Heat-Related Emergencies

Published on 10/02/2015 by admin

Filed under Emergency Medicine

Last modified 22/04/2025

Print this page

This article have been viewed 3072 times

130 Heat-Related Emergencies

Virgil Davis

Key Points

• 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

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

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

Patient Teaching Tips

Heat Illness

The three main types of heat illness are heat cramps, heat exhaustion, and heat stroke.

Heat cramps are painful muscle spasms and a mild form of heat illness that occur when you sweat too much or do not drink enough fluids.

Heat exhaustion is due to dehydration and is more serious.

Heat stroke is marked by severe dehydration and confusion secondary to overheating; it is life-threatening.

Children

Never leave children enclosed in motor vehicles. Yearly, 30 to 40 children die of heat stroke after being left in cars.

Athletics and Strenuous Labor

Drink 500 mL of water or sports drink 2 hours before vigorous exercise or work.

Continue to replace 250 mL of fluid for every 20 minutes of exertion and replace 150% of weight loss with fluid after exertion.

Acclimatization takes at least 2 weeks, and a gradual increase in activity is recommended to safely adjust to hotter environments.

Treatment of Heat Illness

If you have serious heat illness, you may feel lightheaded, nauseated, tired, anxious, and confused.

Get out of the heat into a cool, shaded place or air-conditioned building, and take off some clothing.

Put cold water or cold wet towels on your skin, and drink cold liquids.

If you are confused or lethargic or have a fever, seek medical attention immediately.

Severe Heat-Related Syndromes

Presenting Signs and Symptoms

Heat Exhaustion

Heat exhaustion is a systemic illness that develops as a result of heat stress and depletion of water or salt. Common symptoms are extreme thirst, dizziness, lightheadedness, fatigue, weakness, syncope, headache, malaise, and vomiting. Usually, core body temperature is normal or slightly elevated (but often lower than 40° C). Signs include tachycardia, orthostatic hypotension, tachypnea, and diaphoresis.

All patients with presumed heat exhaustion should undergo neurologic assessment to distinguish heat exhaustion from heat stroke. Heat exhaustion does not cause signs of central nervous system (CNS) dysfunction, such as delirium, ataxia, and seizures.

Heat Stroke

The classic definition of heat stroke was a core body temperature higher than 40° C, CNS dysfunction, and anhydrosis. However, many cases of heat stroke have been reported in which sweating was present and the core temperature was not higher than 40° C. Therefore, the definition has been amended to a form of hyperthermia associated with a systemic inflammatory response leading to a syndrome of multiorgan dysfunction in which encephalopathy predominates.⁸

Heat stroke resulting from failure to stay normothermic in high environmental temperatures is usually termed classic or nonexertional heat stroke, as opposed to exertional heat stroke, in which a significant component of the heat is generated by the body’s muscle tissue through strenuous work or exercise. Although both types of heat stroke are very similar, acute renal failure, rhabdomyolysis, and disseminated intravascular coagulation are more common in patients with exertional heat stroke.

The signs and symptoms of heat stroke are similar to those of heat exhaustion, except for the addition of CNS dysfunction in the form of delirium, hallucinations, ataxia, convulsions, or coma.

Differential Diagnosis and Decision Making

Many other conditions are associated with elevated core body temperature and altered mental status. Box 130.2 contains an extensive list. The EP should regard infection as a strong possibility in patients with these signs. Toxicologic, neurologic (e.g., hemorrhage, seizures), and endocrinologic (e.g., thyroid storm) causes should also be kept in mind and appropriate neuroimaging and laboratory workup ordered. Many cases of heat stroke involve victims with concomitant substance abuse, overdose, or psychiatric illnesses. Evaluation for common overdoses, medication toxicities and substances of abuse should be performed. Additionally, heat stroke often occurs in patients who have significant comorbid conditions, such as cardiac or respiratory diseases, or have another concomitant acute illness, such as infection. Therefore, it is reasonable to assess cardiac function, perform a sepsis evaluation, and evaluate for any additional conditions that the EP suspects.

Tips and Tricks

Both neuroleptic malignant syndrome and heat stroke cause altered mental status and hyperthermia; unlike patients with heat stroke, however, all patients with neuroleptic malignant syndrome also have extrapyramidal rigidity.

Hospital maintenance often has large fans used to dry hospital floors, which can be used to enhance evaporative cooling of a patient with heat illness.

Treatment

Prehospital Management

Morbidity and mortality are correlated with the duration and intensity of elevation in core body temperature. Therefore, field management in which patients with possible heat stroke are identified quickly and cooling measures initiated immediately should have a significant positive effect on outcome. Measures include placing the patient in a cool, shaded environment and removing clothing. Next is either immersion in iced water (immersion) or wetting the skin with water and using a fan to aid evaporation (evaporative cooling).

Continuous monitoring and assessment of core body temperature every 5 to 10 minutes are also recommended. The ability and resources to execute these measures will vary significantly according to the setting (wilderness versus an ironman triathlon medical tent), but even simple measures such as those recommended by the Israeli defense forces—splashing 20 to 40 mL of water on the skin and fanning the person or driving the person in an open car—effectively cool the core body temperature at a rate of 0.14° C/min.⁹

Hospital Management

Some experts liken the treatment of heat stroke to that of trauma, for which there is a “golden hour” for effective intervention and stabilization of the patient. Frequently after this time, aggressive measures cannot overcome the circulatory collapse and organ failure.

The EP’s main goal is to cool the core body temperature to 38.5° C or 39° C as quickly as possible. Active cooling is not continued to normothermic temperatures to avoid the risk of overshooting and causing hypothermia. Usually, significant improvement is noted in the patient’s cardiovascular stability and mental status immediately after cooling. Methods of body cooling are defined in Table 130.3.

Table 130.3 Methods of Core Temperature Cooling

Immersion	Placement of the body into a bath of cold or iced water
Immersion of extremities	Putting only the hands and forearms in iced water
Evaporative cooling	Spraying tepid water or placing a wet sheet on the skin with a fan to facilitate evaporation
Ice packing	Application of ice or cold packs to the groin, axilla, and neck
Invasive measures
Gastric lavage	Lavage with iced water via a nasogastric tube
Peritoneal lavage	Lavage with sterile cold water
Dantrolene, 2-4 mg/kg	Decreases muscle contraction and, in theory, reduces heat production
Benzodiazepines	Theoretically, control shivering and heat production

Debate and research continue about which cooling method is most effective and safest in treating heat stroke. Current research does not definitively answer the question of whether water immersion or evaporative cooling is significantly more effective. However, most evidence indicates that cold water immersion is superior for exertional heat stroke and that the cooler the immersion water bath, the faster the cooling,^5,^10,¹¹ whereas for classic heat stroke both methods are thought to be equally effective. Additionally, if temperature can be reduced within 30 to 60 minutes, the risk for mortality is decreased.¹¹ The choice often depends on which method can be instituted more quickly and effectively. Cold water immersion may be most useful when planned in advance for event medicine and other field applications. Evaporative cooling with the application of ice packs is a practical and effective method that can be instituted with equipment normally available in the emergency department (ED). Ice packs, wet sheets, and a fan will provide rapid cooling. Table 130.4 lists the advantages, disadvantages, and efficacy of various cooling methods.

Table 130.4 Advantages, Disadvantages, and Efficacy of Various Cooling Methods

Shivering and Vasoconstriction

Experts differ about whether shivering and vasoconstriction hinder cooling measures. Some believe that shivering and vasoconstriction require intervention, such as massage or a benzodiazepine, to prevent their negative effects on cooling. Others believe that shivering and vasoconstriction do not significantly slow the rate of cooling and may help prevent hypotension.

Hypotension

Hypotension is a common problem in patients with heat stroke and should be treated aggressively with fluid boluses, which are generally adequate. Central venous pressure of 3 to 8 mm Hg is targeted.⁵ If the patient’s blood pressure remains unresponsive, vasopressors are indicated. One study used isoproterenol (β-adrenergic agonist) to increase peripheral blood flow and cutaneous circulation, but this agent is used infrequently and is unlikely to result in a significant rise in blood pressure.¹² An α-adrenergic agent (e.g., dopamine, which is commonly used) may be more effective in raising blood pressure but has the theoretic disadvantage of causing peripheral vasoconstriction and hence diminishing cutaneous perfusion when given in higher doses.