Heat Stroke

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Chapter 77 Heat Stroke

William J. Benedetto, MD

1 What is heat stroke?

Heat stroke is a life-threatening illness characterized by a core body temperature above 40° C and central nervous system (CNS) dysfunction. The CNS abnormalities may include delirium, lethargy, convulsions, or coma. Anhidrosis (lack of sweating) may or may not be present, depending on the type and presentation of the illness.

2 What is the pathophysiology of heat stroke?

The body gains heat from metabolism and from the environment, and this heat must be dissipated to maintain a normal temperature of 37° C. This process (thermoregulation) relies primarily on cutaneous vasodilatation and evaporation of sweat. When these processes are overwhelmed, core temperature will rise. When the core temperature exceeds 40° C, an acute phase response is elicited from heat-stressed cells including cytokines and heat shock proteins.

3 What are the two types of heat stroke? How do they present?

image Classic heat stroke is associated with high environmental heat and humidity with inadequate cooling. There is generally no history of significant exercise or exertion. Classic heat stroke typically has a slow onset, often developing over days. It generally afflicts the elderly and the chronically ill, who may present with anorexia, nausea, vomiting, headache, dizziness, confusion, and hypotension. Anhidrosis is a common finding. Up to 25% of patients present with hypotension.

image Exertional heat stroke usually affects young people in good health who are exercising in a hot, humid environment, often with clothing or equipment that restricts cooling. It is rapid in onset, and nausea, dizziness, and confusion are common. Fatigue, ataxia, coma, and nuchal rigidity or posturing may also occur. Profuse sweating is a typical finding on examination.

4 Which populations are at greater risk for heat stroke?

image Extremes of age—because of relatively poor temperature regulation in the young and old, especially during heat waves

image Chronically ill—especially those taking drugs that predispose to heat illness

image Military recruits—especially Northerners not acclimated to the weather in the Southern region of the United States

image Athletes—most commonly football players and runners

image Laborers—especially if water losses have not been replaced

image Obese individuals—because heat dissipation is compromised

5 Which medications predispose a person to heat stroke?

image Drugs increasing heat production through increased motor activity: cocaine, amphetamines, ephedrine, phencyclidine, lysergic acid diethylamide, alcohol withdrawal

image Drugs decreasing thirst: for example, haloperidol

image Drugs decreasing sweating: antihistamines, anticholinergics, phenothiazines, β-blockers

6 What is the mortality rate of heat stroke?

When treatment is prompt and effectively lowers core temperature, mortality in young, healthy patients is minimal. In the setting of delayed effective treatment and significant comorbidities, mortality can be as high as 70%.

7 What are the common sequelae and complications of heat stroke?

Heat stroke can lead to multiorgan dysfunction syndrome including the following:

image Encephalopathy

image Renal failure or rhabdomyolysis (most commonly in exertional heat stroke)

image Acute respiratory distress syndrome

image Myocardial injury and circulatory collapse

image Hepatocellular injury

image Intestinal ischemia and infarction

image Pancreatic injury

image Hemorrhagic complications and disseminated intravascular coagulation, which are common complications and important mechanisms in heat stroke morbidity and mortality

8 Which other diagnoses should be considered in a patient presenting with hyperthermia?

image Other hyperthermic syndromes

image Malignant hyperthermia
image Neuroleptic malignant syndrome
image Drug-induced hyperthermia

image Infections

image Especially meningitis, encephalitis, and sepsis

image Endocrinopathies

image Such as thyroid storm and pheochromocytoma

image CNS lesions

image Hypothalamic bleeding, acute hydrocephalus

9 How can heat stroke be prevented?

Heat stroke is currently more preventable than treatable. Efforts to prevent heat stroke should focus on acclimatization (gradual exposure to higher temperature environments and increasing work loads), rescheduling activities to cooler times of day, increasing consumption of nonalcoholic fluids, and removing vulnerable populations from high-heat areas.

10 What is the most important aspect in the treatment of heat stroke?

Rapid cooling is the main therapeutic goal for treatment of heat stroke. Mortality increases dramatically with even relatively short delays in cooling. Delay in cooling is a better predictor of poor patient outcome than the degree of hyperthermia.

11 What treatment modalities are effective for rapid cooling?

Immersion in ice water is effective though can be difficult to do and is often poorly tolerated. This modality may not be appropriate in the comatose or combative patient. Aggressive evaporative cooling, consisting of treatment with tepid water spray (40° C [104° F]) and a forced air stream from a fan, has proved successful and is an easy therapy to apply. Ice packs and massage may be used. Techniques such as iced gastric lavage and peritoneal lavage have also been reported. Though a cooling target has not been clearly established, a core temperature of 39° C or less is considered safe.

12 In addition to cooling, what other treatment is appropriate?

Heat stroke can lead to multiorgan dysfunction, and supportive therapy is indicated, as appropriate:

image Airway protection and mechanical ventilation

image Seizure control with benzodiazepines

image Monitoring of circulatory status and fluid therapy or pressors as needed

image Volume expansion and renal monitoring in the setting of rhabdomyolysis

image Correction of electrolyte abnormalities

13 Which laboratory abnormalities are seen in heat stroke?

image Acid/base disturbance.

image Classic heat stroke commonly presents with a respiratory alkalosis.
image Exertional heat stroke presents with a respiratory alkalosis and lactic acidosis.

image Hypophosphatemia is common in classic heat stroke, though heat stroke associated with exertion may present with hyperphosphatemia from rhabdomyolysis.

image Hypokalemia is common except in the setting of rhabdomyolysis.

image Serum proteins and hypercalcemia increase because of volume contraction.

14 What prognostic signs predict outcome?

Longer duration of hyperthermia is associated with poorer outcome. Coma, hypotension, hyperkalemia, and an aspartate aminotransferase level > 1000 units are associated with a poor prognosis.

15 What steps can be taken to prevent heat stroke?

image Maintain adequate fluid intake during periods of high temperature, high humidity, or increased activity levels.

image Decrease levels of activity during time of high heat and humidity.

image Control ambient temperature and humidity if possible.

image Dress appropriately for the weather.

image Use prudence during acclimation to a hotter environment.

image Adjust dosages of predisposing drugs, if possible, during hot weather.

image Be aware of symptoms of impending heat stroke.

16 What other medications have been considered for treatment of heat stroke?

image Activated protein C has been shown to be useful treatment for heat stroke in a rodent model and has generated some interest in the critical care community, though currently no human trials have been published.

image Dantrolene has been investigated for treatment of heat stroke, and a nonrandomized trial demonstrated some efficacy. However, a randomized and blinded trial did not confirm this result, and dantrolene is not indicated for the treatment of heat stroke.

Key Points Diagnostic Criteria for Heat Strokeimage

1. Exposure to increased heat stress: exercise and/or increased temperature and humidity.

2. Altered mental status.

3. Core (rectal) temperature greater than 40° C.

4. Sweating may or may not be present.

Bibliography

1 Bouchama A., Dehbi M., Chaves-Carballo E. Cooling and hemodynamic management in heatstroke: practical recommendations. Crit Care. 2007;11:R54.

2 Bouchama A., De Vol E.B. Acid–base alterations in heat stroke. Intensive Care Med. 2002;27:680–685.

3 Bouchama A., Knochel J. Heat stroke. N Engl J Med. 2002;346:1978–1988.

4 Curley F.J., Irwin R.S. Disorders of temperature control part II: hyperthermia. In: RS Irwin, JM Rippe. Intensive Care Medicine. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2003:762–777.

5 Leon L., Helwig B. Heat stroke: role of the systemic inflammatory response. J Appl Physiol. 2010;109:1980–1988.

6 Marini J.J., Wheeler A.P. Thermal disorders. In Critical Care Medicine, The Essentials. Philadelphia: Lippincott Williams & Wilkins; 2006. pp 466–476

7 O’Connor F., Casa D., Bergeron M., et al. American College of Sports Medicine Roundtable on Exertional Heat Stroke—Return to Duty/Return to Play: Conference Proceedings. Curr Sports Med Rep. 2010;9:314–321.

8 Xiao-Jing L., Yi-Lei L., Gui-Ping M., et al. Activated protein C can be used as a prophylactic as well as a therapeutic agent for heat stroke in rodents. Shock. 2009;32:524–529.

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