# Seminar 10: Environmental Emergencies

## Emergency Medicine Clerkship

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## Learning Objectives

By the end of this seminar, students will be able to:

1. Classify heat-related illness along its clinical spectrum and implement rapid cooling strategies for heat stroke patients to prevent multi-organ failure
2. Recognize the physiologic stages of hypothermia, select appropriate rewarming methods based on severity, and manage cardiac arrest in the hypothermic patient
3. Evaluate and manage drowning victims with attention to hypoxia as the primary mechanism of morbidity, and apply evidence-based prognostic factors to guide resuscitation
4. Identify venomous snakebites endemic to North America, distinguish pit viper from coral snake envenomation, and administer appropriate antivenom therapy
5. Differentiate acute mountain sickness from high altitude pulmonary edema and high altitude cerebral edema, and initiate pharmacologic and descent-based treatment
6. Assess and manage electrical and lightning injuries including recognition of unique injury patterns, indications for cardiac monitoring, and resuscitation principles

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## Seminar Outline

### Section 1: Heat-Related Illness

Heat-related illness encompasses a clinical spectrum ranging from mild heat cramps to life-threatening heat stroke. Heat cramps represent the mildest form and manifest as painful muscle spasms during or after physical exertion in hot environments, resulting primarily from sodium and fluid losses through sweating. Heat exhaustion occupies the middle of the spectrum and presents with fatigue, nausea, headache, dizziness, and profuse sweating, with core body temperature remaining below 104 degrees Fahrenheit (40 degrees Celsius). Critically, patients with heat exhaustion maintain normal central nervous system function, and this distinction separates heat exhaustion from the far more dangerous heat stroke.

Heat stroke is defined by a core body temperature exceeding 104 degrees Fahrenheit (40 degrees Celsius) in combination with central nervous system dysfunction, which may manifest as confusion, agitation, seizures, or coma. Two clinical variants are recognized. Classic heat stroke occurs predominantly in elderly individuals and those with chronic medical conditions, often in the setting of enclosed spaces or heat waves, and is classically associated with anhidrosis (absence of sweating). Exertional heat stroke affects younger, physically active individuals such as athletes and military recruits, and these patients may still be diaphoretic despite critically elevated temperatures. Cardiovascular stress manifests as tachycardia and, in advanced cases, hypotension from dehydration and vasodilation.

Rapid cooling is the cornerstone of heat stroke management and must begin immediately upon recognition. Cold water immersion is the most effective method, achieving cooling rates of up to 0.2 degrees Celsius per minute, and should be employed whenever feasible. Evaporative cooling, which involves misting the patient with water while directing fans across the skin to promote evaporation, is an effective and widely accessible alternative. Ice packs placed in the axillae, groin, and at the sides of the neck target areas of high blood flow and provide adjunctive cooling. Additional methods include cooling blankets and administration of intravenous cold saline as adjuncts. The cooling target is a core temperature below 39 degrees Celsius (102.2 degrees Fahrenheit), at which point active cooling should be slowed or stopped to avoid overshooting into hypothermia.

The management of heat stroke extends beyond cooling to include comprehensive supportive care. Airway protection takes priority in patients with altered mental status who cannot protect their airway. Aggressive intravenous fluid resuscitation with normal saline addresses dehydration, though caution is warranted in elderly patients who may be susceptible to volume overload. Benzodiazepines should be administered to control shivering, which generates additional metabolic heat and counteracts cooling efforts. Continuous monitoring of core temperature, serum electrolytes, and renal function is essential because heat stroke frequently precipitates multi-organ dysfunction including rhabdomyolysis, disseminated intravascular coagulation, acute kidney injury, and hepatic injury. All patients with heat stroke require intensive care unit admission for ongoing monitoring and management.

<image>Panel A: Clinical spectrum diagram showing progression from heat cramps through heat exhaustion to classic and exertional heat stroke with corresponding temperature thresholds and distinguishing features. Panel B: Photograph of cold water immersion technique for heat stroke with a patient placed in an ice-water bath and temperature monitored via rectal probe. Panel C: Illustration of evaporative cooling setup demonstrating strategic misting and fan placement with ice packs positioned at the axillae, groin, and neck. Panel D: Multi-organ dysfunction diagram showing the systemic complications of heat stroke including rhabdomyolysis, disseminated intravascular coagulation, acute kidney injury, and hepatic failure.</image>

### Section 2: Hypothermia

Hypothermia is classified by severity based on core body temperature, and each stage carries distinct physiologic consequences and management implications. Mild hypothermia, defined as a core temperature between 32 and 35 degrees Celsius (89.6 to 95 degrees Fahrenheit), is characterized by vigorous shivering as the body attempts to generate heat, along with tachycardia, tachypnea, and mild confusion. Moderate hypothermia, with core temperatures between 28 and 32 degrees Celsius (82.4 to 89.6 degrees Fahrenheit), is marked by the cessation of shivering as thermoregulatory mechanisms fail, bradycardia, atrial fibrillation, and increasing lethargy. Severe hypothermia, defined as a core temperature below 28 degrees Celsius (82.4 degrees Fahrenheit), produces coma, muscular rigidity, ventricular fibrillation or asystole, and the appearance of clinical death.

Clinical recognition of hypothermia requires a high index of suspicion, particularly in vulnerable populations including the elderly, homeless individuals, and those with substance intoxication. The mental status deteriorates progressively from confusion and lethargy in mild hypothermia to obtundation and coma in severe cases. Electrocardiographic findings include the pathognomonic Osborn wave (J wave), a distinctive deflection at the junction of the QRS complex and ST segment, along with progressive prolongation of all intervals and susceptibility to atrial and ventricular arrhythmias. The respiratory rate decreases as core temperature drops. Shivering, a reliable sign in mild hypothermia, is notably absent in severe hypothermia. Pupils may become dilated and fixed, mimicking brain death, but this finding is reversible with rewarming and must not be used as a criterion for terminating resuscitation.

Rewarming strategies are matched to the severity of hypothermia. Mild hypothermia is treated with passive external rewarming, which involves removing the patient from the cold environment, removing wet clothing, and applying blankets in a warm room to allow the body's endogenous heat production to restore normal temperature. Moderate hypothermia requires active external rewarming using forced warm air devices (such as a Bair Hugger), heated blankets, and warm packs. Severe hypothermia demands active internal rewarming, which includes warmed intravenous fluids (normal saline heated to 40 to 42 degrees Celsius), warm body cavity lavage (bladder, pleural, peritoneal), and, in the most critically ill patients, extracorporeal membrane oxygenation (ECMO) or cardiopulmonary bypass. Throughout the rewarming process, patients must be handled gently because the hypothermic myocardium is extremely irritable, and rough handling, jostling, or aggressive movement may precipitate ventricular fibrillation.

Cardiac arrest in the hypothermic patient presents unique challenges that demand modifications to standard resuscitation algorithms. The guiding principle is that a hypothermic patient should not be declared dead until they are warm and dead, as successful resuscitation has been documented even after prolonged arrest in the setting of deep hypothermia. Defibrillation may be ineffective at very low core temperatures, and current guidelines recommend attempting defibrillation but limiting to three shocks until the core temperature has been raised above 30 degrees Celsius. Resuscitation medications may accumulate unpredictably in the hypothermic patient due to decreased hepatic and renal clearance, so doses should be spaced at longer intervals. ECMO is the most effective rewarming modality in cardiac arrest, providing both circulatory support and rapid core rewarming. A target core temperature of 32 to 34 degrees Celsius should generally be achieved before considering termination of resuscitation efforts.

<image>Panel A: Classification diagram showing the three stages of hypothermia with corresponding core temperature ranges, physiologic responses, and associated cardiac rhythms. Panel B: Electrocardiogram strip demonstrating the characteristic Osborn (J) wave at the junction of the QRS complex and ST segment in a hypothermic patient. Panel C: Rewarming strategy algorithm matching passive external, active external, and active internal rewarming methods to mild, moderate, and severe hypothermia classifications. Panel D: ECMO circuit diagram illustrating extracorporeal rewarming for hypothermic cardiac arrest with venous drainage, oxygenation, heat exchange, and arterial return.</image>

### Section 3: Cold Injuries

Frostbite represents tissue freezing and is classified into four degrees based on depth of injury, analogous to burn classification. First-degree (superficial) frostbite involves only the epidermis and presents with numbness, erythema, and edema of the affected area, with full recovery expected. Second-degree (superficial partial-thickness) frostbite extends into the dermis and is characterized by the formation of clear, fluid-filled blisters overlying erythematous skin. Third-degree (deep partial-thickness) frostbite penetrates into the subcutaneous tissue and produces hemorrhagic blisters filled with blood-tinged fluid, indicating deeper vascular injury. Fourth-degree (full-thickness) frostbite involves muscle, tendon, and bone, resulting in tissue necrosis, mummification, and the potential need for amputation.

The management of frostbite begins with removal from the cold environment, with the critical caveat that tissue that has been thawed must never be allowed to refreeze, as refreezing causes far more extensive tissue damage than the initial freezing injury. Rapid rewarming is accomplished by immersing the affected extremity in warm water maintained at 37 to 39 degrees Celsius (98.6 to 102.2 degrees Fahrenheit), a process that typically requires 30 to 60 minutes until the tissue becomes soft and pliable. Rewarming is intensely painful, and adequate analgesia with opioid medications is usually necessary. Clear blisters should be debrided because the blister fluid contains inflammatory mediators that promote further tissue damage, while hemorrhagic blisters should be left intact to avoid disruption of deeper tissue. Tetanus prophylaxis should be updated as indicated.

Adjunctive treatments for severe frostbite aim to improve perfusion and reduce tissue loss. Tissue plasminogen activator (tPA) has shown promise when administered within 24 hours of injury at specialized centers, as thrombolysis of microvascular clots may restore perfusion to threatened tissue. Iloprost, a prostacyclin analog, has demonstrated benefit in improving outcomes for severe frostbite. Nonsteroidal anti-inflammatory drugs are administered to reduce inflammation and inhibit thromboxane-mediated vasoconstriction. Topical aloe vera is applied to debrided surfaces for its anti-inflammatory properties. Elevation of the affected extremity reduces edema. Surgical intervention, including debridement or amputation, should be delayed for weeks to months until clear demarcation between viable and nonviable tissue has been established, as the initial appearance often overestimates the extent of tissue loss.

Non-freezing cold injuries represent a distinct category of cold-related tissue damage that occurs at temperatures above freezing. Chilblains (pernio) are inflammatory lesions that develop after exposure to cold and damp conditions, presenting as tender, pruritic, erythematous to violaceous papules and plaques on the fingers, toes, ears, or nose. Trench foot (immersion foot) results from prolonged exposure to wet conditions at cool but above-freezing temperatures, leading to vascular damage, neuropathy, and tissue breakdown. The affected feet appear pale, cool, and edematous, and patients report numbness followed by intense burning pain during rewarming. Treatment for non-freezing cold injuries involves gentle rewarming, elevation of the affected extremities, transition to dry conditions, and symptomatic management with analgesics. Nifedipine may be beneficial for recurrent chilblains.

<image>Panel A: Clinical photographs demonstrating the four degrees of frostbite from first-degree erythema and edema through fourth-degree tissue necrosis and mummification of digits. Panel B: Illustration of the warm water immersion technique for frostbite rewarming showing the affected hand submerged in water at 37-39 degrees Celsius with a thermometer monitoring bath temperature. Panel C: Comparison photographs of clear blisters (to be debrided) and hemorrhagic blisters (to be left intact) in second-degree and third-degree frostbite. Panel D: Clinical images of non-freezing cold injuries showing violaceous papules of chilblains on the toes and the pale, edematous appearance of trench foot.</image>

### Section 4: Drowning

The pathophysiology of drowning centers on hypoxia as the primary mechanism of morbidity and mortality, regardless of whether the submersion occurred in fresh water or salt water. When water enters the airways, even in small amounts, it disrupts the surfactant layer that maintains alveolar surface tension, leading to atelectasis, ventilation-perfusion mismatch, and intrapulmonary shunting. Pulmonary edema develops rapidly as alveolar capillary membranes are damaged by the combined effects of hypoxia and direct fluid injury. Aspiration of contaminated water introduces pathogens and foreign material into the lungs, increasing the risk of subsequent pneumonia. Although historical teaching emphasized differences between fresh water and salt water drowning based on osmotic effects, the clinical management is essentially identical regardless of water type.

The management of drowning begins with rescue and immediate initiation of resuscitation. Rescue breathing can be initiated in the water by trained rescuers, as oxygenation is the highest priority. Standard cardiopulmonary resuscitation should begin as soon as the victim is removed from the water; abdominal thrusts (the Heimlich maneuver) have no role in drowning management and should not be performed. Cervical spine precautions are indicated only when the mechanism suggests a high risk of spinal injury, such as diving into shallow water or high-velocity watercraft accidents, and should not delay resuscitation. Concurrent hypothermia is common in drowning victims and should be treated with appropriate rewarming measures. Patients with altered mental status or persistent hypoxia require endotracheal intubation and mechanical ventilation with positive end-expiratory pressure (PEEP) to recruit collapsed alveoli and improve oxygenation.

Prognostic factors in drowning help guide the intensity and duration of resuscitative efforts. Shorter submersion times are associated with better neurologic outcomes, while submersion exceeding 25 minutes in warm water carries an extremely poor prognosis. Colder water temperature is protective because hypothermia reduces cerebral metabolic oxygen demand, and there are well-documented cases of neurologically intact survival after prolonged cold water submersion, particularly in children. Witnessed events with rapid rescue and bystander cardiopulmonary resuscitation significantly improve survival. Children may tolerate longer submersion times than adults due to the diving reflex and proportionally greater body surface area promoting rapid cooling. Drowning in swimming pools carries a better prognosis than open water drowning due to typically shorter submersion times, warmer water, and faster rescue.

Disposition decisions in drowning depend on the severity of the submersion event and the patient's clinical status. Asymptomatic patients with normal oxygen saturation and no respiratory symptoms should be observed in the emergency department for a minimum of 4 to 8 hours, as delayed deterioration can occur from progressive pulmonary edema. Any patient with respiratory symptoms, including cough, dyspnea, or abnormal auscultatory findings, should be admitted for ongoing monitoring and treatment. Patients with significant hypoxia, hemodynamic instability, or altered mental status require intensive care unit admission. Cardiac arrest from drowning carries a poor prognosis overall, though pediatric patients, particularly those with cold water submersion, may have better outcomes, justifying aggressive and prolonged resuscitative efforts in this population.

<image>Panel A: Pathophysiology diagram showing the cascade from water aspiration through surfactant disruption, atelectasis, ventilation-perfusion mismatch, and development of pulmonary edema. Panel B: Drowning management algorithm from rescue and rescue breathing through CPR initiation, airway management, and hypothermia treatment. Panel C: Chest radiograph demonstrating bilateral pulmonary edema in a near-drowning victim with corresponding arterial blood gas showing hypoxemia. Panel D: Prognostic factors chart displaying submersion duration, water temperature, witness status, bystander CPR, and patient age with their respective impacts on outcome.</image>

### Section 5: Altitude Illness

Acute mountain sickness is the most common form of altitude illness and typically occurs when individuals ascend rapidly to altitudes above 2,500 meters (approximately 8,000 feet) without adequate acclimatization. The cardinal symptom is headache, which must be accompanied by at least one additional symptom such as nausea, vomiting, fatigue, dizziness, or sleep disturbance to meet diagnostic criteria. The Lake Louise scoring system provides a standardized method for assessing symptom severity and is widely used in research and clinical practice. Prevention is achieved through gradual ascent, limiting altitude gain to no more than 300 to 500 meters per day above 2,500 meters, and prophylactic acetazolamide at doses of 125 to 250 milligrams twice daily. Treatment involves cessation of further ascent, rest, analgesics for headache, and descent if symptoms worsen despite conservative measures.

High altitude pulmonary edema (HAPE) is a potentially fatal form of noncardiogenic pulmonary edema that typically develops 2 to 4 days after arrival at altitude, most commonly above 3,000 meters. The pathophysiology involves exaggerated hypoxic pulmonary vasoconstriction, leading to uneven distribution of blood flow, capillary stress failure, and fluid leakage into the alveolar spaces. Patients present with progressive dyspnea, initially with exertion and subsequently at rest, nonproductive cough that may progress to production of pink or blood-tinged sputum, and exercise intolerance. Physical examination reveals tachycardia, tachypnea, and bilateral crackles on auscultation. The definitive treatment is descent, even a relatively modest descent of 500 to 1,000 meters can produce dramatic improvement. Supplemental oxygen, when available, is an effective adjunct, and nifedipine serves as the pharmacologic treatment by reducing pulmonary artery pressure through vasodilation. A portable hyperbaric chamber (Gamow bag) can simulate descent when physical descent is not immediately feasible.

High altitude cerebral edema (HACE) represents the most severe and immediately life-threatening form of altitude illness, resulting from vasogenic cerebral edema due to breakdown of the blood-brain barrier under hypoxic conditions. The hallmark presentation is ataxia, which is the earliest and most reliable clinical sign, progressing to altered mental status, confusion, drowsiness, and eventually coma if untreated. HACE may develop de novo or evolve from worsening acute mountain sickness. The treatment demands immediate descent, which is the definitive and most important intervention. Supplemental oxygen should be administered concurrently. Dexamethasone is the pharmacologic treatment of choice, given as an 8-milligram loading dose followed by 4 milligrams every 6 hours, and acts by reducing cerebral edema through anti-inflammatory and membrane-stabilizing effects.

The pharmacologic management and prevention of altitude illness relies on several key medications with distinct mechanisms and indications. Acetazolamide, a carbonic anhydrase inhibitor, is the primary preventive medication and works by inducing a metabolic acidosis that stimulates ventilation, thereby improving oxygenation at altitude. It is dosed at 125 to 250 milligrams twice daily beginning 24 hours before ascent. Dexamethasone is reserved for treatment of HACE and as an adjunct in severe acute mountain sickness, rather than routine prophylaxis. Nifedipine, a calcium channel blocker, is the treatment of choice for HAPE due to its pulmonary vasodilatory effects, typically given as 30 milligrams extended-release every 12 hours. Phosphodiesterase inhibitors including tadalafil and sildenafil also reduce pulmonary artery pressure and have demonstrated efficacy in both prevention and treatment of HAPE, serving as alternatives or adjuncts to nifedipine.

<image>Panel A: Altitude illness spectrum diagram showing acute mountain sickness, HAPE, and HACE with their respective altitude thresholds, timelines, and pathophysiologic mechanisms. Panel B: Chest radiograph demonstrating bilateral patchy infiltrates characteristic of high altitude pulmonary edema in a climber presenting at altitude. Panel C: Illustration of the Gamow portable hyperbaric chamber with a patient inside, showing the hand pump mechanism and pressure gauge. Panel D: Pharmacologic management summary showing acetazolamide for prevention, nifedipine and phosphodiesterase inhibitors for HAPE, and dexamethasone for HACE with dosing regimens and mechanisms of action.</image>

### Section 6: Snake Envenomation

Pit vipers of the subfamily Crotalinae represent the most clinically significant venomous snakes in North America and include rattlesnakes, copperheads, and cottonmouths (water moccasins). These snakes are identified by their characteristic heat-sensing pit organs located between the eye and nostril, elliptical pupils, and triangular head shape. Pit viper venom is a complex mixture of hemotoxic and cytotoxic enzymes that cause local tissue destruction, coagulopathy, and systemic effects. Local effects include progressive pain, swelling, and ecchymosis that may spread proximally from the bite site over hours. Systemic effects include coagulopathy with hypofibrinogenemia, thrombocytopenia, and bleeding, as well as hypotension from increased capillary permeability and third-spacing of fluids.

The management of pit viper envenomation begins with immobilization of the affected extremity and patient stabilization. Large-bore intravenous access should be established in an unaffected limb, and initial laboratory studies include a complete blood count, coagulation profile including fibrinogen, and type and screen. CroFab (crotalidae polyvalent immune Fab) is the antivenom of choice and is indicated for progressive local tissue effects, systemic signs including coagulopathy or hypotension, and laboratory evidence of venom effects. The initial dose is typically 4 to 6 vials administered intravenously, with additional doses given as needed based on clinical response and laboratory trends. It is critical to avoid interventions that have been shown to be harmful, including tourniquet application, application of ice, and incision and suction at the bite site, all of which worsen outcomes and delay appropriate care.

Coral snakes (family Elapidae) are the other medically significant venomous snakes in the United States and possess a fundamentally different venom profile than pit vipers. They are identified by their distinctive color banding pattern, with the mnemonic "red touches yellow, kill a fellow" distinguishing the venomous coral snake from harmless mimics. Coral snake venom is primarily neurotoxic, containing phospholipase A2 and other neurotoxins that block neuromuscular transmission at the postsynaptic nicotinic receptor. Symptoms may be delayed for hours after the bite and include bulbar symptoms such as ptosis, dysphagia, and dysarthria, progressing to respiratory paralysis. Because of this delayed onset, antivenom should be administered for all confirmed coral snake bites even in asymptomatic patients. Close respiratory monitoring with preparation for endotracheal intubation and mechanical ventilation is essential.

Exotic snake envenomation, while uncommon, may be encountered in emergency departments near zoological facilities or in areas where private ownership of venomous reptiles is legal. The immediate priority is to contact the regional poison control center, which maintains databases of antivenom availability and can coordinate transfer of specific antivenoms from zoos, antivenin repositories, and other sources. If safe to do so, obtaining a photograph of the snake assists with species identification, which is essential for selecting the appropriate antivenom. Supportive care, including intravenous fluid resuscitation, vasopressor support, blood product administration, and airway management, should be provided while awaiting specific antivenom. The treating physician should not delay supportive measures while awaiting antivenom availability.

<image>Panel A: Identification features of North American pit vipers showing the heat-sensing pit organ, elliptical pupil, triangular head shape, and comparison photographs of rattlesnake, copperhead, and cottonmouth. Panel B: Clinical photographs demonstrating progressive local effects of pit viper envenomation including swelling, ecchymosis, and tissue necrosis at sequential time points after the bite. Panel C: Color banding pattern comparison between the venomous coral snake (red touches yellow) and the harmless king snake mimic (red touches black). Panel D: Envenomation management algorithm showing initial assessment, laboratory evaluation, antivenom indications for pit vipers (CroFab) and coral snakes, and monitoring protocols.</image>

### Section 7: Other Bites and Stings

Hymenoptera stings from bees, wasps, hornets, and fire ants are the most common cause of envenomation-related anaphylaxis and death in the United States. Local reactions produce pain, erythema, and swelling at the sting site and are managed with stinger removal (by scraping rather than squeezing to avoid injecting additional venom), application of ice, and oral antihistamines. Large local reactions involve swelling extending beyond 10 centimeters from the sting site and may benefit from a short course of oral corticosteroids in addition to antihistamines. Anaphylaxis from hymenoptera stings presents with urticaria, angioedema, bronchospasm, and cardiovascular collapse, and demands immediate treatment with intramuscular epinephrine, aggressive airway management, intravenous fluids, and antihistamines. Multiple simultaneous stings, even in non-allergic individuals, may cause systemic toxicity from the cumulative venom load, including rhabdomyolysis, hemolysis, and renal failure. All patients with anaphylactic reactions should be referred to an allergist for venom immunotherapy evaluation.

Spider bites from two medically significant species in North America warrant distinct clinical approaches. Black widow spider (Latrodectus) bites produce a syndrome of severe muscle cramping and rigidity, particularly affecting the abdomen and back, due to the neurotoxin alpha-latrotoxin, which causes massive release of acetylcholine and norepinephrine at nerve terminals. Treatment consists of benzodiazepines for muscle spasm, opioid analgesics for pain, and antivenom (Latrodectus antivenin) for severe cases with uncontrolled symptoms. Brown recluse spider (Loxosceles) bites cause local tissue destruction through the enzyme sphingomyelinase D, producing a characteristic necrotic ulcer with a violaceous center that develops over days to weeks after the bite. Management is primarily supportive with wound care, tetanus prophylaxis, and monitoring for the rare complication of systemic loxoscelism with hemolysis and renal failure. Deaths from either species are exceedingly rare.

Scorpion stings in the United States are most clinically significant from the bark scorpion (Centruroides sculpturatus), found predominantly in the southwestern states. The venom is neurotoxic and activates sodium channels, causing sustained depolarization of nerve fibers. Symptoms begin with local pain and paresthesias at the sting site, progressing in moderate to severe cases to agitation, roving conjugate eye movements (opsoclonus), muscle fasciculations, excessive salivation, and respiratory distress. Pediatric patients are at highest risk for severe envenomation due to their smaller body mass relative to venom dose. Treatment is supportive for mild cases, with aggressive airway management, benzodiazepines for neuromuscular hyperactivity, and Anascorp (centruroides immune F(ab')2) antivenom administered for severe envenomation.

Marine envenomations present unique challenges due to the diversity of venomous marine organisms and the aquatic environment in which injuries occur. Jellyfish stings, particularly from box jellyfish (Chironex fleckeri) and Portuguese man-of-war, cause intense pain, dermatitis, and in severe cases systemic toxicity including cardiovascular collapse. Treatment involves tentacle removal (using gloves, not bare hands), vinegar application to inactivate undischarged nematocysts (specifically for box jellyfish), and hot water immersion for pain. Stingray envenomation occurs when the barbed tail spine penetrates the skin, injecting a heat-labile protein-based toxin that causes intense pain; treatment centers on hot water immersion at temperatures up to 45 degrees Celsius (113 degrees Fahrenheit) to denature the toxin. Sea urchin injuries involve puncture wounds from brittle spines that may fragment in tissue; treatment involves spine removal and hot water immersion for pain relief.

<image>Panel A: Clinical photographs showing local, large local, and systemic anaphylactic reactions to hymenoptera stings with corresponding treatment algorithms for each severity level. Panel B: Comparison of black widow spider bite presenting with diffuse muscle rigidity and abdominal guarding versus brown recluse spider bite showing a necrotic ulcer with violaceous center and surrounding erythema. Panel C: Bark scorpion photograph with clinical features of severe envenomation including opsoclonus (roving eye movements), and the Anascorp antivenom preparation. Panel D: Marine envenomation treatment guide showing jellyfish tentacle removal with vinegar application, stingray spine wound with hot water immersion setup, and sea urchin spine removal technique.</image>

### Section 8: Electrical Injuries

Electrical injuries are classified by voltage into low-voltage (less than 1,000 volts) and high-voltage (greater than 1,000 volts) categories, each producing distinct patterns of injury. Low-voltage injuries, typically from household current, may still be severe because alternating current at 60 Hz can cause tetanic muscle contraction that prevents the victim from releasing the source, prolonging exposure. High-voltage injuries, encountered in industrial settings and from power lines, cause massive deep tissue destruction that is often far more extensive than surface wounds suggest. Entry and exit wounds may appear relatively small but conceal extensive necrosis of underlying muscle, nerve, and vascular tissue along the current pathway. Arc flash injuries produce thermal burns from the intense heat of an electrical arc without actual current flow through the body, and may cause severe surface burns and ignition of clothing.

Electrical injury affects virtually every organ system in the body. Cardiac effects include arrhythmias ranging from sinus tachycardia to ventricular fibrillation, direct myocardial injury mimicking myocardial infarction, and conduction abnormalities. Neurologic sequelae include loss of consciousness, seizures, peripheral neuropathy, and spinal cord injury from either direct current damage or vertebral compression fractures caused by violent muscle contraction. Musculoskeletal complications include compartment syndrome from muscle edema along current pathways and rhabdomyolysis from massive muscle necrosis. Burns occur at entry and exit sites and may extend deeply into tissue. Delayed complications include cataracts, which may develop weeks to months after injury, and tympanic membrane rupture from the concussive blast effect.

The evaluation of electrical injury begins with a 12-lead electrocardiogram in all patients, which serves as the primary screening tool for cardiac involvement. Patients with abnormal electrocardiograms, cardiac symptoms, loss of consciousness, or high-voltage exposure require continuous cardiac monitoring for a minimum of 24 hours. Laboratory studies include creatine kinase to assess for rhabdomyolysis, troponin for myocardial injury, a basic metabolic panel for electrolyte abnormalities and renal function, and urinalysis for myoglobinuria, which appears as a dark red-brown urine that tests positive for blood on dipstick without red blood cells on microscopy. Imaging studies are obtained as indicated by the clinical presentation and mechanism, including radiographs for fractures from falls or muscle contractions and computed tomography for suspected internal injuries.

Management priorities begin with scene safety, as the electrical source must be confirmed to be de-energized before rescuers approach. Cardiopulmonary resuscitation in electrical injury patients may warrant prolonged efforts because the prognosis for cardiac arrest from electrical injury is better than for other causes of arrest, particularly when ventricular fibrillation is the presenting rhythm. Aggressive intravenous fluid resuscitation targeting urine output greater than 1 milliliter per kilogram per hour is essential to prevent acute tubular necrosis from myoglobin deposition, and sodium bicarbonate alkalinization of the urine may be added to enhance myoglobin clearance. Fasciotomy must be performed promptly for compartment syndrome, which develops from muscle edema within fascial compartments along the current pathway. Admission is indicated for all high-voltage injuries, patients with electrocardiographic abnormalities, cardiac symptoms, or significant burns.

<image>Panel A: Diagram illustrating the differences between low-voltage and high-voltage electrical injuries, including entry and exit wound appearance and the concept of deep tissue injury extending along the current pathway beneath relatively normal-appearing skin. Panel B: Twelve-lead electrocardiogram showing conduction abnormalities and ST-segment changes following high-voltage electrical injury. Panel C: Clinical photographs of entry and exit wounds from high-voltage electrical injury demonstrating the characteristic small, charred entry site and the larger, more destructive exit wound. Panel D: Management algorithm from scene safety through cardiac monitoring, fluid resuscitation targets, rhabdomyolysis treatment, and indications for fasciotomy.</image>

### Section 9: Lightning Injuries

Lightning injuries result from several distinct mechanisms of energy transfer, each producing different patterns and severity of injury. A direct strike, in which lightning contacts the victim directly, carries the highest mortality and is fortunately the least common mechanism. Side splash occurs when lightning strikes a nearby object and the current jumps to the victim, representing one of the most common mechanisms of injury. Ground current is generated when lightning strikes the ground and radiates outward, with the potential difference between the victim's feet driving current through the body. Contact injury occurs when the victim is touching a struck object, and upward streamer injury results from a failed leader channel that generates current from the ground upward but does not connect with the downward lightning channel.

Lightning produces a unique constellation of injury patterns that distinguish it from other electrical injuries. Cardiac effects include asystole, which is common immediately after the strike but from which spontaneous recovery may occur if respiratory function is maintained, and secondary ventricular fibrillation from myocardial hypoxia if respiratory arrest persists untreated. Neurologic effects include transient loss of consciousness, keraunoparalysis (a unique phenomenon of temporary paralysis and sensory loss, typically in the lower extremities, that resolves over hours), and fixed dilated pupils that do not indicate irreversible brain death. Dermatologic findings include Lichtenberg figures, which are pathognomonic fern-like or arborescent patterns on the skin caused by electron showering along the skin surface; these are transient and fade within hours. Tympanic membrane rupture occurs in up to 50 percent of victims from the concussive blast effect, and delayed cataracts may develop weeks to months later.

The management of lightning injuries incorporates the concept of reverse triage, which stands in direct contrast to conventional mass casualty triage principles. In standard triage, pulseless patients are categorized as expectant or dead, and resources are directed to salvageable victims. In lightning mass casualty events, however, pulseless patients should receive the highest priority because they have the greatest potential for successful resuscitation, while those with signs of life will likely survive without immediate intervention. Prolonged cardiopulmonary resuscitation is justified because outcomes following lightning cardiac arrest may be excellent, particularly if respiratory support is provided to prevent secondary hypoxic cardiac arrest. Cervical spine immobilization should be applied given the blast-like mechanism of injury. Fluid resuscitation requirements in lightning injury are typically less aggressive than in other electrical injuries because the brief duration of current flow produces less deep tissue destruction and rhabdomyolysis. Admission is indicated for cardiac involvement, loss of consciousness, and any significant injury.

Prevention of lightning injury is an important public health message that should be reinforced by emergency physicians. The 30-30 rule provides a practical framework: seek shelter when the time between seeing a lightning flash and hearing thunder is less than 30 seconds (indicating the storm is within 6 miles), and remain sheltered for at least 30 minutes after the last observed lightning or thunder. Safe shelter consists of a fully enclosed building with plumbing and electrical wiring (which provide grounding) or a hard-topped motor vehicle with windows closed. Individuals should avoid tall isolated objects, open fields, elevated terrain, bodies of water, and metal objects during thunderstorms. Rubber-soled shoes and tires do not provide meaningful protection against lightning, contrary to popular belief.

<image>Panel A: Illustration of the five mechanisms of lightning injury showing direct strike, side splash from a nearby tree, ground current radiating outward from the strike point, contact injury through a struck object, and upward streamer. Panel B: Photograph of pathognomonic Lichtenberg figures (fern-like patterns) on the trunk of a lightning strike victim. Panel C: Reverse triage algorithm for lightning mass casualty events showing pulseless patients receiving highest priority in contrast to standard mass casualty triage protocols. Panel D: Prevention infographic illustrating the 30-30 rule with safe shelter options and high-risk locations to avoid during thunderstorms.</image>

### Section 10: Diving Emergencies

Barotrauma results from pressure-volume changes in gas-filled spaces as a diver descends or ascends in the water column, governed by Boyle's law (at constant temperature, the volume of a gas is inversely proportional to its pressure). During descent, increasing ambient pressure compresses gas within enclosed body spaces, producing squeeze injuries. Middle ear barotrauma is the most common form, presenting with ear pain, hearing loss, vertigo, and potentially tympanic membrane rupture when the diver fails to equalize pressure through the Eustachian tube. Sinus barotrauma produces facial pain and epistaxis. During ascent, gas expansion within the lungs can cause pulmonary barotrauma, the most dangerous form, which occurs when a diver holds the breath or has trapped gas during ascent. Pulmonary barotrauma may result in pneumothorax, pneumomediastinum, subcutaneous emphysema, or arterial gas embolism.

Decompression sickness results from the formation of nitrogen bubbles in blood and tissues during ascent, when the dissolved nitrogen comes out of solution faster than it can be eliminated through the lungs. Type I (mild) decompression sickness involves musculoskeletal symptoms, classically severe joint pain known as the bends, and pruritic or mottled skin changes (cutis marmorata). Type II (serious) decompression sickness involves the central nervous system with symptoms ranging from paresthesias to paraplegia, the pulmonary system with dyspnea and chest pain known as the chokes, and the vestibular system with vertigo and hearing loss. Risk factors for decompression sickness include rapid ascent, deep or prolonged dives exceeding safe dive tables or computer limits, repetitive dives, dehydration, and exposure to altitude (such as flying) shortly after diving.

Arterial gas embolism is the most immediately life-threatening diving emergency and occurs when air enters the pulmonary venous system through ruptured alveoli during pulmonary barotrauma and subsequently enters the systemic arterial circulation. The onset is characteristically rapid, occurring within 10 to 20 minutes of surfacing, and often immediately upon reaching the surface. The presentation mimics acute stroke with sudden onset of focal neurologic deficits, seizures, loss of consciousness, or cardiac arrest, depending on which vascular territory is affected. The cerebral circulation is most commonly involved due to the upright position of the diver during ascent. Arterial gas embolism is a true medical emergency that requires immediate recognition and treatment.

The definitive treatment for both decompression sickness and arterial gas embolism is hyperbaric oxygen therapy, which works by reducing bubble size according to Boyle's law and by creating a gradient that accelerates nitrogen elimination from tissues. Immediate first aid measures include administration of 100 percent oxygen by non-rebreather mask, which maximizes the nitrogen diffusion gradient and begins bubble resorption. Patients should be positioned supine (the previously recommended Trendelenburg position has been abandoned as it may worsen cerebral edema). Intravenous fluid hydration with isotonic crystalloids helps maintain perfusion and supports nitrogen elimination. Flying and altitude exposure must be strictly avoided until cleared by a diving medicine specialist, as even modest altitude changes can cause bubble expansion and symptom recurrence. The Divers Alert Network (DAN) provides 24-hour consultation and can assist with locating the nearest hyperbaric chamber and arranging patient transfer.

<image>Panel A: Illustration of Boyle's law applied to diving, showing gas volume changes at different depths with corresponding barotrauma patterns during descent (ear and sinus squeeze) and ascent (pulmonary barotrauma, pneumothorax). Panel B: Diagram of nitrogen bubble formation in decompression sickness showing dissolved nitrogen coming out of solution during rapid ascent with bubbles forming in joints (Type I) and spinal cord and brain (Type II). Panel C: CT scan of the head demonstrating intravascular air consistent with arterial gas embolism in a diver who surfaced rapidly. Panel D: Hyperbaric oxygen treatment chamber with treatment protocol diagram showing pressure profiles and oxygen breathing periods for standard treatment tables.</image>

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## Summary

- Heat stroke is defined by core temperature exceeding 104 degrees Fahrenheit with central nervous system dysfunction; rapid cooling by immersion or evaporative methods is the priority, and active cooling should be stopped at 39 degrees Celsius to avoid overcooling
- Hypothermia management requires gentle handling to avoid precipitating arrhythmias; rewarming strategy is matched to severity, and the patient should not be declared dead until warm and dead
- Frostbite is treated with rapid rewarming in water at 37 to 39 degrees Celsius; tissue must never be allowed to refreeze, and surgical debridement is delayed for months until demarcation is established
- Drowning management focuses on hypoxia as the primary problem; all symptomatic patients require hospital observation, and cold water submersion victims may survive prolonged arrest
- Altitude illness treatment centers on descent as the definitive therapy; acetazolamide is used for prevention, nifedipine for HAPE, and dexamethasone for HACE
- Pit viper envenomation causes local tissue destruction and coagulopathy; CroFab antivenom is given for progressive symptoms, and tourniquets, ice, and incision are strictly avoided
- Electrical injury warrants prolonged CPR because outcomes are better than for other causes of arrest; aggressive fluid resuscitation targets urine output above 1 mL/kg/hr to prevent rhabdomyolysis-induced renal failure
- Lightning injury management uses reverse triage, prioritizing pulseless patients because they have the highest potential for successful resuscitation
- Decompression sickness presents with musculoskeletal pain (the bends) or neurologic symptoms and is treated with 100 percent oxygen and hyperbaric oxygen therapy
- Arterial gas embolism presents with stroke-like symptoms within minutes of surfacing and requires emergent hyperbaric oxygen treatment

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## Key Terms

| Term | Definition |
|------|------------|
| Heat stroke | Life-threatening hyperthermia with core temperature exceeding 104 degrees Fahrenheit and central nervous system dysfunction |
| Osborn wave | Pathognomonic J wave on electrocardiogram at the QRS-ST junction in hypothermic patients |
| Frostbite | Tissue freezing injury classified by depth from first-degree (epidermal) through fourth-degree (muscle and bone) |
| Acute mountain sickness | Altitude illness presenting with headache plus nausea, fatigue, dizziness, or sleep disturbance above 2,500 meters |
| HAPE | High altitude pulmonary edema, a noncardiogenic pulmonary edema caused by exaggerated hypoxic pulmonary vasoconstriction |
| HACE | High altitude cerebral edema, vasogenic cerebral edema presenting with ataxia and altered mental status at altitude |
| Decompression sickness | Formation of nitrogen bubbles in blood and tissues during rapid ascent from depth, known as the bends |
| Arterial gas embolism | Entry of air into the systemic arterial circulation through ruptured pulmonary veins during ascent barotrauma |

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