Which of the following identifies a major mechanism of electricity-induced injury?

AC changes direction frequently; it is the current usually supplied by household electrical outlets in the US and Europe. DC flows in the same direction constantly; it is the current supplied by batteries. Defibrillators and cardioverters usually deliver DC current. How AC affects the body depends largely on frequency. Low-frequency (50- to 60-hertz [Hz]) AC is used in US (60 Hz) and European (50 Hz) households. Because low-frequency AC causes extended muscle contraction (tetany), which may freeze the hand to the current’s source and prolong exposure, it can be more dangerous than high-frequency AC and is 3 to 5 times more dangerous than DC of the same voltage and amperage. DC exposure is likely to cause a single convulsive contraction, which often throws the person away from the current’s source.

For both AC and DC, the higher the voltage (V) and amperage (A), the greater the ensuing electrical injury (for the same duration of exposure). Household current in the US is 110 V (standard electrical outlet) to 220 V (used for large appliances, eg, refrigerator, dryer). High-voltage (> 500 V) currents tend to cause deep burns Burns Burns are injuries of skin or other tissue caused by thermal, radiation, chemical, or electrical contact. Burns are classified by depth (superficial and deep partial-thickness, and full-thickness)... read more

Tissue damage due to electrical exposure is caused primarily by the conversion of electric energy to heat, resulting in thermal injury. Amount of dissipated heat energy equals amperage2 × resistance × time; thus, for any given current and duration, tissue with the highest resistance tends to suffer the most damage. Body resistance (measured in ohms/cm2) is provided primarily by the skin, because all internal tissue (except bone) has negligible resistance. Skin thickness and dryness increase resistance; dry, well-keratinized, intact skin averages 20,000 to 30,000 ohms/cm2. For a thickly calloused palm or sole, resistance may be 2 to 3 million ohms/cm2; in contrast, moist, thin skin has a resistance of about 500 ohms/cm2. Resistance for punctured skin (eg, cut, abrasion, needle puncture) or moist mucous membranes (eg, mouth, rectum, vagina) may be as low as 200 to 300 ohms/cm2.

If skin resistance is high, more electrical energy may be dissipated at the skin, resulting in large skin burns but less internal damage. If skin resistance is low, skin burns are less extensive or absent, and more electrical energy is transmitted to internal structures. Thus, the absence of external burns does not predict the absence of electrical injury, and the severity of external burns does not predict the severity of electrical injury.

Damage to internal tissues depends on their resistance as well as on current density (current per unit area; energy is concentrated when the same current flows through a smaller area). For example, as electrical energy flows in an arm (primarily through lower-resistance tissues, eg, muscle, vessels, nerves), current density increases at joints because a significant proportion of the joint’s cross-sectional area consists of higher-resistance tissues (eg, bone, tendon), which decreases the area of lower-resistance tissue; thus, damage to the lower-resistance tissues tends to be most severe at joints.

Electrical field strength is the intensity of electricity across the area to which it is applied. It, along with Kouwenhoven’s factors Kouwenhoven’s factors Electrical injury is damage caused by generated electrical current passing through the body. Symptoms range from skin burns to damage to internal organs and other soft tissues, cardiac arrhythmias... read more , also determines the degree of tissue injury. For instance, 20,000 volts (20 kV) distributed across the body of a man who is about 2 m (6 ft) tall result in a field strength of about 10 kV/m. Similarly, 110 volts, if applied only to 1 cm (eg, across a young child’s lip), result in a similar field strength of 11 kV/m; this relationship is why such a low-voltage injury can cause the same severity of tissue injury as some high-voltage injuries applied to a larger area. Conversely, when considering voltage rather than electrical field strength, minor or trivial electrical injuries technically could be classified as high voltage. For example, the shock received from shuffling across a carpet in the winter involves thousands of volts but causes inconsequential injury.

The electrical field effect can cause cell membrane damage (electroporation) even when the energy is insufficient to cause any thermal damage.

Application of low electrical field strength causes an immediate, unpleasant feeling (being “shocked”) but seldom results in serious or permanent injury. Application of high electrical field strength causes thermal or electrochemical damage to internal tissues. Damage may include

• Hemolysis

• Protein coagulation

• Coagulation necrosis of muscle and other tissues

• Thrombosis

• Dehydration

• Muscle and tendon avulsion

High electrical field strength injuries may result in massive edema, which, as blood in veins coagulates and muscles swell, can result in compartment syndrome Compartment Syndrome Compartment syndrome is increased tissue pressure within a closed fascial space, resulting in tissue ischemia. The earliest symptom is pain out of proportion to the severity of injury. Diagnosis... read more . Massive edema may also cause hypovolemia and hypotension. Muscle destruction can result in rhabdomyolysis Rhabdomyolysis Rhabdomyolysis is a clinical syndrome involving the breakdown of skeletal muscle tissue. Symptoms and signs include muscle weakness, myalgias, and reddish-brown urine, although this triad is... read more and myoglobinuria, and electrolyte disturbances. Myoglobinuria, hypovolemia, and hypotension increase risk of acute kidney injury Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more . The consequences of organ dysfunction do not always correlate with the amount of tissue destroyed (eg, ventricular fibrillation Ventricular Fibrillation (VF) Ventricular fibrillation causes uncoordinated quivering of the ventricle with no useful contractions. It causes immediate syncope and death within minutes. Treatment is with cardiopulmonary... read more

Symptoms and Signs of Electrical Injuries

Burns Burns Burns are injuries of skin or other tissue caused by thermal, radiation, chemical, or electrical contact. Burns are classified by depth (superficial and deep partial-thickness, and full-thickness)... read more

Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more

Young children who bite or suck on extension cords can burn their mouth and lips. Such burns may cause cosmetic deformities and impair growth of the teeth, mandible, and maxilla. Labial artery hemorrhage, which results when the eschar separates 5 to 10 days after injury, occurs in up to 10% of these young children.

An electrical shock can cause powerful muscle contractions or falls (eg, from a ladder or roof), resulting in dislocations Overview of Dislocations A dislocation is complete separation of the 2 bones that form a joint. Subluxation is partial separation. Often, a dislocated joint remains dislocated until reduced (realigned) by a clinician... read more (electrical shock is one of the few causes of posterior shoulder dislocation Shoulder Dislocations In shoulder (glenohumeral) dislocations, the humeral head separates from the glenoid fossa; displacement is usually anterior. Shoulder dislocations account for about half of major joint dislocations... read more

Overview of Fractures A fracture is a break in a bone. Most fractures result from a single, significant force applied to normal bone. In addition to fractures, musculoskeletal injuries include Joint dislocations... read more

Overview of Fractures A fracture is a break in a bone. Most fractures result from a single, significant force applied to normal bone. In addition to fractures, musculoskeletal injuries include Joint dislocations... read more

The first priority is to break contact between the patient and the current source by shutting off the current (eg, by throwing a circuit breaker or switch, by disconnecting the device from its electrical outlet). High- and low-voltage power lines are not always easily differentiated, particularly outdoors. CAUTION: To avoid shock, rescuers should not try to disengage anyone entangled in power lines (whether of high or low voltage) until the power is shut off.

Patients are resuscitated while being assessed. Shock Prognosis Shock is a state of organ hypoperfusion with resultant cellular dysfunction and death. Mechanisms may involve decreased circulating volume, decreased cardiac output, and vasodilation, sometimes... read more , which may result from trauma or massive burns, is treated. Standard burn fluid resuscitation formulas, which are based on the extent of skin burns, may underestimate the fluid requirement in electrical burns; thus, such formulas are not used. Instead, fluids are titrated to maintain adequate urine output (about 100 mL/h in adults and 1.5 mL/kg/h in children). For myoglobinuria, maintaining adequate urine output is particularly important, while alkalinizing the urine may help decrease the risk of renal failure Acute Kidney Injury (AKI) Acute kidney injury is a rapid decrease in renal function over days to weeks, causing an accumulation of nitrogenous products in the blood (azotemia) with or without reduction in amount of urine... read more . Surgical debridement of large amounts of muscle tissue may also help to decrease myoglobinuric renal failure.

Severe pain due to an electrical burn is treated by the judicious titration of IV opioids.

Asymptomatic patients who are not pregnant, have no known heart disorders, and who have had only brief exposure to household current usually have no significant acute internal or external injuries that would necessitate admission and can be discharged.

Cardiac monitoring for 6 to 12 hours is indicated for patients with the following conditions:

• Any suggestion of cardiac damage

• Known heart disorders (possibly)

All patients with significant electrical burns should be referred to a specialized burn unit. Young children with lip burns should be referred to a pediatric orthodontist or oral surgeon familiar with such injuries.