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Electrical Injuries

Author: Tracy A Cushing, MD, MPH, Instructor in Medicine, Department of Emergency Medicine, Harvard Medical School; Attending Physician, Department of Emergency Medicine, Mount Auburn Hospital
Coauthor(s): Ronald K Wright, MD, JD, Associate Professor (Retired), Department of Pathology, University of Miami School of Medicine; Private Practice, Forensic Pathology
Contributor Information and Disclosures

Updated: Oct 7, 2009

Introduction

Background

Electrical injuries, although relatively uncommon, are inevitably encountered by most emergency physicians. Adult electrical injuries usually occur in an occupational setting, whereas children are primarily injured in the household setting. The spectrum of electrical injury is very broad, from minimal injury to severe multiorgan involvement, with both occult and delayed complications, to death.

Pathophysiology

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

Electrical injuries are typically divided into high-voltage and low-voltage injuries, using 500V or 1000V as the cutoff. High morbidity and mortality has been described in 600V direct current injury associated with "third rail" contact.² In the United States and Canada, typical household electricity provides 110V for general use and 240V for high-powered appliances, while industrial electrical and high-tension power lines can have more than 100,000V.³ Voltage is directly proportional to current and indirectly proportional to resistance, as expressed by Ohm's Law: 

V = I X R; where I = current, V = voltage, R = resistance.
 
Current

The volume of electrons flowing across the potential gradient is the current, which is measured in amperes (I). 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–the maximum current at which a person can grasp the current and then release it before muscle tetany makes letting go impossible. The "let go" current for the average child is 3-5 mA; this is well below the 15-30 A of common household circuit breakers. For adults, the "let go" current is 6-9 mA, slightly higher for men than for women. Skeletal muscle tetany occurs at 16-20 mA. Ventricular fibrillation can occur at currents of 50-100 mA.⁴  
 
Resistance

The impedance to flow of electrons across the gradient is the resistance (R) and varies depending on 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.⁵ Heavily calloused areas of skin are excellent resistors, whereas a moderate amount of water or sweat on the skin surface can decrease its resistance significantly.
 
Type of circuit

Electrical current can flow in 1 of 2 types of circuits: direct current (DC) or alternating current (AC), in which the flow of electrons changes direction in rhythmic fashion. AC is the most common type of electricity in homes and offices, standardized to a frequency of 60 cycles/sec (Hz).
 
High-voltage DC often causes a large single muscle contraction that throws the victim away from the source; thus, usually only brief duration of contact occurs with the source flow. In contrast, AC of the same voltage is considered to be approximately 3 times more dangerous than DC, because the cyclic flow of electrons causes muscle tetany that tends to prolong victims' exposure to the source. Muscle tetany occurs when fibers are stimulated at 40-110 Hz; thus, the standard 60 Hz of household current is within that range. If the source contact point is the hand, when tetanic muscle contraction occurs the extremity flexors contract, causing the victim to grasp the current and bring it closer to the body causing prolonged contact with the source. 

Table 1.  Physiologic Effects of Different Electrical Currents 

 

Open table in new window

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 as well as deeper tissues, depending on their resistance. It will typically cause damage at the source contact point and the ground contact point.

• Electrical arcs: Current sparks are formed between objects of different electric potential 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 2500-5000^o C, 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 direct current 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 surface area of the body but are usually only partial thickness.

Frequency

Electrical injuries are estimated to cause approximately 500-1000 deaths per year in the United States.^3,4 They are responsible for 3-5% of all burn unit admissions and cause 2-3% of emergency department burn visits in the pediatric population. Some evidence exists that the incidence of low-voltage injuries among children is declining, perhaps because of widespread use of ground fault circuit interrupters (GFCIs), but rates of high-voltage injuries, usually involving power lines or rail sources, has remained steady.⁶ Due to the nature of occupational hazards with electricity, electrical injuries represent the fourth leading cause of work-related traumatic death (5-6% of all workers deaths).⁷

United States

More than 500 lightning deaths and generated electrical deaths per year are estimated to occur. Between 3 and 5% of burn unit admissions are associated with electrical burns.

Mortality/Morbidity

Morbidity and mortality are largely affected by the particular type of electrical contact involved in each exposure. Overall mortality is estimated to be 3-15%.^1,8 Flash burns have a better prognosis than arc or conductive burns.⁵  
 
Persons who experience low-voltage injuries without immediate cardiac or respiratory arrest have low mortality, but they may have significant morbidity from oral trauma in children who bite electrical cords⁹ or adults who suffer burns to the hand.
 
Persons who experience low-voltage injuries with cardiac or respiratory arrest may recover completely with immediate CPR on scene; however, prolonged CPR and transport may result in permanent brain damage.
 
High-voltage injuries often produce severe burns and blunt trauma. Patients are at high risk of myoglobinuria and renal failure. Burns are often ultimately much worse than they initially appear in the ED.

Race

No racial susceptibility to electrical burns exists. Occupational trends show more Caucasian tradespeople in high-risk occupations, and therefore Caucasians are more likely than other races in the United States to experience occupation-related electrical injuries.

Sex

Rates of childhood electrical injury are higher among boys than girls⁶ ; rates of adult injury are significantly higher in men than in women, likely because of occupational predisposition. Most series show more than 80% of electrical injuries occurring in men.^8,10,11,12

Age

A bimodal distribution of electrical injuries exists among the very young (children <6 y) and again among young adults/working age.¹³ Patterns of electrical injury vary by age (eg, low voltage household exposures among toddlers and high-voltage exposures among risk-taking adolescents and via occupational exposure). Mechanisms of pediatric injury have been reviewed.^14,13

Clinical

History

• Low-voltage AC injury without loss of consciousness and/or arrest: These injuries are <1000V exposures usually in the home or office setting. Typically, children with electrical injuries present after biting or chewing on an electrical cord and suffer oral burns. Adults working on home appliances or electrical circuits can also experience these electrical injuries. Low-voltage AC may result in significant injury if there is prolonged, tetanic muscle contraction. 
• Low-voltage AC injury with loss of consciousness and/or arrest: In respiratory arrest or ventricular fibrillation that is not witnessed, an electrical exposure may be difficult to diagnose. All unwitnessed arrests should include this possibility in the differential diagnosis. Query EMS personnel, family, and coworkers about this possibility. Inquire if a scream was heard before the patient’s collapse; this may be due to involuntary contraction of chest wall muscles from electrical current. 
• High-voltage AC injury without loss of consciousness and/or arrest: Usually high-voltage injuries do not cause loss of consciousness but instead cause devastating thermal burns. In occupational exposures, details of voltage can be obtained from the local power company. 
• High-voltage AC injury with loss of consciousness and/or arrest: This is an unusual presentation of high-voltage AC injuries, which do not often cause loss of consciousness. History may need to come from bystanders or EMS personnel. 
• Direct current (DC) injury: These injuries typically cause a single muscle contraction that throws the victim away from the source. They are rarely associated with loss of consciousness unless there is severe head trauma, and victims can often provide their own history. 

Physical

Electrical injuries can cause multiorgan dysfunction and a variety of burns and traumatic injuries. A thorough physical examination is required to assess the full extent of injuries. Occupational injuries have a high likelihood of future litigation, and physical examination findings should be documented with photographs if possible, with the proper releases, and filed in the patient's medical record.
 
Overall, low-voltage exposure tends to cause less overall morbidity than high-voltage, but it is important to ensure by accurate history that a seemingly low-voltage burn was not in fact from a high-voltage source (like a microwave, computer, or TV monitor — any device that "steps-up" voltage via a transformer). Low-voltage burns can still cause cardiac arrhythmia, seizure, and long-term complications if contact is near the chest or head.

• Cardiovascular: Patients may present in asystole or ventricular fibrillation (VF) in addition to other arrhythmias. Sudden death due to VF is more common with low-voltage AC, whereas asystole is more often associated with high-voltage AC or DC. Ventricular fibrillation can be caused at voltages as low as 50-120 mA, which is lower than the typical household current. One series showed cardiac arrhythmias following 41% of low-voltage injuries.¹² Electricity can also cause conduction abnormalities and direct trauma to cardiac muscle fibers. Survivors of electrical shock can experience subsequent arrhythmia, usually sinus tachycardia and premature ventricular contractions (PVCs). One study identified 3 cases of delayed ventricular arrhythmias up to 12 hours after the incident.¹⁵ Long-term cardiac complications occurring from electrical injury are rare. 
• Respiratory: Chest wall muscle paralysis from tetanic contraction may cause respiratory arrest if the current pathway is over the thorax. Injury to the respiratory control center of the brain can also cause respiratory arrest. The lungs are a poor conductor of electricity and generally are not as susceptible to direct injury from current as tissues with lower resistance. 
• Skin: A variety of burns and thermal injuries occurs from electricity that affect the skin and soft tissues. These are often the most severe sequelae of electrical burns after cardiac arrhythmias, which may initially appear minor despite significant deep tissue injury subsequently requiring fasciotomy or amputation. Burns are often most severe at the source and ground contact points; the source is usually the hands or the head while the ground is often in the feet. The strength and duration of contact with the source largely influence severity and extent of tissue damage. All burns should be carefully documented and, if possible, photographed. 
  • High-voltage electrothermal burns: Typically, these show a contact point and ground point: where the person touched the circuit and where he or she was grounded. These may produce significant damage to underlying tissue while largely sparing the surface of the skin. These burns may appear as painless, depressed areas with central necrosis and minimal bleeding. The presence of surface burns does not accurately predict the extent of possible internal injuries, as skin with high resistance will transmit energy to deeper tissues with lower resistance.

• Arc burns: When an arc of current passes from an object of high to low resistance, it creates a high temperature pathway that causes skin lesions at the site of contact with the source and at the ground contact point (not always the feet). These areas typically have a dry parchment center and a rim of congestion around them. There will be clues to the internal pathway taken by the arc based on the location of these surface wounds. Arcs can also cause electrothermal, flash, and flame burns, so multiple burns of varying appearance may be observed. Arcs do not occur in low-voltage injuries.

• Flash burns: Flash burns are caused by heat from a nearby electrical arc that can reach upwards of 5000^o C. These can pass over the surface of the body or through, depending on the path of the arc causing the flash. They may "splash" over the surface of the body, resulting in diffuse but relatively superficial partial-thickness burns. There is no internal electrical component.

• Flame burns: Flame burns are caused by ignition of clothing or nearby objects. These cause thermal burns similar to other flame burns. 
• Low-voltage burns: These behave like ordinary thermal burns and range from local erythema to full-thickness burns. These require several seconds of contact to cause skin burns, sometimes reaching current levels high enough to cause VF before causing any significant skin damage.⁴ Direct contact burns may occur only if the circuit through the person was prolonged for more than a few seconds.

• Contact burns: Contact burns usually have a pattern from the contacted item (branding) and may appear similar to flash burns. To differentiate them, full-thickness contact burns have unburned surface hair, whereas flash burns singe the hairs, which are largely gone by the time the patient presents to the ED.

• Pediatric oral burns: These are most commonly encountered in children younger than 6 years who bite or suck on a household electrical cord. A local arc of current crosses from one side of the mouth to the other. The orbicularis oris muscle may be involved, and cosmetic deformity of the lips may occur if the burn crosses the commissure. Significant edema may be noted and within 2-3 days eschar formation. Life-threatening bleeding can occur at 2-3 weeks post injury if the labial artery is exposed when the eschar falls off. Initial presentations may underestimate the extent of the ultimate injury; patients require aggressive airway management.⁹ These patients should be referred for early follow-up to a burn specialist, plastic surgeon, and an oral surgeon.
• Neurologic
  • Most acute CNS or spinal deficits resulting from electrical injuries are due to secondary blunt trauma or burns. Often, the patient has transient confusion, amnesia, and impaired recall of events if not frank loss of consciousness. Direct effects of electrical current are most severe if the respiratory control center of the brainstem is affected resulting in respiratory arrest. Current may also cause seizure or direct spinal cord injury if there is hand-to-hand flow. Spinal cord injury can result from direct current effects or blunt trauma. Unless a patient is completely lucid with full recollection of the events, initial C-spine immobilization is indicated.
  • Currents cause acute muscle tetany at relatively low currents and frequencies, like those found in most households. Muscle tetany causes victims to grasp the source, prolonging contact time, and can also paralyze respiratory muscles resulting in asphyxiation.
  • Long-term neurologic complications include seizures, peripheral nerve damage, delayed spinal cord syndromes, and psychiatric problems from depression to aggressive behavior.
• Musculoskeletal: Acute injuries include fracture from blunt trauma and compartment syndrome from burns. The chest and any extremity should be examined for circumferential burn. Palpate the extremity and perform distal neurologic, vascular, and motor examination to determine if there is suspicion of a compartment syndrome. If this is the case, compartment pressure can be measured and early fasciotomy may help prevent subsequent amputation.¹¹ If available, surgical consultation should be obtained early for a patient with these concerns or for appropriate trauma consultation. Massive muscle damage can cause severe rhabdomyolysis and subsequent renal failure.
• ENT/head: The head is a common point of entry for high-voltage injuries. Patients may have perforated tympanic membranes, facial burn, and cervical spine injury. Approximately 6% of victims develop cataracts, usually months after the initial injury, with increasing frequency the closer contact is to the head.^16,10

Causes

Electrical injury occurs when a person becomes part of an electrical circuit or is affected by the thermal effects of a nearby electrical arc. Injuries are caused by high-voltage AC, low-voltage AC, or DC. 

• High-voltage AC: High-voltage 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 by 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, crane), any person touching the conductor can be injured. Occupational injuries may include direct contact with electrical switching equipment and energized components. 
• Low-voltage AC: Generally, 2 types of low-voltage injury occur: children biting into electrical cords producing severe lip, face, and tongue injuries, or the adult who becomes grounded while touching an appliance or other object that is energized. The latter type of injury is decreasing 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 0.005 amps (0.6 W at 120 V). 
• Direct current (DC): DC injuries are generally 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.²

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