Etiology

Electrical injuries can occur at home, in the workplace, or outdoors as a result of lightning. Electrical injuries are arbitrarily divided into high voltage of 1000 V or more and low voltage of less than 1000 V.

Home electricity is usually alternating current (AC). In the US, Canada, and the Caribbean, home voltage is typically 110 V at 60 Hz, with 220 V used for high-power appliances. In Europe and Australia, household voltage is typically 220 V to 240 V at 50 Hz.

Direct current (DC) is a constant current and commonly used in industrial settings. In industry, higher voltage sources are common. As a consequence, workers may be exposed to voltages hundreds of times higher than found in the typical home.

Lightning is present in all thunderstorms. The National Weather Service (US) estimates that 100,000 thunderstorms occur in the US each year. Cloud-to-ground lightning occurs approximately 30 million times each year. Lightning can produce 10 million volts or more of DC, although exposure time is generally brief.

The use of electronic control devices has increased worldwide in recent years. These devices deliver a temporary high-voltage, low-current electrical discharge to override natural muscle-triggering mechanisms. A single exposure of an electronic control device on healthy individuals can be assumed to be generally safe, but can have deleterious effects when used in the field, in particular if persons receive multiple exposures, are intoxicated, show signs of "excited delirium", or present with medical comorbidities.[14]

There are anecdotal reports of people being electrocuted by smartphones, but there do not appear to be any substantiated claims. Smartphones work on 5 volts, so electrocution is unlikely. Nevertheless, the charging cable that is plugged into the wall presents the same dangers as any electrical home appliance. Reports of burns caused by e-cigarettes appear to be related to overheating of batteries, rather than an electrical injury.[15]

Pathophysiology

The physical laws governing electricity are important for an understanding of the pathophysiology of electrical injuries.

Transfer of electrical energy into the body is a complex phenomenon that is extremely variable and situation-dependent, but will follow certain natural laws. Accidental exposure to electricity can produce no injuries or be instantly fatal.

Electricity flows in circuits that contain voltage, current, and resistance. For practical purposes, there must be a complete circuit for electricity to flow. The circuit may be completed back to the electrical source itself or by contact with a ground, a phenomenon called "earthing". Any surface that has a lower electrical potential than the source voltage will act as a ground and complete the circuit.

Ohm's law states that current, voltage, and resistance exist in a proportional relationship, V = IR (V = voltage, I = current, R = resistance). The tissues of the body are in effect the resistance that determines the current that will flow through the body. Higher resistance leads to lower current flow; for a current to pass through the body, the resistance in the human body needs to be less than the surroundings. Tissue resistance will vary, with dry thick skin presenting the greatest resistance and moist broken skin or mucous membranes representing the least. For example, a dry finger would have 40,000-1,000,000 ohms of resistance, whereas a wet finger would have a lower resistance of 4000. The voltage drop across this resistance will generate heat, so high-resistance tissues will be more likely to suffer a thermal burn whereas areas of lower resistance, such as nerves and blood vessels, would allow flow through the body affecting internal organs, especially the heart.

Electricity adversely affects the cardiac conduction system, causing arrhythmias, and can cause direct myocardial damage. High voltage or DC current usually causes asystole, and AC current usually causes ventricular fibrillation (VF).

If, for example, a worker comes into contact with a voltage source and completes a circuit through both hands, current will flow through the heart. This situation is potentially more dangerous and arrhythmogenic than if the circuit completes through the right hand and foot, where the heart will be spared.

The respiratory drive may arrest due to paralysis or tetanic contractions of the respiratory muscles. Skin and deep burns, neurologic sequelae, and electrical vascular injury are also common.[16]

Lightning delivers a very high voltage direct current of short duration. Thus, the actual amount of energy may be less than with other exposure. As a consequence, victims of lightning exposure rarely sustain extensive tissue destruction or large cutaneous burns, but have significant damage to the conduction system of the heart.

DC causes a single muscle contraction, whereas AC causes tetanic muscle contraction. AC shock of the hands may cause tetanic contractions that prevent the person from letting go, increasing the energy delivered to the body.

Classification

Types of electrical injury[1]

1. Electrocution (fatal)

2. Electric shock

3. Burns

4. Electronic control devices (e.g., Taser)

5. Falls caused by contact with electric energy.

Mechanism of electrical injury[1]

1. Electric shock

  • Direct contact with electrical energy

2. Electric arc burn

  • Flow of electrons through a gas (such as air) to a victim at ground potential (supplying an alternative path to air).

  • Heat generated by an electrical arc can also cause flash burns.

3. Electric contact burn injury

  • May be internal or external.

  • Thermal injuries (flash or flame burns) - current does not flow through the body and injuries are usually confined to the skin.

  • High-voltage burns may have significant underlying injury with inconspicuous entry and exit wounds.

Types of electrical injury[2]

1. Low voltage

  • Less than 1000 volts

  • Usually occurs in the home

2. High voltage

  • Greater than 1000 volts

  • Usually occurs at work

Typical injuries[2]

1. Skin

Note: all types of electrical injury may result in partial- to full-thickness wounds, and can affect subcutaneous tissues.

  • Electrothermal burns - entrance and exit wounds

  • Arc burn

  • Flame burns

  • Lightning injuries - Lichtenberg figures (fern-like pattern on skin) are pathognomonic

2. Respiratory

  • Respiratory arrest as a consequence of central nervous system inhibition, prolonged paralysis of respiratory muscles, tetanic contraction of respiratory muscles, or as part of cardiorespiratory arrest

3. Cardiovascular

  • Arrhythmias - VF common in low-voltage AC current shock; asystole common in high-voltage shock (AC or DC)

  • Conduction abnormality - sinus bradycardia and high-degree AV block

  • Myocardial damage - direct injury or ischemia from coronary artery spasm or hypotension

4. Musculoskeletal

  • Bone - severe electrothermal injuries (e.g., periosteal burns, destruction of bone matrix, osteonecrosis); fractures and dislocation due to falls and forceful tetany

  • Muscle - edema and tissue necrosis resulting in compartment syndrome and rhabdomyolysis

5. Neurologic

  • Common manifestations - loss of consciousness, generalized weakness, autonomic dysfunction, respiratory depression and memory problems

  • Keraunoparalysis (lightning paralysis) - reversible, transient paralysis; associated sensory disturbances and peripheral vasoconstriction

  • Hypoxic encephalopathy, intracerebral hemorrhage, and cerebral infarction

  • Sensorineural hearing loss and hypoacusis due to ruptured eardrums

Use of this content is subject to our disclaimer