When Lightning Strikes

A 54-year-old male is brought in by ambulance after being struck by lightning while wiring a house with grounding poles. He was awake at the scene and does not believe he lost consciousness, but reports a transient episode of bilateral lower extremity weakness. Upon arrival to the ED he complains of persistent bilateral thigh numbness. His primary survey is intact, though he is noted to be mildly tachycardic. He has a punctuate abrasion on the right upper lip and on the volar aspect of the right forearm. His EKG shows isolated T-wave inversions in leads III and aVF. (Figure 1). His creatinine is 1.3, a CK is 764, and his troponin is normal. He is hydrated and admitted for observation. His CK peaks at 1708, but he remains stable overnight and is discharged home the next day.

Background

Electrical shock is a relatively common occurrence with a wide range of severity, ranging from simple static shocks to severe, high-voltage lightning capable of causing immediate death. A basic understanding of electrical injury is important to understanding the injury patterns it causes. Circuits may consist of either an alternating current or a direct current, and injuries are often divided into high voltage (>1,000 volts) or low voltage (<1,000 volts). The hertz encountered in most home circuits cycles with a frequency that matches the muscle cell's ability to contract and relax, thereby potentially causing tetany. This increases the duration of contact and current delivery. Thoracic muscle tetany involving the diaphragm and intercostal muscles can result in respiratory arrest. The repetitive nature of an alternating current also increases the likelihood of current delivery to the myocardium during the vulnerable recovery period of the cardiac cycle, which can precipitate ventricular fibrillation. In contrast, lightning is a direct current, which usually causes a single violent muscle contraction, often thrusting the victim away from the source.

The physics of lightning are far different from man-made electricity. Unlike generated electricity, which is a voltage phenomenon, lightning is a current phenomenon.¹ Probably the most important difference between lightning and high-voltage electrical injuries is the duration of exposure to the current, which also affects the path it takes.² A bolt of lightning has a massive current, usually ranging from 5,000 all the way up to 200,000 amperes, the typical range being between about 10,000 and 50,000. Since these currents are only applied for 10 to 100 ms, energy transfer to the body is therefore limited.³

There are several paths through which lightning may strike an individual. A direct strike is when a lightning bolt makes direct contact with the victim. While most people think first of this mechanism when considering lightning injuries, it is by far the least common. Most frequently, people are injured through ground currents created by a nearby strike. In this mechanism, lightning's subterranean current will preferentially enter a human above ground, typically passing from one leg through the other. This occurs because the resistance of human tissue is usually far less than the resistance encountered underground. Splash strikes and contact injuries make up the rest of lighting-related injuries and have the most potential for large-scale mortality. In splash strikes, the massive electrical current is transferred to a single object so quickly that portions of it branch out (or “splash”) through the air and strike other targets, like in a short-circuit. In contact injuries, individuals in contact with a highly conductive substance (such as a metal rod or structure) that has been struck receive portions of the current discharged in the strike.⁴

Incidence

Estimates regarding risk and epidemiology of lightning-related injuries vary according to the source. About 70% of lightning strikes worldwide are non-fatal, and the annual total number of deaths worldwide is estimated to be between 1,000 and 24,000.^5-7 However, lightning does represent a major weather-related health risk, and was second only to floods in terms of mortality between 1962 and 2002.⁵ It has been estimated that the lifetime risk of any one individual being struck by lightning in a year is low (ranging from 1 in 240,000 to 1 in 960,000), though when accounted for an average length lifespan, the odds of being struck at some point significantly increase to about 1 in 3-12,000.^5,8

In the United States, lightning deaths are highest in Florida and Texas, where topography is generally flat and populations are higher. In contrast to worldwide mortality rates, in the United States fatality from lightning strikes is only about 10%. The total number of fatalities has been declining, down from about 330 per year in the 1940s, to 25-50 per year since 2000. As of Nov. 1 this year, only 26 lightning-related fatalities have been reported in the U.S.^5,9

Scene Safety and Prevention

While there truly are no 100% secure places to hide during a lightning storm, risk can be significantly reduced by staying inside a large building, away from windows. Living structures tend to have metal piping and wiring within the walls that will deflect current away from the occupants, so long as the occupants are not in contact with the internal structure. While a basement tends to be safer, it is recommended that individuals stay away from bare concrete, as it often contains rebar or other metal reinforcing elements that increase the likelihood of electrical current transmission. If a solid structure is not available, a hard-topped vehicle offers the second most effective means of shelter - again so long as the occupant is not in contact with a conductive substance.

Many lightning injuries occur while participating in outdoor activities where adequate shelter is not available. The highest individual risk is seen in those participating in boating and water sports or mountaineering. If along a ridgeline, it is suggested that climbers move to lower ground with less exposure and attempt to stay dry. For those on large bodies of water, it is recommended they return to shore as soon as there is evidence of an impending electrical storm. If this is not possible, the safest location is below deck, if that is an option. Similarly, it is suggested that those participating in scuba activities also return to shore, but, if unable, diving to the deepest safe depth for the longest safe period of time is the recommendation. Many people recommend the 30-30 rule for outdoor safety: If the time from flash to bang is 30 seconds or less, seek shelter for at least the next 30 minutes, or until the storm has clearly passed.⁵

Cardiac Arrest from Lightning Injuries

Mortality from cardiac arrest is lower in lightning strike victims than in the general population.³ The cause of sudden death from a lightning strike is due to both cardiac and respiratory arrest, with the initial rhythm classically being asystole caused by the simultaneous depolarization of all myocardial cells. Ventricular fibrillation can also occur, though it is more common in alternating current electrical injuries. In one small study, only direct strikes created echocardiographic abnormalities, which were at times severe (ejection fraction <15%), though recoverable.¹⁰ Troponin elevations may be detected, unless the strike is limited to the lower extremities, as often occurs in a ground strike.

EKG Changes

Initial findings on EKG may include ST elevation, atrial fibrillation, or a prolonged QT interval (more common with direct strikes), but the most common findings are a new right bundle branch block and T wave inversions.^10,11 Most of these findings resolve within 3-14 days, but may be present as long as 12 months. It is important to note that delayed onset of symptoms and EKG changes have been reported as far out as 3 days.¹⁰ Discharged patients should be counseled to return should they experience new chest pain or shortness of breath. Labile blood pressure and autonomic instability are possible after lightning strikes.¹² According to the Wilderness Medical Society practice guidelines for the prevention and treatment of lightning injuries, it is a Grade IC recommendation to obtain a screening EKG and echocardiogram on high-risk patients.¹³ (Table 1)

TABLE 1. High-Risk Patients¹³

Black Tags and Triage

Lightning strike patients should be approached with a “reverse triage” system, since these cardiac arrest victims typically have a higher survival rate than the general population. Direct electrical injury because of lightning is similar to a single direct current defibrillation. This high-current, high-voltage strike creates a cardiac stunning effect because of massive depolarization, after which the heart often starts spontaneously beating. In addition to cardiac depolarization, the sudden electrical stun can temporarily paralyze the medulla's respiratory center, leading to prolonged apnea, even in the presence of circulatory recovery.¹⁴ If these patients' airways are not secured or breathing not assisted, secondary arrest from hypoxia may occur. For this reason, the standard “START” triage algorithm that would suggest a “black” designation for patients not spontaneously breathing is discouraged. It is a grade 1C recommendation to resuscitate victims without vital signs.¹⁴

Neurologic Manifestations

Neurologic symptoms can range from transient to life-threatening. One particu­larly striking finding occasionally seen is keraunoparalysis. This is a tran­sient paralysis that preferentially affects the lower limbs. It is thought to be the result of overstimulation of the autonomic nervous system resulting in vascular spasm, and it typically resolves within a few hours. Keraunoparalysis can mimic a spinal injury, thus spinal pre­cautions should be maintained and appropriate imaging studies performed as indica­ted. There are more serious neurologic injuries associated with lightning strikes, including lightning-induced intracranial hemorrhage and hypoxic-ischemic encephalopathy. Progressive myelopathy can also result in delayed weakness months after the initial injury.¹⁵

Skin

The rarely-seen Lichtenberg figure is a unique skin finding that is pathognomonic for lightning injury. It is often described as “ferning” or “feathering” on the skin and generally appears within 1 hour and lasts less than 24 hours. While there are some theories, the exact mechanism for how this finding develops is still not certain. No treatment is required; however, further evaluation for other injuries is warranted. Burns are also common with lightning injuries and can occur from direct electrical injury, superheating of metals in contact with the body, or from vaporization of sweat or water on the skin surface. Typically, most burns are superficial and tend to heal quickly. They can be treated with routine burn care.¹⁶

Other Concerns

The most frequently encountered injury associated with lightning strikes is tympanic membrane rupture, which may be present in up to 60% of cases.¹⁷ Uncomplicated ruptures usually heal spontaneously and can be managed conservatively. Ocular injury can also occur, with the lens being the most commonly affected eye structure. Cataract development may occur between 2 days and 4 years after the injury.¹⁸ Sensorineural deafness is also common after a lightning strike, but it is usually transient.¹⁷ It is a grade 1C recommendation to perform an evaluation for tympanic membrane integrity in all lightning strike victims. For any patient with hearing loss, follow-up with an otolaryngologist should be arranged.

With the massive direct current seen in lightning injuries, it is not uncommon for the victim to suffer secondary traumatic injuries, either from being thrown or from massive sudden contraction of large muscle groups. This often leads to long bone injuries and head trauma. A full trauma assessment should be performed on any lightning strike victim.

Post-strike psychiatric and cognitive dysfunction can also occur, and are typically divided into functional or behavioral categories. Functional deficits include abnormalities in memory and concentration, including a reduced capacity for problem solving. Behavioral problems include depression, sleep disturbances, emotional lability, and aggressive behavior. These syndromes typically develop in days to weeks after a lightning strike.¹⁹

Lightning and Pregnancy

Very little data exists regarding lightning strikes in pregnant patients, but it is estimated that fetal mortality approaches 50%. The fetus is likely at higher risk than the mother because it is surrounded by highly conductive amniotic fluid.²⁰ Lightning strikes have been reported to cause uterine rupture and induction of labor. As a result, it is a grade 1C recommendation that pregnant women greater than 20 weeks' gestation who have been struck by lightning should be evacuated to a hospital for lightning-associated injury screening and fetal monitoring. In general, pregnancies less than 20 weeks are not considered viable and do not require fetal monitoring.

The Disposition

Patients suffering a direct lightning strike, or those with an abnormal screening EKG or echocardiogram, should be monitored with telemetry for a minimum of 24 hours.¹⁰ This a grade IC recommendation according to the Wilderness Medical Society practice guidelines for the prevention and treatment of lightning injuries. Other injuries and findings should be addressed at the physician's discretion, and as per standard management.

Conclusion

While often overlooked as a rare disease entity, lightning-related injuries are among the more common weather-related health hazards. A basic understanding of the associated findings and injury patterns is essential for any emergency practitioner, especially those who work in high-strike areas or with high-risk patient populations.

References

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