A strike of lightning is one of the most common environmental causes of sudden cardiac death and is responsible for between 50 and 300 deaths annually in the United States.^1,² Cloud-to-ground lighting strikes, the most destructive form of lightning, occur approximately 30 million times each year,³ most often in Florida and along the southeastern coast of the Gulf of Mexico.⁴ Lightning has struck more than 10 miles away from the rain of a thunderstorm, so the danger may not always be obvious or apparent.³ Electrical injuries can be equally devastating. The spectrum of injuries from both can range dramatically from minor, localized injuries to death.

Although lightning injury may be one of the most common injuries caused by natural phenomena, its incidence has not been tracked accurately. The incidence is higher in males and in people between 20 and 44 years of age, three of every four occurred in the South or Midwest, and one in four was work related.⁵ Sport-, wilderness-, and travel-related activities also place people at higher risk for lightning injuries.

Electrical injuries tend to occur in patients in three distinct age groups. The first group is toddlers who encounter household electrical sockets, cords, and appliances. The second is adolescents who engage in risky behavior. The third group comprises adults who work with electricity. Electrical burns account for between 3% and 7% of admissions to burn centers in the United States each year, many of which are occupational injuries. The annual occupational death rate from electrocution is 1 per 100,000; this type of death occurs more frequently in utility workers, miners, and construction workers.⁶

Pathophysiology

Definitions that should be familiar to those caring for patients with electrical injuries are listed in Box 132.1. Electrical current is the movement of electrical charge from one location to another. Current strength is expressed in amperes. Materials that allow electrical current to flow easily (low resistance) are referred to as conductors. Materials that do not allow flow of electrical current are called insulators.

Box 132.1 Definitions of Electrical Injuries

Alternating current (AC): Electrical source with changing direction of current flow

Current: Flow of electrons per second (measured in amperes)

Direct current (DC): Electrical source with unchanging direction of current flow

Frequency: Number of transitions from positive to negative per second in AC

Resistance: Tendency of a material to resist the flow of electrical current (measured in ohms)

Volt: Unit of electrical force

All body tissues conduct electricity to some extent. Tissues with high fluid content conduct better than those with lower fluid content. Nerves tend to offer the least resistance, whereas bones offer the most. Table 132.1 lists body tissues according to level of resistance. Skin resistance can vary substantially, with wet skin having the lowest resistance. Factors determining the severity of the injury caused by the electrical current are listed in Box 132.2.

Table 132.1 Level of Resistance of Body Tissues to Electricity

LEVEL OF RESISTANCE	TISSUE
Low	Nerves Blood vessels Mucous membranes Muscle

Intermediate

High

Box 132.2

Factors Determining the Severity of Electrical Injury

Type of circuit

Whether the current was alternating or direct

Duration of contact

Voltage (electrical potential)

Resistance of tissues

Amperage (current intensity)

Environmental circumstances

Pathway of the current

From Arrowsmith J, Usgaocar RP, Dickson WA. Electrical injury and the frequency of cardiac complications. Burns 1997;23:576-8.

Any electrical charge greater than 1000 V is generally considered high voltage, although some authorities have argued that the risk for significant injury increases with charges exceeding 600 V. Typical household circuits in the United States are 110 V, with bigger appliances operating on 220-V circuits. Power lines in residential areas can have more than 7000 V.

Electricity causes injury in several ways, as listed in Box 132.3. As current passes through the body, the tissues through which it passes are heated, and significant damage can occur. The emergency physician (EP) must be aware of the potential for internal damage when caring for a victim of electrical injury; not all patients with significant internal injuries display significant external damage. Arc burns result from an electrical source through the air and can cause significant damage. Temperatures can reach 2500° C, which can ignite clothes or nearby material and cause thermal injuries. Flash burns occur when current strikes the body but does not penetrate the skin.

Box 132.3 Mechanisms of Electrical Injury

Direct tissue damage (entry and exit sites)

Internal thermal heating

Induced muscle contraction

Flash burns

Arc burns

Blunt trauma

Lightning delivers high-voltage direct current that tends to flow over the body rather than enter it. This event, often referred to as flashover, is one explanation for how people are able to sometimes survive exposure to such high voltage. Lightning current can also enter the victim and cause significant damage, particularly to the cardiac, respiratory, and neurologic systems. Blunt injury has been reported in up to one third of lightning victims ⁷ as a result of both the direct force of the strike and rapid expansion of the surrounding air, which often causes the victim to fall or be struck by flying debris. Lightning can also cause thermal injury (burns) by hot steam produced from surrounding moisture or by metal objects heated by the electricity. Box 132.4 lists the mechanisms of injury from lightning strikes.

Box 132.4 Mechanisms of Injury from Lightning Strikes

Direct strike

Contact strike: Lightning strikes an object that the victim is touching

Side flash: Lightning strikes a nearby object, and electrical current then traverses the air to strike the victim (can involve multiple victims)