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Electrical and Lightning Injuries


Acknowlegments

The authors wish to acknowledge and thank Kelly P. O’Keefe and Rachel Semmons for their valuable contributions, expertise, and authorship of this chapter in previous editions.

Key Concepts

  • Electrical current follows the path of least resistance, which is often along neurovascular bundles. Deep tissue injuries and organ damage are often more extensive than indicated by examination of the overlying skin.

  • Testing is not indicated for victims of low-voltage electrical injuries who are asymptomatic or have minimal local symptoms and physical evidence of burn injury. These patients may be discharged home after emergency department (ED) evaluation.

  • Patients exposed to high-voltage sources or lightning strikes who present with syncope, altered mentation, focal neurologic abnormality, significant burns, entry and exit wounds, or persistent symptoms should have testing including electrocardiography, complete blood count, basic chemistry panel, myoglobin and troponin level determination, and urinalysis. Additional testing is directed at suspected areas of injuries.

  • Patients with electrocardiographic signs of cardiac injury or dysrhythmias, or with evidence of significant local injury, should be monitored for 12 to 24 hours in the ED, observation unit, or inpatient setting.

  • The enormous current of a lightning strike may cause critical injury or death, or the current may be directed superficially over the patient to the ground, resulting in no injury and minor burns.

  • Electrocardiography is indicated for all patients evaluated for lightning strike. Additional testing should be based on specific signs and symptoms.

  • Lightning strike patients who present without symptoms or signs of injury, or with only minor first-degree burns, and with a normal ECG can be discharged home from the ED after evaluation.

  • Lightning strike can cause fixed, dilated pupils in the absence of irreversible brain injury.

Foundations

Background and Importance

Electrical injuries are uncommon but can cause significant morbidity and mortality. Toddlers and younger children experience low-voltage injuries in the household as the result of contact with electric sockets and cords. Adolescents and young adults more frequently experience high-voltage injury from contact with electric lines outside of houses. Another peak occurs in the third to fourth decade of life, almost exclusively in men with occupational injuries due to high-voltage encounters with power lines and, to a lesser extent, from electric tools. Worldwide, electrical injuries comprise less than 5% of admissions to burn units, but in developing countries this proportion is much higher at 25%. Forensic reports of deaths caused by electrical injury show that the overwhelming majority of victims are men and most deaths are accidental, with a minority attributed to suicide or homicide.

Anatomy, Physiology, and Pathophysiology

Electrical Injury

Current and Voltage

Joule’s law , which describes the amount of thermal energy applied to tissues from electricity, is described by the formula


P = I 2 RT

where P is thermal energy, I the current, R the resistance, and T is the duration (time) that the electricity is applied. Current is the flow of electrons down an electrical gradient and is measured in units of amperage. Current is the most important factor in determining the degree of energy transmitted, but it is rarely known in a given exposure. Instead, voltage is used as a proxy for current. According to Ohm’s law , current (I) is directly proportional to the voltage (V) of the source and inversely proportional to the resistance (R) of the material through which it flows (I = V/R).

Injuries are conventionally classified as being caused by high- or low-voltage sources, with 1000 V as the dividing line. In North America, household sources are low voltage, typically 120 or 240 V. High-voltage injuries, such as those caused by electrical power lines or occupational accidents, are characterized by partial to full-thickness skin burns, deep tissue destruction, and potential cardiac or respiratory arrest. High-voltage injuries are associated with higher rates of death, and more associated traumatic injuries, such as extremity fractures, blunt head injuries, and spinal cord injuries. , Low-voltage exposure causes less surface damage, but may be equally lethal, particularly in cases in which skin resistance is low, such as when immersed or exposed to water.

Current Type

Electrical sources create current that flows in one direction ( direct current, DC ) or alternates direction cyclically at varying frequencies ( alternating current, AC ). The few systems in the United States that use DC include batteries, automobile electronics, and railroad tracks. Exposure to DC most frequently causes a single, strong, muscular contraction. This may throw the victim back from the source in a way that limits duration of exposure but can result in other traumatic injuries. AC is more commonly used (e.g., household currents) because it conveniently allows for an increase or decrease of power at transformers. It is more dangerous than DC of similar voltage because amperage above the so-called “let-go” current will cause muscular tetanic contractions. Because the flexor muscles of the upper extremities are stronger than extensor muscles, these contractions pull the victim closer to the source resulting in prolonged exposure. Box 130.1 shows the physical effects of different amperage levels at a common 60-Hz AC exposure.

BOX 130.1
Physical Effects of Different Amperage Levels a

a At 60-Hz AC exposure.

From Centers for Disease Control. Worker deaths by electrocution: a summary of NIOSH surveillance and investigative findings. www.cdc.gov/niosh/docs/98-131/pdfs/98-131.pdf .

  • 1 mA—barely perceptible

  • 6–9 mA—usual range of let-go current

  • 16 mA—maximum current that an average person can grasp and let go

  • 20 mA—paralysis of respiratory muscles

  • 100 mA—ventricular fibrillation threshold

  • 2 A—cardiac standstill and internal organ damage

Capacitors store electric charge in circuits, and discharge from these devices may result in sudden bursts of very large amounts of electrical energy. Injury from a capacitor may occur even when the electrical device is not energized or plugged in into an electrical source.

Resistance of Tissue Affected

Resistance is the degree to which a substance resists the flow of current; when resistance goes down, current increases. Resistance varies among body tissues. Neurovascular tissues are good conductors of electricity, whereas skin, tendons, fat, and bone are relatively poor conductors ( Box 130.2 ). Current that is initially unable to pass through skin will create thermal energy and cause significant burns. As the skin blisters and deteriorates, its resistance decreases. Once current is through the skin, it can pass easily along lower resistance structures, causing deep tissue injury which may not be immediately evident. As a result, the degree of burns seen on the surface of the skin typically underestimates the damage occurring below the surface. As current strength increases, the relative resistance of tissues ceases to determine the pathway of current, and the entire body functions as a conductor. Current may also jump across skin surfaces in a behavior termed arcing , resulting in prominent burns across flexor surfaces.

BOX 130.2
Resistance of Body Tissues a

a Lowest to highest.

Lowest

  • Nerve

  • Blood vessels

  • Muscle

  • Skin

  • Tendon

  • Fat

  • Bone

Highest

Within a given tissue, resistance differs based on the fluid and electrolyte content of cells. Dry skin offers the largest resistance, up to 100,000 ohm (Ω) in thick, calloused skin, but dermal resistance decreases to as little as 1000 Ω when wet. This explains why electrical injuries are generally worse in the setting of water.

Path Taken by Current Through the Body

The pathway followed by electrical current determines morbidity and mortality. The entrance and exit sites of the electrical current typically demonstrate greater evidence of skin damage, with full-thickness burns commonly encountered. These sites are properly referred to as the source and ground contact points . A patient may have one or multiple source and ground contact points. The most common points of source contact are the hands, wrists, and arms, but children also present with burns from oral contact with electric cords or sockets. The most common ground contact points are the heels of the feet.

Electrical current passing through a limb causes greater local tissue damage than current passing through the trunk because the smaller cross-sectional area limits the ability to dissipate heat. However, current passing through the trunk results in greater mortality due to the involvement of more vital cardiothoracic organs. Transthoracic pathways (arm to arm) are more likely to generate dysrhythmias and have higher mortality rates than vertical currents (leg to arm) or straddle pathways (leg to leg).

Duration of Contact

The degree of tissue damage is directly proportional to the duration of exposure for all voltage levels. Exposure times greater than the length of one cardiac cycle tend to generate dysrhythmias, likely in a manner analogous to the R-on-T phenomenon.

Lightning Injury

Although the same basic scientific principles of electricity apply to lightning, there are several major differences. Lightning strikes involve hundreds of millions of volts, significantly more than those from electrical sources. In contrast, the duration of contact is drastically shorter, averaging 30 microseconds. As a result, current flow is altered, with most of the energy passing over rather than through a victim (termed the “flashover effect”). This reduction in penetration explains why lightning strikes paradoxically result in less destruction to tissues compared with lower-voltage electrical injuries.

Lightning takes various forms, described as streaked, forked, ribbon, sheet, or beaded. The most unusual form is ball lightning, which appears as a globe, rolls along structures, and may even pass through open doors or windows. Strikes occur from cloud to cloud, cloud to ground, and less commonly, ground to cloud.

Lightning may strike a person directly or indirectly. A person’s chances of being struck are increased by wearing or carrying metal objects (such as golf clubs or umbrellas) or other conductors. Current from lightning may reach the body indirectly by traveling through a tree or other object (contact voltage), through the ground or even through the air from a struck object (side flash, or splash injury). Side flashes may travel as far as 30 meters.

The risk of injury from a ground strike is increased when one contact point on the victim (e.g., the right foot) is closer to the strike than a second contact point (e.g., the left foot), thus creating a potential difference. This is referred to as the “stride voltage” and is likely responsible for cattle deaths in a pasture after a thunderstorm. Hence, when out in the open during a storm, risk of a lightning strike can be reduced by placing an insulating material, such as a raincoat, between the ground and the body and assuming the lightning position, a squatting configuration with the feet together, or by curling up in a ball on the ground to reduce the number of contact points. Box 130.3 lists safety tips for avoiding lightning strikes.

BOX 130.3
Tips to Avoid Lightning Strike

  • Seek shelter inside an enclosed building or metal-topped automobile.

  • Avoid large flat, open areas or hilltops.

  • Avoid contact with metal objects and remove metal objects, such as jewelry or hairpins.

  • Avoid trees, boats, and open water.

  • If caught on open ground, curl up on your side with hands and feet close together to reduce contact points, or squat with feet together. If possible, place a rubber raincoat under your body or feet to reduce ground current effects.

  • If in a forest, seek shelter under a thick growth of shorter trees.

  • If indoors, avoid the use of wired phones and contact with plumbing or electrical appliances.

Injury occurs from the force of a strike, blunt trauma when the victim is thrown, the superheating of metallic objects in contact with the patient, barotrauma, or penetrating trauma from shrapnel.

Conducted Energy Weapons

Conducted energy weapons (CEW), commonly known as Tasers or stun guns, are now widely used in law enforcement. These weapons deliver brief bursts of high-voltage, low-amperage direct current. Although CEWs have been associated with several high-profile police-involved fatalities, a clear causal link between their use and a death has not been established.

The most commonly known CEWs are the Taser (Axon Enterprise, Inc.) ( Fig. 130.1 ). These weapons consist of a hand-held unit with two barbs ( Fig. 130.2 ) with connecting cables that are deployed by the user at distances of up to 25 feet. The units typically lodge in the skin or clothing and then automatically deliver a 5-second burst of energy. Further energy bursts can be delivered at the user’s discretion. When these barbs lodge in the person at a distance from one another, they cause an energy arc that results in general muscle contraction and neuromuscular incapacitation (NMI). Newer devices have been developed to create a larger barb spread at close range to maximize the arc distance and more readily induce NMI.

Fig. 130.1, Commonly used conducted energy weapon—Taser X26.

Fig. 130.2, Taser barbs that deliver electrical burst, causing neuromuscular incapacitation.

CEWs may also include a touch-stun mode, in which direct contact of the weapon to the person is required to deliver an electrical energy pulse. In these cases, the barbs are not deployed, and the subject experiences localized pain but will not undergo NMI.

Clinical Features

Electrical Injury

At the cellular level, current causes damage to cell membranes and alters membrane solubility, leading to electrolyte abnormalities and cellular edema. This process, termed electroporation , eventually leads to irreversible cell damage and death. At the tissue and organ levels, electrical current produces damage when electrical energy is converted to thermal energy. Electrical injury rarely causes immediate death, but when it does, it is often due to current-induced cardiac arrest (ventricular fibrillation or asystole), respiratory arrest due to respiratory muscle paralysis, or brainstem injury. Commonly reported delayed complications of electrical injuries include sepsis, acute renal failure, wound infections, and amputations.

Lightning Injury

In contrast to electrical injury, lightning injuries involve very brief exposure to high-voltage energy. General effects are thus quite different than electrical injury, with deep muscle injury being much less common. Instead, lightning more commonly causes blunt traumatic injuries or cardiopulmonary arrest from transient stunning and disruption of the pacemaker cells and brainstem.

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