Heat-Related Emergencies

130 Heat-Related Emergencies

• Heat stroke is a life-threatening hyperthermic syndrome characterized by central nervous system dysfunction and associated multisystem organ failure.

• The main goal of therapy is rapid reduction of the patient’s core temperature to about 39° C with one of two methods—evaporative cooling or cold water immersion.

Perspective

Heat-related injury spans a wide spectrum from the unpleasant and transient conditions of heat cramps or prickly heat to the life-threatening multisystem organ failure of heat stroke. The most important risk factors for heat illness are listed in Box 130.1. Mechanisms of acclimatization are listed in Table 130.1.

Box 130.1 Risk Factors for Severe Heat Illness

Extremes of age (children and people 65 and older)

Alcohol and drug intoxication

Impaired cardiac function

• Illness (e.g., heart failure)

• Drug therapy (e.g., beta-blockers)

Anhydrosis from the use of anticholinergic agents or phenothiazines

Intercurrent illness

Psychiatric Illness

Lack of air conditioning

Lower socioeconomic status.

Table 130.1 Acclimatization Mechanisms

Cardiac	Increased cardiac performance: higher cardiac output
Vascular	Increases in: Plasma volume Renal flow Shunting of blood away from the visceral circulation
Endocrine	An enhanced renin-angiotensin-aldosterone system and improved salt retention by the kidneys and sweat glands result in better fluid retention
Renal	Increased glomerular filtration rate
Sweat glands	The increased volume of sweat produced and the more dilute sweat reduce salt loss and indirectly diminish dehydration
Muscle	Improved ability to resist rhabdomyolysis from exertion
Cellular	Upregulated transcription of heat shock proteins

Epidemiology

Roughly 688 people die yearly of heat-related causes, Arizona has the highest incidence at 1.7 per 100,000, followed by Nevada (0.8 per 100,000) and Missouri (0.6 per 100,000).¹ An estimated half of the deaths are weather related, and 5% result from being enclosed in motor vehicles, boiler rooms, or kitchens; in the remaining cases, the causes are unspecified.² Mortality from heat stroke with appropriate treatment is reported to be between 0% and 28%.³^–⁵

Pathophysiology of Heat Stroke

Severe heat illness is thought to result from three main mechanisms: physiologic alterations in response to hyperthermia, direct cytotoxic effects of heat, and inflammatory and coagulation responses of the host, which interact to create a spiraling deterioration resulting in circulatory collapse and multisystem organ failure.

Failure of thermoregulation occurs when fluid and electrolyte replacement is inadequate; it results in diminished cardiac output, hypotension and acute renal failure, and shunting of blood away from the splanchnic circulation, which leads to intestinal ischemia. Increased gut permeability and the entrance of endotoxins stimulate additional inflammatory mediators.

Heat itself has a direct cytotoxic effect and causes cell death over a period of 45 minutes to 8 hours at body temperatures of 41.6° C to 42° C ⁶; below these temperatures, cell death can still occur through apoptosis.⁷

Heat induces higher production of numerous inflammatory cytokines that contribute to the neuronal injury and hypotension seen in patients with heat stroke, and it results in coagulation and endothelial cell injury, which can lead to disseminated intravascular coagulation and greater vascular permeability.

Figure 130.1 diagrams the current understanding of the pathophysiology of heat stroke.

Fig. 130.1 Algorithm of the pathophysiology of heat stroke.

Minor Heat-Related Syndromes

Presenting Signs and Symptoms

As stated earlier, heat-related illness is a continuum. Table 130.2 summarizes the various types of heat illness.

Table 130.2 Heat-Related Illnesses and Treatment

DIAGNOSIS	KEY FEATURES	TREatMENT
Mild
Heat edema	Mild edema of the hands and feet as a result of interstitial edema	Elevation, compression Self limited Diuretics not indicated
Prickly heat	Erythematous, maculopapular rash	Antihistamines Antibiotics effective against staphylococci if secondary cellulitis present
Heat cramps	Severe muscle spasms during or after vigorous exercise	Intravenous or oral rehydration
Severe
Heat exhaustion	Dehydration, weakness, fatigue Normal or mildly elevated temperature (<40° C) Normal mental status	Remove clothing Remove from heat Intravenous or oral fluids Check electrolytes and creatinine Generally discharge Drink fluids and rest for 1-2 days
Heat stroke	Abnormal mental status Multisystem organ failure Hyperthermia Often temperature >40° C Often anhydrosis	Rapid cooling with immersion or evaporative methods to core temperature <39° C Supportive care Hospital admission

Heat Edema

Heat edema is a self-limited illness characterized by mild swelling of the hands and feet as a result of increased interstitial fluid after heat exposure.

Prickly Heat

Clogging of the sweat glands leads to an erythematous, maculopapular, and pruritic rash commonly called prickly heat.

Heat Syncope

Heat syncope results from heat-induced volume depletion and peripheral vasodilation, which often occur in people with decreased vasomotor tone, such as the elderly, and in people poorly acclimated to the heat. It is important to regard heat syncope as a diagnosis of exclusion and to evaluate for other plausible causes of syncope. In addition, the emergency physician (EP) should remember to evaluate for any injuries sustained during a fall as a result of syncope. The patient should have a rapid response to hydration. Electrolytes should be evaluated in patients with signs of volume depletion.

Heat Cramps

Heat cramps are involuntary muscle spasms, most commonly of the calves, thighs, or shoulders, that occur either during or after vigorous physical activity. Cellular hyponatremia and hypokalemia are thought to cause this problem. Rhabdomyolysis is a very rare complication that can result from prolonged muscle spasm.

Treatment

Most minor heat-related syndromes are mild and require simple or no treatment. Treatment is summarized in Table 130.2 for these conditions.

Follow-up, Next Steps in Care, and Patient Education

Minor heat-related illnesses rarely require admission. Patients with heat syncope and significant electrolyte abnormalities should be admitted for correction. Patients with heat cramps who show evidence of impending rhabdomyolysis require hospital admission for aggressive hydration and monitoring of renal function. Informing patients about how to avoid severe heat illness when they have mild heat illness may prevent future recurrence or more serious injury. The Patient Teaching Tips box lists information that can be given in the form of an educational handout to patients with heat illness.

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Tags: Emergency Medicine Clinical Essentials

Jun 14, 2016 | Posted by admin in EMERGENCY MEDICINE | Comments Off

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