N. Stuart Harris and David F.M. Brown
Lightning injuries are second only to flooding as the leading cause of weather-related death in the United States (1,4). Lightning is responsible for 75 to 100 deaths per year and as many as 1,000 injuries (1,4). The incidence of lightning injuries parallels the frequency of thunderstorms, with clear seasonal (summer) and daily (afternoon) variations. Victims are most often those who work or play outdoors and are predominantly male (4,8). Although frequent thunderstorms make the Gulf Coast States a leading site of lightning injury, states with major mountain ranges and tidal river basins are also at increased risk (1,8).
Electrical charges in clouds are produced by the movement of ice particles in convective currents, which create a layering of ionic charges: the uppermost cloud gains a net positive charge, and the bottom of the cloud gains a net negative charge (3). The cloud’s negative charge gathers positively charged particles along the ground, creating a large potential difference. Eventually this potential difference becomes so great that the atmosphere’s electrical resistance is overcome and an ionized plasma channel forms. This ionized channel advances from the cloud towards the earth in a downward-branching “stepped leader” pattern at 1/1,000th to 1/2,000th the speed of light. As the stepped leader pattern nears the ground, a “return stroke” ascends from the ground at about one-tenth the speed of light, completing the plasma channel between the cloud and the ground. The channel is now complete, and a massive transfer of electrical charge occurs, producing an instantaneous brightening of the ionized pathway (the visible lightning flash) (3).
Thunder results from the rapid expansion of warmed air and the air’s subsequent contraction and implosion. Although not technically accurate, lightning behaves physiologically as direct current, with an energy level of 2,000 to 2 billion V and 2,000 to 300,000 A (4,8). Although lightning’s voltage and amperage are much higher than conventional electricity, the extremely short duration of lightning contact (0.1 to 1 milliseconds) usually limits cutaneous penetration and commensurate deep tissue injury (4,8). Except for direct strikes, most of the lightning current is thought to “flash over” the outside of the victim, with a relatively limited amount of current leaking internally to interfere with cardiac automaticity, respiratory center function, and autonomic stability (4,8).
There are several major mechanisms of lightning injury. A direct strike occurs when the major pathway of current runs directly through the victim; this results in the highest morbidity and mortality (4,8). When the lightning current strikes an object in contact with the victim, the injury mechanism approximates a direct strike. With “side splash,” current arcs from an object through the air to the victim. “Ground current,” also known as “ground potential,” occurs when lightning strikes the ground and spreads to involve the victim. If ground resistance is greater than the victim’s resistance, current may enter one leg and exit through the other (3). Ground current and side-flash mechanisms are capable of producing multiple casualties.
Associated trauma should be expected and may result from a variety of mechanisms: myotonic extremity or neck contractions, blunt or penetrating injuries from debris or fall, and thermal burns potentially exacerbated by metal jewelry or caused by ignition of clothing.
CLINICAL PRESENTATION
Because of the short duration of lightning exposure, current usually passes over the outside of the body (“flashover” phenomenon), commonly producing superficial or partial-thickness burns (4,8). Pathognomonic fern-like, erythematous patterns known as Lichtenberg figures may be observed (4). Entry and exit wounds and deep internal burns with resultant rhabdomyolysis and myoglobinuria are rare.
The most common cause of death in the lightning victim is cardiopulmonary arrest (CPA) (3,4,8). Internal propagation of the lightning’s electrical potential acts as a massive direct current counter shock, which depolarizes the entire myocardium and causes cardiac asystole (3,4). As a result of cardiac automaticity, an organized electrical rhythm may re-emerge, restoring spontaneous circulation (4). However, primary respiratory arrest as a result of lightning-induced paralysis of the medullary center may occur concomitantly and can outlast cardiac arrest (CA) (3,4,8). Without prompt and prolonged ventilatory support, any return of cardiac rhythm and circulation is likely to deteriorate to hypoxia-induced ventricular fibrillation (3,4). Survivors of lightning exposure can exhibit a variety of cardiac abnormalities, with dysrhythmias and ST–T-wave changes frequently reported (4,7). Acute life-threatening (and often reversible) left-ventricular dysfunction or pericardial tamponade, as demonstrated by echocardiography, has been reported (6,7).
A variety of neurologic effects of lightning injury are frequently encountered. Complete loss of consciousness is common (2,9). In the absence of CPA, consciousness eventually returns, occasionally after a prolonged period. Other common findings include paraplegia, hemiparesis, hemiplegia, localizing sensory deficits, and autonomic dysfunction (2,8,9). The extremities may initially appear cold, mottled, pulseless, and insensitive secondary to vascular spasm and autonomic instability: a phenomenon known as keraunoparalysis (2,4,8). This vasospasm should not be treated with interventions beyond supportive measures.
Virtually all lightning-struck patients have altered mental status and anterograde amnesia; retrograde amnesia is common as well (2,3,4,9). Persistent neuropsychologic, cognitive, and behavioral abnormalities are commonly found (2,8). Intracranial hemorrhage (particularly in the basal ganglia and brainstem), epidural and subdural hematomas, coagulation of brain parenchyma, and thrombosis of vessels have been described (2,3,8,9). Associated trauma may cause cervical spine fracture with spinal cord injury.
Half of patients with lightning injuries have ocular sequelae (4,8). Cataracts are common and may develop in a few days or up to several years after the injury (4,8). Corneal lesions are also common; hyphema, iritis, vitreous hemorrhage, retinal detachment, and optic nerve injury have been described (4,8). Unreactive, dilated pupil(s) as a result of transient autonomic instability may occur and should not be mistaken for a sign of brain death (2,3,8,9).
Tympanic membrane rupture, the most common otologic injury, occurs in 50% of victims of lightning injury and is probably a result of the shock wave of expanding hot air (thunder) during the strike (3,9). Less common findings are hemotympanum, basilar skull fracture, and various acoustic and vestibular sensorineural deficits (4,8,9).
DIFFERENTIAL DIAGNOSIS
Lightning injuries may mimic a range of potentially life-threatening diseases. Neurologic disease processes that can mimic lightning injury include cerebrovascular accidents, seizure disorders, and craniocerebral, spinal cord, or other neurologic trauma (4). Cardiovascular disorders in the differential diagnosis of lightning injury include myocardial infarction, Stokes–Adams attacks, and cardiac dysrhythmias (4,8). The differential should also include toxic ingestions, envenomations, and physical assault. Cutaneous injuries may be misdiagnosed as electrical burns.
As in most clinical situations, the history is crucial to making the correct diagnosis. Obtaining information from bystanders is essential when the victim is incapacitated. Important points include a history of thunderstorm and outdoor occurrence of the accident. Physical examination findings of the arborescent erythematous pattern of Lichtenberg figures are pathognomonic. Tympanic membrane rupture is also highly suggestive.
ED EVALUATION
The history should include a description of events at the scene of injury. Any prehospital interventions and their times should be documented. Present complaints and medical history prior to presentation should also be noted.
The physical examination should focus initially on vital signs; assessment of the airway, breathing, and circulation; and evaluation for trauma and neurologic dysfunction. Serial neurovascular examinations should be performed in patients with signs of peripheral vascular insufficiency. All patients should initially have cardiac monitoring, an electrocardiogram (ECG), and oxygen saturation measurement. Laboratory evaluation can include a complete blood count, serum electrolytes, blood urea nitrogen, creatinine, glucose, and creatine phosphokinase. Urine should be tested for myoglobin. Patients with cardiac dysrhythmias or ischemia, respiratory arrest, or loss of consciousness should have a chest radiograph and cardiac biomarker analysis. Cervical spine radiographs and a cranial computed tomography (CT) scan might be helpful with altered mental status or neurologic deficits. Other radiographs and tests should be obtained as indicated by the history or physical findings.
KEY TESTING
• For all patients: cardiac monitoring, an ECG, and oxygen saturation measurement. Laboratory evaluation should include a complete blood count, serum electrolytes, blood urea nitrogen, creatinine, glucose, and creatine phosphokinase. Urine should be tested for myoglobin.
• For patients with cardiac dysrhythmias or ischemia, respiratory arrest, chest pain, or loss of consciousness: Obtain chest radiograph and cardiac biomarker analysis.
• For patients with altered mental status or neurologic deficits: Consider cervical spine radiographs and a cranial CT scan.
ED MANAGEMENT
Prehospital care of victims with lightning injuries may place initial responders at risk of lightning strike (10). Although acute medical intervention is paramount to reduce mortality, care should be taken to prevent harm to rescuers. Once scene safety has been assured, management should begin with assessment and stabilization of the airway, ventilation, and circulation (10,11). Victims should be treated as trauma patients, with special attention given to cervical spine immobilization. In a mass-casualty event, “reverse triage” should be employed. In a reversal of the usual dictum, rescuers should focus initially on victims in CPA (3,4,8,10,11) because virtually all victims of lightning strike who do not suffer CPA or respiratory arrest survive (4). Standard advanced life-support (ACLS and ATLS) protocols are appropriate however, and aggressive, persistent resuscitative efforts are indicated for all victims, especially those with spontaneous cardiac rhythms and prolonged apnea or coma (4,8,10,11). Ventilatory support may be required for several hours, but, even in these cases, there is potential for full recovery (4,8). Full support should be continued until cerebral function can be assessed.
All patients should initially be given supplemental oxygen, should have intravenous access established, and should be placed on a cardiac monitor. Intravenous fluids should be minimized to reduce any risk of cerebral edema unless hemorrhage, hypotension, or dehydration is evident or rhabdomyolysis is a concern (e.g., with deep or extensive burns or associated crush injury). Although not common, rhabdomyolysis, as indicated by myoglobinuria and elevated serum muscle enzyme levels, may necessitate fluid loading, osmotic diuresis, and urine alkalinization. Standard burn and wound care and tetanus prophylaxis should be given, if appropriate. Patients with cardiac or neurologic abnormalities should have serial ECGs, cardiac biomarker analyses, and routine supportive care. All patients require comprehensive and repeated physical and neurologic examinations.
CRITICAL INTERVENTIONS
• Reverse triage. In a mass-casualty incident involving lightning injury, give the highest priority to patients in cardiac or respiratory arrest when making triage decisions.
• Institute advanced cardiac support measures, and make a prolonged effort to resuscitate patients found pulseless or apneic after a lightning strike.
• Evaluate patients struck by lightning for traumatic injuries.
• Treat keraunoparalysis (cool, potentially pulseless, or numb extremities) conservatively with supportive care.
DISPOSITION
Patients with suspected direct strike or those with cardiac or neurologic abnormalities require admission for at least 24 to 36 hours of observation and continuous cardiac monitoring. Those patients with associated trauma, burns, or rhabdomyolysis also may require admission for their injuries (4,8,11). Patients who have sustained cardiac or respiratory arrest should be admitted to an intensive care unit. Long-term follow-up with neuropsychiatric support is recommended for all patients.
The decision to transfer a patient to another facility depends on the severity of injury and the ability of local resources to provide adequate care. If the necessary services are unavailable, the decision and the timing of transfer should be coordinated with the receiving physician at the nearest appropriate hospital. Emergency personnel with advanced life-support (ALS) capability should accompany the patient.
Common Pitfalls
• Failure to appreciate the difference between lightning injuries and high-voltage injuries.
• Misdiagnosing lightning injury as an isolated cutaneous burn or a primary neurologic or cardiovascular event.
• Misinterpreting unreactive, dilated pupils as a sign of death in patients struck by lightning.
• Failure to admit patients with neurologic complaints or deficits for observation.
REFERENCES
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11. Davis C, Engeln A, Johnson E, et al.; Wilderness Medical Society. Wilderness medical society practice guidelines for the prevention and treatment of lightning injuries. Wilderness Environ Med.2012;23(3):260–269. doi: 10.1016/j.wem.2012.05.016.