Hyperthermia & Heat Stroke: Heat-Related Conditions
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Hyperthermia & Heat Stroke: Heat-Related Conditions Joseph Rampulla, MS, APRN,BC eat-related conditions occur when excess heat taxes or overwhelms the body’s thermoregulatory mechanisms. Heat illness is preventable and occurs more Hcommonly than most clinicians realize. Heat illness most seriously affects the poor, urban-dwellers, young children, those with chronic physical and mental illnesses, substance abusers, the elderly, and people who engage in excessive physical The exposure to activity under harsh conditions. While considerable overlap occurs, the important the heat and the concrete during the syndromes are: heat stroke, heat exhaustion, and heat cramps. Heat stroke is a life- hot summer months places many rough threatening emergency and occurs when the loss of thermoregulatory control results sleepers at great risk in hyperpyrexia (very high fever) and severe damage to many internal organs. for heat stroke and hyperthermia. Photo by Epidemiology Sharon Morrison RN Heat illness is generally underreported, and the deaths than all other natural disasters combined in true incidence is unknown. Death rates from other the USA. The elderly, the very poor, and socially causes (e.g. cardiovascular, respiratory) increase isolated individuals are disproportionately affected during heat waves but are generally not reflected in by heat waves. For example, death records during the morbidity and mortality statistics related to heat heat waves invariably include many elders who died illness. Nonetheless, heat waves account for more alone in hot apartments. Age 65 years, chronic The Health Care of Homeless Persons - Part II - Hyperthermia and Heat Stroke 199 illness, and residence in a poor neighborhood are greater than 65. In addition, children absorb more all associated with higher risk of death during heat heat relative to their body mass and do not sweat as waves. much as adults, thereby rendering them particularly From 1979 through 1999, 8015 deaths in the vulnerable to heat disorders. Asphalt and concrete USA were directly attributed to excessive environ- in cities absorb and retain heat, creating the mental heat exposure. During the 7-day Chicago “urban heat phenomenon” which also interferes heat wave of 1995, the death rate increased by 85%, with nighttime cooling in cities. Numerous drugs with the majority of deaths among the poor and affect heat dissipation and heat production, most socially isolated. Interestingly, northern cities have notably anticholinergics, beta-blockers, antipsy- greater increases in death rates during hot weather chotics, tricyclic antidepressants, lithium, ethanol, than southern cities. Northern cities have wider and diuretics. Stimulants also generate excess heat: swings in temperature, fewer air conditioners, and cocaine, amphetamines, MDMA (Ecstasy), and the citizens are not as well acclimated to the heat. supra-therapeutic doses of thyroxine (see Table 2). Thermoregulation Heat Stroke Metabolism, muscle activity, and the environ- Heat stroke is a life-threatening febrile illness mental temperature all contribute to the generation due to the breakdown of the body’s heat control and maintenance of body heat. When the body systems and the subsequent acute immunologic and temperature rises, peripheral vessels dilate and metabolic reactions to elevated body temperatures. cardiac output increases, shunting blood flow closer When simple exposure to high environmental to the surface of the skin where it can be cooled. temperature overwhelms thermoregulatory Sweating provides water on the skin’s surface, which mechanisms, the condition is called “classic” or non- then evaporates and further cools the body. This exertional heat stroke. When the body temperature cooling process by evaporation depends on the rises in a healthy person who exercises strenuously in gradient between the body temperature and the a hot environment, this is referred to as “exertional atmospheric temperature. Humidity and high heat stroke.” environmental temperatures hinder heat dissipa- Risk factors may be present but are not requi- tion. Behavioral factors play an important role in site. The onset of heat stroke is rapid, and patients cooling, including seeking a cooler environment or may have a prodrome of weakness, headache, chills, shade from the sun, reducing physical activity, and ataxia, and nausea. Chest pain may be present, as replacing the water and salt lost through sweating. well as shortness of breath and abdominal pain. People with impaired mobility or impaired judg- Thirst is not a reliable indicator of impending heat ment may not be able to engage in these behaviors, stroke. The body temperature rises rapidly, sweating and are at risk for heat illness. ceases, and multiple system failure ensues (usually After 7-14 days of persistent heat exposure, the heralded by neurological problems). An acute phase body becomes acclimated and adjusts to the heat inflammatory reaction appears to be involved in the through increased sweating, avid retention of salt progression from heat exhaustion to heat stroke. by the kidneys, and an increase in cardiac stroke During heat stroke fever is 104°F (40°C) volume. Even with adequate water and salt intake, or greater. Sweating usually ceases and the skin homeostatic mechanisms may break down and becomes hot and dry. Confusion, delirium, and cause severe hyponatremia and cerebral edema. ataxia are followed by loss of consciousness. Some patients will have seizures that usually occur during Heat Disorders cooling. Tachycardia and hyperventilation are When the body’s ability to dissipate heat is over- common vital sign changes. Laboratory examina- whelmed and/or too much water and salt are lost, tion reveals an elevated hematocrit (secondary to the core body temperature rises and several distinct hemoconcentration), electrolyte and acid-base heat syndromes may develop (see Table 1). Many disturbances (typically hyponatremia, metabolic risk factors can increase a person’s susceptibility for acidosis, and hypokalemia), and evidence of muscle, developing a heat syndrome, including: general- renal, and hepatic damage. The electrocardiogram ized skin conditions (e.g. sunburn, psoriasis) that and cardiac enzymes may indicate myocardial injury. interfere with sweating; dehydration; alcoholism; Thrombocytopenia can be profound if disseminated mental illness; cardiopulmonary disease; and age intravascular coagulation has occurred. 200 The Health Care of Homeless Persons - Part II - Hyperthermia and Heat Stroke The Health Care of Homeless Persons - Part II - Hyperthermia and Heat Stroke 201 Table 1: Major Heat Syndromes Disorder Mechanism Clinical Treatment Comments Heat Stroke Classic: Inability to Failure of Often rapid onset Support airway, Highly lethal compensate for hot thermoregulatory breathing, & circulation environment. Occurs systems resulting in May be preceded by 20% or more have in patients with severe hyperthermia headache, nausea, Patient must residual neurological impaired homeostatic and multi-system weakness, and immediately be damage mechanisms damage myalgias moved to a cooler environment and Patients with Exertional: Failure Usually accompanied High fever 105°-107°F transported to the exertional heatstroke to dissipate the by electrolyte (40.6°C - 46.7°C) hospital may continue to sweat heat generated by imbalance and cardiac strenuous exercise. arrythmias. Often Dilated pupils Hospital treatment Occurs in otherwise seizures, neurological consists of healthy persons who damage, DIC, Hot dry skin aggressive cooling, overexert under heat rhabdomyolysis, renal fluid and electrolyte stress conditions and hepatic failure Lack of sweating replacement, and (classic) support of vital functions Confusion, ataxia and/ or loss consciousness Fast thready pulse Hypotension Heart failure Heat Exhaustion Fluid and electrolyte Water and/or salt Insidious or sudden Patient should lie May be similar in imbalance due to depletion from onset down in a cool area presentation to insulin sweating resulting in excessive sweating shock, alcohol/drug hypovolemia that is inadequately Weakness, Fluid and salt should abuse/withdrawal, replaced lightheadedness, be replenished. or hypovolemia from syncope, sweating, Slightly salty or sports occult blood loss Hypovolemia causes nausea drinks can be given in weakness and sips over 2-4 hours. Usually benign, but collapse Low-grade fever IV’s needed if very ill may progress to heat or unable to take oral stroke Pale, cool, clammy fluids skin Sweating Thready pulse Low BP May be ataxic and confused Therapy includes immediate cooling, support Heat Exhaustion of failing organ systems, and repletion of fluids Heat exhaustion is profound weakness caused with correction of electrolyte abnormalities. Time by the loss of water and salt due to sweating during is critical, and patients should be immediately trans- heat exposure. The manifestations of heat exhaus- ported to a hospital. If possible, remove the patient tion can be similar to several other conditions, from the hot environment while awaiting the including insulin shock, hyperthyroidism, toxic ambulance. Once airway, breathing, and circulation ingestions, alcohol withdrawal, arrhythmias, and are secure, cooling should begin as soon as possible. hypovolemia from bleeding or diarrhea. The major This includes removal of clothing, applying water signs and symptoms of heat exhaustion are thirst, and ice to the skin, and fanning. The initial target malaise, headaches, myalgias, shortness of breath, temperature