Heat-related illnesses comprise a continuum of disorders ranging from the minor heat edema, heat rash, heat cramps, and heat exhaustion to the more life-threatening condition known as heat stroke. As a general rule, it is involves a process whereby heat gain overwhelms the body’s mechanisms of heat loss. Often it is caused by an impairment of the body’s cooling and adaptive mechanism to effectively transfer heat to the environment, thus leading to a rise in core temperature. 1

Risk Factors 1,2

Extremes of age (<4 years and >75 years)

Strenuous exercise

Ambient temperature

Cardiovascular disease

Dehydration

Obesity

Psychiatric illnesses

Medications

Although mostly preventable, heat stroke has a mortality rate of 10-20% even with treatment.3 Therefore, it is essential for its early recognition and intervention. This post will outline how to effectively approach and handle heat stroke in the emergency department.

What is Heat Stroke 1–3

Core body temperature ≥40ºC (104ºF) with associated altered mental status

Two types:

Classic Heat Stroke (non-exertional) Interference with thermoregulation or cooling strategies

Typically occurs over days

Examples: extremes of age, poverty, heat wave, lack of air conditioning, immobility, confined spaces (cars, attics, boiler rooms), cardiovascular disease, obesity, anhidrosis, physical disability, psychiatric conditions, medications, alcoholism, or recreational drugs Exertional Heat Stroke Typically occurs within minutes to hours

Occurs in otherwise healthy individuals who perform heavy exercise in high temperature settings, such as young athletes, military recruits, and fire/police trainees

Distinctions between heat stroke and heat exhaustion 3

Heat Exhaustion Heat Stroke Temperature <40C (104F) ≥40C (104F) Mental Status Normal mental status

Brief period of mild confusion

Brief syncope Altered mental status – hallmark of heat stroke (confusion, poor attention, poor memory, agitation, delirium, confusion, hallucinations, coma, seizures) Airway & Breathing Clear airway

May be tachypneic Airway may be compromised

Tachypneic Circulation Tachycardic

Normal BP

Mild-moderate dehydration Tachycardic

Hypotension/ wide pulse pressure

Moderate-severe dehydration Skin Sweating Dry skin (classic heat stroke)

Sweating (exertional heat stroke) Other Nausea/vomiting

Headache

Generalized fatigue

Weakness

Hypo/hypernatremia Nausea/vomiting

Diarrhea

DIC

Rhabdomyolysis

Renal failure

Cardiogenic shock

Liver failure

Differential Diagnosis for Hyperthermia 4

Environmental Heat-related illnesses

Drugs and medications Malignant hyperthermia Alcohol withdrawal Salicylate toxicity Neuroleptic malignant syndrome Stimulant toxicity (cocaine, phencyclidine, amphetamine) Anti-cholinergic toxicity

Infectious

Neurologic Hypothalamic stroke Status epilepticus Cerebral hemorrhage

Endocrine Thyroid storm Pheochromocytoma

Oncologic Lymphoma Leukemia



Diagnostic Workup 1–3

Core temperature with frequent monitoring Rectal temperature is the most reliable assessment of core temperature 1 – level C evidence (based on consensus, disease-oriented evidence, usual practice, expert opinion, or case series) Laboratory studies Compete blood count (CBC)

Electrolytes

Arterial or venous blood gas

Glucose

Blood urea nitrogen (BUN)/creatinine

Creatinine kinase (CK)

Liver enzymes

Coagulation studies

Urinalysis

Urine myoglobin Electrocardiogram (ECG), if history of syncope or cardiovascular disease Chest radiograph to rule out aspiration or pulmonary infection Consider for CT brain ± lumbar puncture, based on clinical suspicion

Treatment and Disposition 2

Basic supportive measures Airway protection

Cardiac monitoring

IV fluid therapy with normal saline or lactated Ringer solution Goal: maintain mean arterial pressure >60 mmHg Correct electrolyte abnormalities

Rapid cooling Target temperature: A range of target temperatures have been recommended at 37-40.1ºC. 5 Often 39-40ºC is recommended to avoid overshoot hypothermia.

Rapid accessibility to cooling is the most effective method to prevent heat-related mortality 4

Although the literature is sparse on the ideal cooling method for EXERTIONAL heat stroke, consider cold water immersion — associated with lowest morbidity and mortality 1 (Level C evidence)

— associated with lowest morbidity and mortality (Level C evidence) Evaporative cooling with mist and fan is also effective Avoid ice water as shivering may induce thermogenesis Other cooling methods: ice pack cooling to groin and axilla, cooling blanket, thoracic/peritoneal lavage Do not use antipyretics!

with mist and fan is also effective Pharmacotherapy Manage seizures and severe shivering with short acting benzodiazepine

Treat rhabdomyolysis IV fluid resuscitation and sodium bicarbonate (3 ampules of 50 mL of 8.4% bicarbonate in 1 L 5% D5W at 250 mL/hr) Consider furosemide if inadequate urine output. Consider antibiotics IF and ONLY IF infection is high on list of possible etiologies.

Complications/Disposition Major complications: rhabdomyolysis, liver failure, renal failure, heart failure, cardiovascular collapse, pulmonary edema, or disseminated intravascular coagulation (DIC)

rhabdomyolysis, liver failure, renal failure, heart failure, cardiovascular collapse, pulmonary edema, or disseminated intravascular coagulation (DIC) Admit to the intensive care unit for further observation

Take Home Messages About Heat Stroke

Heat stroke is a medical emergency that requires prompt recognition and treatment.

It is characterized by altered mentation and hyperpyrexia as a result of thermoregulatory dysfunction, leading to multi-organ failure and tissue damage.

Treatment includes stabilization of ABCs, rapid cooling, managing fluid and electrolyte imbalances, and treating secondary complications.

Important: Antipyretics are NOT effective in reducing core body temperature in heat stroke! Use cold water immersion, evaporative methods, or other cooling methods along with benzodiazepines to reduce shivering when necessary.

Image: (c) Can Stock Photo

1. PubMed] Becker J, Stewart L. Heat-related illness. Am Fam Physician. 2011;83(11):1325-1330. 2. Tran TP. Heat emergencies. In: Ma OJ, Cline DM, ed. Emergency medicine manual. 6th ed. McGraw-Hill, NY: 2004:564-565. 3. PubMed] Glazer J. Management of heatstroke and heat exhaustion. Am Fam Physician. 2005;71(11):2133-2140. 4. PubMed] American C, Armstrong L, Casa D, et al. American College of Sports Medicine position stand. Exertional heat illness during training and competition. Med Sci Sports Exerc. 2007;39(3):556-572. 5. PubMed] Bouchama A, Dehbi M, Chaves-Carballo E. Cooling and hemodynamic management in heatstroke: practical recommendations. Crit Care. 2007;11(3):R54.