Electrical injury

Overview
Injuries from artificial electricity have been reported for almost three centuries. The exact pathophysiology of electrical injury is not well understood because of the large number of variables that cannot be measured or controlled when an electrical current passes through tissue.

Pathophysiology & Etiology

 * Injuries occur by 3 mechanisms:
 * Direct effect of electrical current on body tissues
 * Conversion of electrical energy to thermal energy
 * Blunt injury from muscle contraction or as a complication of subsequent fall after electrocution.


 * The primary determinant of injury is the amount of current flowing through the body.
 * Voltage
 * Resistance
 * Amperage
 * Type of current
 * Current pathway
 * Duration of contact all influence the extent of injury.


 * Voltage is the electrical pressure that causes current to flow. High voltage is defined as >1000V. High voltage tension lines are >100000V, distribution lines 7-8000V, and homes carry 110V (US) or 220V (Europe). In a lightning strike, the voltage commonly is >100,000,000V.


 * Current is the flow of electrons/sec. Alternating current (AC) accounts for the majority of injures by electricity, while lightning is direct current (DC).  DC causes a single muscle contraction and throws the victim from the site.  AC causes repetitive contractions, increasing duration of contact.  While lightning has a peak DC of 20K-40K Amps, the body is in contact for 1-2 microseconds.  By contrast, AC carries 8-22 mA typically but can result in respiratory muscle paralysis and ventricular fibrillation.


 * Resistance depends on the area of contact, pressure applied, the magnitude and duration of current flow and the presence of moisture. Wet skin has a resistance of 2500 ohms, while dry skin has approximately 100,000 ohms.  The result is that current travels on the wet skin surface and discharges to the ground (“flashover’), while dry skin will cause the current to pass slower and through the body, leading to more injury.


 * A vertical pathway leads to a higher incidence of respiratory arrest and VF as well as CNS complications as compared to the pathways traveling hand-to-hand or below the symphysis pubis.


 * The longer the duration of contact, the lager the amount of thermal energy that is generated. (E=I2RT)

Burns
Burns can range from the superficial, limited variety to the extensive and deep. In many cases, the superficial burns may be unimpressive in comparison to extensive necrosis in deeper tissues. Most of the damage is concentrated to the extremities. Because bone retains heat longer, a central core of necrotic muscle with relative sparing of superficial muscle can be seen.

Blunt Trauma and compartment syndrome
Electrical injury leading to visceral injury and/or rhabdomyolysis can be seen. This results from either muscle contraction, a complication of the subsequent fall or from the shock wave of a lightning bolt. Because the temperature rises within milliseconds to 30,000K (5x hotter than the sun), a shock wave is generated that can be as much as 20 atmospheres due to heating of air. Bones can fracture from falls or under the stress of repetitive tetanic contractions.

Vascular Injury
Vascular injury can occur from compartment syndrome or coagulation of small vessels. It is more often seen in electrical injury rather than lightning. Delayed thrombosis, aneurysm formation and rupture have been noted due to medial coagulation and necrosis.

Cardiac Injury
Cardiac Injury is manifest as asystole (usually with DC current or high voltage) or VF (AC current).

Damage to the myocardium is uncommon but can occur as in skeletal muscle due to heat injury. Rarely coronary spasm has been noted. Spontaneous return of sinus rhythm can be noted after asystole in these cases, but because respiratory paralysis lasts longer, the rhythm may degenerate to VF.

Atrial arrythmias, first and second degree heart block are noted as well as bundle branch blocks. It is postulated that the anterior location of the RCA leaves the sinus and AV nodal arteries more vulnerable. Most ST/T changes resolve.

Nervous System
Nervous System involvement can be diffuse involving both the central nervous system (CNS) and peripheral nervous system (PNS). Spinal cord injury, confusion, paralysis, psychiatric and memory disturbances have been noted. Complications such as intracerebral hemorrhage and spinal fractures should be suspected. Autonomic instability, peripheral vasospasm and depression of the respiratory center can occur. Patients may present with pupils that are fixed and dilated pupils due to autonomic dysfunction. Cataracts occur if the eye is injured and 50% of patients have a ruptured eardrum.

Acute Pharmacotherapies

 * The patient suffering a serious electrical burn or lightning strike is a trauma patient. Resuscitation should first occur in a safe environment.  Cervical spine immobilization and clearance should be performed.  A tetanus shot should be administered.  Coma or or neurologic deficit should prompt brain and/or spine imaging.
 * The survivor of arrest or high-energy injury should have cardiac and hemodynamic monitoring due to the high incidence of arrhythmia and autonomic dysfunction. Creatinine kinase-MB (CK-MB) and electrocardiography are poor measures of myocardial injury.    Troponin use has not been studied.
 * Electrical injuries will require aggressive fluid replacement, while lightning injuries typically require less volume. The patient should be monitored for the development of compartment syndrome, rhabdomyolysis, electrolyte disturbance and renal failure. There is a higher incidence of Curling’s ulcers in electrical burns than other burns.  Persistent ileus usually prompts exploratory laparotomy.  Antibiotic prophylaxis is controversial.  Some give penicillin to cover ‘’Clostridia’’.  Some may require transfer to a burn unit, fasciotomy, extensive skin reconstruction and limb amputation.

Acknowledgements
The content on this page was first contributed by: Resident Report by Duane Pinto, M.D.