Electrical Injuries in Emergency Medicine

Electricity is generated by the flow of electrons across a potential gradient from high to low concentration through a conductive material. The voltage represents the magnitude of this potential difference and is usually determined by the electrical source. The type and extent of an electrical injury is determined by voltage, current strength, resistance to flow, the duration of contact with the source, the pathway of flow, and the type of current (ie, DC or AC).

Voltage

Electrical injuries are typically divided into high-voltage and low-voltage injuries, with 500 V or 1000 V used as the dividing point. High morbidity and mortality have been described in 600 V DC injury associated with railroad "third rail" contact. ^[3] In the United States and Canada, typical household electricity provides 110 V for general use and 240 V for high-powered appliances, whereas industrial electrical and high-tension power lines can carry more than 100,000 V. ^[4] Voltage is directly proportional to current and indirectly proportional to resistance, as expressed by Ohm's law:

• V = I × R

where I = current, V = voltage, and R = resistance.

Current

Current (I) is the volume of electrons flowing across the potential gradient, as expressed in amperes (A). It is a measure of the amount of energy that flows through a body. Energy is perceptible to the touch at a current as low as 1 mA. A narrow range exists between perceptible current and the "let go" current—that is, the maximum current at which a person can grasp and then release the current before muscle tetany makes it impossible to let go.

For children, on average, the "let go" current is in the range of 3-5 mA; this is well below the 15-30 A of common household circuit breakers. For adults, the "let go" current is in the range of 6-9 mA and is slightly higher for men than for women.

Different electrical currents have varying physiologic effects (see Table 1 below). For instance, skeletal muscle tetany occurs at 16-20 mA, and ventricular fibrillation (VF) can occur at currents of 50-120 mA. ^[5]

Table 1. Physiologic Effects of Different Electrical Currents (Open Table in a new window)

Resistance

Resistance (R) is the impedance to flow of electrons across a gradient, as expressed in ohms (Ω). It varies according to the electrolyte and water content of the body tissue through which electricity is being conducted. Blood vessels, muscles, and nerves have high electrolyte and water content (and thus low resistance) and are good conductors of electricity—better than bone, fat, and skin. ^[1] Heavily callused areas of skin are excellent resistors, whereas a moderate amount of water or sweat on the skin surface can decrease its resistance significantly.

Types of circuit

Electrical current can flow in one of two types of circuits: (1) DC, in which electrons flow is unidirectional, and (2) AC, in which the flow of electrons changes direction at a regular frequency. AC is the most common type of electricity in homes and offices and is standardized to a frequency of 50 or (in the United States) 60 cycles/sec (Hz).

High-voltage DC often causes a large single muscle contraction that throws the victim away from the source, resulting in only brief contact with the source flow. In contrast, high-voltage AC is considered to be approximately three times more dangerous than DC of the same voltage because the cyclic flow of electrons causes muscle tetany that prolongs exposure to the source flow. Muscle tetany occurs when fibers are stimulated at 40-110 Hz; the standard 60 Hz of US household current is within that range. When the source contact point is the hand, tetanic muscle contraction induces the extremity flexors to contract, causing the victim to grasp the current source and thereby resulting in prolonged contact with the source.

Types of electrical burns

Depending on the voltage, current, pathway, duration of contact, and type of circuit, electrical burns can cause a variety of injuries through several different mechanisms.

Direct contact

Current passing directly through the body will heat the tissue, causing electrothermal burns both to the surface of the skin and to deeper tissues, depending on their resistance. It will typically cause damage both at the source contact point and at the ground contact point. (See the image below.)

Electrical arcs

Current sparks are formed between objects with differing electric potentials that are not in direct contact with each other, most often a highly charged source and a ground. The temperature of an electrical arc can reach 2500-5000ºC, resulting in deep thermal burns where it contacts the skin. These are high-voltage injuries that may cause both thermal and flame burns in addition to injury from DC along the arc pathway.

Flame

Ignition of clothing causes direct burns from flames. Both electrothermal and arcing currents can ignite clothing.

Flash

When heat from a nearby electrical arc causes thermal burns but current does not actually enter the body, the result is a flash burn. Flash burns may cover a large amount of the body surface area (BSA) but usually are only partial-thickness injuries.

High-voltage alternating current

High-voltage AC injuries most commonly occur from a conductive object touching an overhead high-voltage power line. In the United States, most electric power is distributed and transmitted via bare aluminum or copper conductors, which are insulated by air. If the air is breached by a conductor, (eg, an aluminum pole, antenna, sailboat mast, or crane), any person touching the conductor can be injured. Occupational injuries may include direct contact with electrical switching equipment and energized components.

Low-voltage alternating current

Patients with low-voltage AC injuries generally fall into one of the following two broad categories:

• Children who bite into electrical cords and sustain lip, face, and tongue injuries
• Adults who become grounded while touching an appliance or other object that is energized

Injuries in the second category are becoming less common with the increasing use of ground fault circuit interrupters (GFCIs) in circuits where people might easily become grounded. GFCIs stop current flow in the event of a leakage current (ground fault) if the ground fault is greater than 5 mA (0.6 W at 120 V).

Direct current

DC injuries are commonly encountered when the third energized rail of an electrical train system is contacted while the person is grounded. This sets up a circuit of electric current through the victim, causing severe electrothermal burns and myonecrosis. ^[3]

US statistics

It has been estimated that electrical injuries are estimated to cause as many as 1000 deaths per year in the United States, with a mortality of 3-5%. ^{[4, 5]}  According to data on workplace injuries and fatalities from the US Bureau of Labor Statistics (BLS) and the Occupational Safety and Health Administration (OSHA), electrical fatalities account for 5.6% of all workplace fatalities, and the overall average electrical fatality rate for all occupations is 0.10 per 100,000 workers, with electrical power line installers and repairers at highest risk (6.56 fatalities per 100,000 workers). ^[2]

Electrical injuries have been reported to be responsible for 3-5% of all burn unit admissions and to cause 2-3% of emergency department (ED) burn visits in the pediatric population.

Although there is some evidence that the incidence of low-voltage injuries among children has been declining (possibly because of more widespread use of GFCIs), the incidence of high-voltage injuries, usually involving power lines or rail sources, has not changed significantly. ^[6]  With the near-ubiquity of potental electrical hazards in occupational settings, electrical injuries have come to represent the fourth leading cause of work-related traumatic death (5-6% of all workers' deaths). ^{[2, 7]}

Age-, sex-, and race-related demographics

A bimodal age distribution of electrical injuries exists, with peaks in very young children (< 6 y) and in young and working-aged adults. Patterns of electrical injury vary by age (eg, low-voltage household exposures being more common among toddlers and high-voltage exposures being more common among risk-taking adolescents and via occupational exposure). ^{[8, 9]}

Rates of childhood electrical injury are higher among boys than girls ^{[10, 6]} ; rates of adult injury are significantly higher in men than in women, likely because of occupational predisposition. In most series, more than 80% of electrical injuries have been found to occur in men. ^{[11, 12, 13, 8]}

No racial susceptibility to electrical burns exists. Occupational trends indicate that tradespeople in high-risk occupations are disproportionately White; therefore, this group may be more likely than other racial groups in the United States to experience occupation-related electrical injuries.

For those without prolonged unconsciousness or cardiac arrest, the prognosis for recovery is excellent. Burns and traumatic injuries continue to cause most of the morbidity and mortality from electrical injuries.

Morbidity and mortality are largely affected by the particular type of electrical contact involved in each exposure. Overall mortality is estimated to be 3-5%. ^[11] Flash burns have a better prognosis than arc or conductive burns do. ^[1]

Mortality is generally low in persons who experience low-voltage injuries without immediate cardiac or respiratory arrest, but there may be significant morbidity from oral trauma in children who bite electrical cords ^[14] or adults who suffer burns to the hand.

Persons who experience low-voltage injuries with cardiac or respiratory arrest may recover completely with immediate cardiopulmonary resuscitation (CPR) on scene; however, prolonged CPR and transport time may result in permanent brain damage.

High-voltage injuries often produce severe burns and blunt trauma. Patients are at high risk for myoglobinuria and renal failure. Often, burns ultimately prove to be much worse than they initially appeared in the ED.

One study (N = 118; age range, 4-82 y) of the outcomes of electrical injuries in the ED found that at 2-year follow-up, 43.9% of the patients had aesthetic sequelae and 25.3% had psychological disorders; 7% of adults had been unable to return to their previous occupations. ^[15]