Lightning Injuries: Background, Etiology, Epidemiology

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Lightning Injuries Updated: Nov 20, 2017 Author: Mary Ann Cooper, MD; Chief Editor: Joe Alcock, MD, MS more...

OVERVIEW

Background For over a century, lightning injuries had been the second most common cause of storm-related death in the United States. They are now third, behind flash floods and tornados. [1, 2, 3] Although National Oceanic and Atmospheric Administration (NOAA) data showed as many as 3,000 deaths and nearly 10,000 casualties from lightning in the years from 1959-1994, the annual death rate has decreased to less than 0.1 case per million for the last 5 years, owing to public education by the media and the members of the Lightning Safety Week team. [2] While it is highly likely that all US deaths are recorded as a result of improved media coverage, the actual number of lightning casualties may be higher, because up to 50% may go unreported. [2] Nevertheless, in most years, lightning kills more people each year in the United States than hurricanes, volcanoes, and earthquakes combined. [4] (See Epidemiology and Etiology.) Far more injuries and deaths occur in tropical and subtropical developing countries (see Epidemiology and Etiology), and newspaper reports frequently list multiple injuries and deaths in each event. Complicating the increased risk people in these countries have because of higher lightning density (lightning strikes/km2/year), lightning-unsafe housing, and greater everyday exposure are the folk beliefs that may prevent adequate prevention and mitigation. People in many countries believe in two kinds of lightning: "natural lightning" and "man-made lightning" that can be called down by witches or can be prevented with charms, herbs, or burying something under a structure as it is being built. [5, 6] In Zambia, it is believed that wearing the color red attracts lightning. Others believe that anyone injured by lightning has been cursed, shunning them and their family. Families may believe their only recourse is to move and start over in a village where their history is unknown. [7] For most thunderstorms, 70-90% of lightning strikes are intracloud or from cloud to cloud. From 10-30% of lightning can be cloud to ground (CG), depending on the storm. Lightning strikes the earth more than 100 times each second and 8 million times per day. Worldwide, approximately 50,000 thunderstorms occur per day that may result in forest fires, injury to animals and people, and/or damage to electrical and communications lines and electronics, leading to millions of dollars in downtime for businesses. Everyone is a potential victim. In the United States, cloud-to-ground lightning strikes occur approximately 30 million times each year. [8] Lightning strikes in the United States are most common in Florida, the Atlantic coast, and along the southeastern coast of the Gulf of Mexico. [9] The National Weather Service (NWS) estimates that 100,000 thunderstorms occur in the United States each year. Lightning is evident in all thunderstorms. The danger of lightning may not be apparent to an individual because lightning can strike 10 miles or more away from the rain of a thunderstorm. [4] (See Epidemiology.) Lightning starts with short (30-50 m) spurts of static energy in a cloud. The lightning retreats back to its origin, refills the original channel, and branches at the end of the original channel to make a second generation of 30- to 50-m channels. Lightning continues with the retreats and new generations until the charge is either expended (intracloud lightning) or randomly works its way downward as a CG flash. [10] Any object near the intense electrical field of a thundercloud will have an opposite charge induced in it, be it a television tower, a tree, a person, or a blade of grass. Multiple upward leaders of current rise from these objects. Most do not contact the main lightning channel but may have sufficient energy to cause significant injury (Cooper upward streamer). Eventually, the downward leader may join one or more of the upward streamers to complete the lightning channel. At that point, a return stroke fills all of the branches and the lightning becomes visible. Lightning has more than one ground contact about 30-50% of the time. Only three factors predispose to a lightning hit: height of an object, isolation, and "pointiness," which is not a factor with people. However, while lightning has a tendency to hit the tallest object, this 30- to 50-m radius from the last branch point means that tall objects, such as a mountaintop half a mile away, a television tower 300 yards away, a tree 75 yards away, or even the goal posts on a football field, are outside the range for protecting anyone (ie, the field's goalposts are unlikely to protect someone standing in the middle of a football field if lightning is coming down over the person's head). There are multiple instances and videos of strike points to cars passing tall telephone or electrical poles and other hits where lightning seems to “ignore” the height rule. [10] (See Etiology and Prevention.) With all these data, it must be realized that while lightning science strives to describe and explain it, mostly in a statistical manner, these are not rules governing its behavior. Lightning is capricious and random, and any individual strike may defy common public assumptions. Although most injuries occur outdoors, a few people are injured indoors every year from contact injuries with plumbing or landline telephone–mediated strikes. [11, 12] While use of cell phones, iPods, and other portable electronic devices may change the pathway of lightning around a person, it does not increase the risk of injury except by distracting the individual from paying attention to warning signs, such as storm clouds and thunder. In fact, the worldwide availability of cell phones is offering an ideal opportunity for texted or tweeted severe weather warnings and other public education. [6, 13] The most important characteristic features of lightning injuries are multisystem, primarily neurologic, injuries and widely variable severity. This article discusses the physics of lightning and the pathophysiology and treatment of lightning injuries. [14] Because persons struck by lightning have a better chance of survival than persons who experience cardiopulmonary arrest from other causes, resuscitation for persons struck by lightning must be instituted immediately, followed by a comprehensive treatment program of the other systemic manifestations. [15] (See Prognosis, Presentation, and Treatment.) In 2017, a proposal for an American Psychiatric Association Diagnostic and Statistical Manual (DSM) classification of postelectrical and postlightning injury syndrome was published. [16]

Types of injuries Injuries range from tiny static electricity–like exposures to cardiac arrest. [10, 17, 18, 19, 20] No good statistics are available for the distribution of severity across the injured population. Few individuals experience the full energy of a lightning strike because only about 3-5% of injuries are from a direct strike. [21] Most of the energy is mediated by other factors, including the ground, a tree, or other object that, once hit, transmits the energy to the person. In fact, fewer than half of affected persons have signs of burns or any other marks. When burns do occur in developed countries, they are usually superficial. In addition to electrical injury, many may suffer concussive blunt force trauma if they are close to the strike point. [22] Internal burns or deep burns, such as occur with high-voltage electrical injury, are rare. In developing countries, severe burns are reported much more frequently. It is unclear if these are sampling bias, if reports are inflated by journalists who hear the story several times removed from the incident and expect the victims to be “charred beyond recognition,” if the mechanisms and physical damage are somehow different, or if the injuries appear to be more severe owing to delayed access to good medical care. [23] Ninety percent of sub-Saharan housing, usually mud brick with thatch or sheet metal roofs, is not lightning safe. Keraunoparalysis, a temporary paralysis after lightning injury that may last for minutes to hours, may keep even healthy individuals from escaping their home as the overhead thatch, ignited by lightning, burns and falls on them. [23] Myoglobinuria is rarely caused by lightning, whereas cardiac and respiratory arrest, vascular spasm, neurologic damage, and autonomic instability are more common. [24] Blunt force injuries may occur from falling, being thrown by muscle contractions, or barotrauma from the explosive force of a nearby lightning strike. [10] Occasionally, a person may receive secondary shrapnellike injuries by being hit by pavement or bits of an exploded tree. [25] Lightning strikes are primarily a neurologic injury that affects all three components of the nervous system: central, autonomic, and peripheral.

Classification of lightning injuries Because exposure to the effects of lightning can be so variable in mechanism and intensity, it is useful to characterize lightning injuries as mild, moderate, or severe. Mild lightning injury is rarely associated with superficial burns, but persons struck often report loss of consciousness, amnesia, confusion, tingling, and numerous other nonspecific symptoms. Lightning burns are invariably superficial and have little or no deep-tissue damaging effects. Provided the patient is stable and there are no contraindications such as chest pain, hypotension, or continuing mental status changes, many of these patients can be released home with reliable caretakers. Since there is little known at this time that can be done to mitigate the outcome and sequelae, there is usually little benefit to hospitalization. Moderate lightning injury may cause seizures, respiratory arrest, or cardiac standstill, which spontaneously resolves with resumption of normal cardiac activity. Much of the symptomatology mirrors that of mild lightning injury, except superficial burns are much more common, both initially and in a delayed fashion. These patients may have lifelong symptoms of brain injury, chronic pain, irritability, and sleep disorders. There is still little that hospitalization can offer these patients except careful monitoring for acute complications connected to the initial manifestations. Patients with severe lightning injury usually present with cardiopulmonary arrest, often complicated by a prolonged period in which they did not receive CPR. The delay may be because the individuals are in an isolated location when injured or because of the myth that the person retains an electrical charge, making him or her dangerous to touch. Survival is rare in this group unless a bystander begins CPR immediately. There have been rare cases of recovery from this more severe group but usually only after prolonged ICU and rehabilitative care. Additionally, as noted above, victims in developing countries may have more severe burns resulting from keraunoparalysis and burns by secondary fire.

Physics of lightning Lightning is a natural atmospheric electrical discharge that occurs between regions of net positive and net negative electrical charges. It is dependent on a complex interaction of updrafts, moisture, atmospheric instability, temperature, and other factors. Readers with a special interest in this are referred to the NOAA article Understanding Lightning for a thorough but understandable discussion with animations. Lightning There are two basic types of lightning: cloud-to-cloud or intracloud (CC) and cloud-to-ground (CG). A lightning flash is initiated by an electrical breakdown between the positive and negative charge regions in a cloud. Sixty to 90% of lightning is intracloud. When the flash turns towards the ground, a barely visible downward leader descends in regular steps, typically 30-50 m long at intervals of 0.05 ms in a downward, branching fashion toward the ground. This initial flow of electricity, the leader stroke, reaches the ground in approximately 20 ms. The diameter of the stepped leader ranges from a few centimeters to a few meters, depending on what parameter is measured. Within the leader is a current-carrying core 1-2 cm in diameter. As the branching process nears the ground, an upward discharge, termed the upward leader, completes the path of ionization approximately 30-50 m above the ground. At this moment of attachment, the cloud is short-circuited to the ground, and the major electrical discharge, a luminous return stroke of high current, occurs. Following the initial stroke, secondary leader and return strokes frequently occur. See Lightning Safety for many other interesting facts about lightning. Thunder Air that is crossed by lightning is heated rapidly, and the cylindrical column expands at supersonic speeds. Within 1-2 meters, the shockwave decays to a sound wave called thunder. Thunder comes from the entire lightning channel length, producing a mixture of different tones that are further modified as it spreads outward. Thunder rarely is heard at distances greater than 10 miles because of such factors as terrain, atmospheric temperature, wind shear, large intervening structures, and urban noise. The power of lightning is awesome, an estimated 10,000-200,000 amperes (A) of current and 20 million to 1 billion volts. A current of 100,000 A can shift blocks of stone weighing 5 tons, and rocks weighing 50 pounds may be thrown 20 yards or more. Types of lightning CG lightning, described earlier, is the most frequent type of lightning and accounts for human injuries. Another type, sheet lightning, travels within a cloud and gives the cloud the appearance of a white sheet. “Heat lightning” is a misnomer for lightning that does not appear to be connected with rain and is usually far enough away to make a wonderful show. It is equally as dangerous as any other form of lightning and can turn into deadly cloud-to-ground lightning just as easily. Several rare forms of lightning are ribbon and bead lightning. These are forms of cloud-to-ground discharge with a flash consisting of several strokes. Ribbon lightning occurs when the channel is blown perpendicular to the line of sight by the wind, displacing subsequent strokes. Consequently, the flash appears as a ribbon of several strokes. In bead lightning, the main lightning flash breaks into luminous sections, or beads, as the light intensity of the channel decays. The most rare and mysterious form of lightning is ball lightning. [26] A mix of fire and electricity concentrated in a fireball with a diameter of 10-30 cm, ball lightning usually appears suddenly, even in indoor conditions, during a thunderstorm. It moves quickly for several meters, can change direction, and ultimately disappears sometimes soundlessly and other times with a pop or larger explosive sound. It has a life span of several seconds, and its color is quite variable but most commonly described as white, yellow, or orange.

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Lightning Injuries: Background, Etiology, Epidemiology

Lightning Injuries Updated: Nov 20, 2017 Author: Mary Ann Cooper, MD; Chief Editor: Joe Alcock, MD, MS more... OVERVIEW Background For over a centur...

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