

The severity of LVEI is subject to the pathway of the current and proportional to the duration of exposure and amount of current (milliamperes [mA]). Low-voltage AC, in contrast to low-voltage DC, can produce continuous involuntary muscle contractions. If the victim grips an AC electrical source with their hand, tetany of the flexors of the upper extremity prove stronger than the extensors, causing the victim’s grasp of the source to be strengthened. Currents of 6 to 9 mA or greater, which can be achieved via exposure to a standard 110-V household outlet, exceed the “let-go threshold,” rendering the victim incapable of dissociating himself/herself from the source. If the current flows through the thorax, tetany of the muscles of respiration can occur, causing the victim to suffocate. Currents of approximately 50 to 100 mA can cause ventricular fibrillation; the current threshold is inversely proportional to the duration of exposure.

Direct contact with a high-voltage electrical source more commonly produces diffuse, sudden, and violent muscle contractions that thrust the victim away from the source, causing traumatic insults in addition to the EI. Even with brief exposures, the high voltages convey a tremendous amount of energy, which is released via electrothermal heating at points of high resistance (e.g., the skin, where full-thickness burns are seen). Internally, the current is carried along tissues of low resistance, such as the nerves, muscles, and blood vessels. Immediate effects include muscle necrosis and small-vessel thrombosis, resulting in threats to extremity viability and peripheral nerve integrity through compartment syndromes and limb ischemia.

In contrast to a direct contact injury, a spark can jump from a highly charged source to a ground source, forming an electrical arc, where temperatures can reach 2,500°C. When a victim is caught in the path of the arc, he or she suffers cutaneous thermal burns and blast injuries when the suddenly heated air rapidly cools, in addition to a HVEI by becoming part of the conduction pathway of the current.

CEWs are reported to be high voltage (with an initial charge of ˜50,000 V). However, the victim does not experience this voltage. Instead, it allows for an arc to be created if the barbs do not make contact with the skin, which happens about 30% of the time. Once contact is made, the voltage immediately decreases to provide a current of approximately 2 mA in brief pulses at a rate of 20 times per second, producing involuntary muscle clonus (much like an AC circuit), preventing the suspect from resisting. Because of the low current, EI is rare with CEWs, and most injuries, when they do occur, are traumatic and related to when the victim falls to the ground.


LIGHTNING STRIKES

Lightning victims can be directly struck with the discharge, receive current via an adjacent object that was directly struck (side flash), become part of the ground current when their feet are apart (step voltage), be the conduit for currents that originate from the ground and discharge toward the clouds (upward stream), and/or experience a concussive or blast injury from the rapid heating and cooling of the air (thunder). Curiously, some of the injuries typically seen with direct contact HVEI are not found in lightning injuries and entry and exit wounds are only seen in a minority
of cases, suggesting that most, if not all, of the current flows external to the victim. This is thought to result in a powerful magnetic field being created over the victim, causing electrical currents to flow internally through low-resistance tissues (i.e., nerves, muscles, blood vessels), resulting in powerful muscle contractions and medullary dysfunction leading to apnea, asystole, and a tremendous catecholamine surge.

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Jul 27, 2016 | Posted by in NEUROLOGY | Comments Off on Electrical and Lightning Injury
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