Clinical Pearls & Morning Reports
Published June 19, 2019
Clinically, heatstroke is characterized by central nervous system dysfunction, multiorgan failure, and extreme hyperthermia (usually >40.5°C). Prompt recognition and treatment of heatstroke in the acute phase may be lifesaving. Read the Review Article here.
Q: How is heatstroke categorized?
A: Depending on its cause, heatstroke may be categorized as either classic (passive) or exertional. Both types derive from failure to dissipate excessive body heat, but their underlying mechanisms differ. Classic heatstroke is due to exposure to environmental heat and poor heat-dissipation mechanisms, whereas exertional heatstroke is associated with physical exercise and results when excessive production of metabolic heat overwhelms physiological heat-loss mechanisms.
Q: How is the diagnosis of heatstroke made?
A: The diagnosis of heatstroke is largely clinical, based primarily on the triad of hyperthermia, neurologic abnormalities, and recent exposure to hot weather (in the classic form) or physical exertion (in the exertional form). Tachycardia, tachypnea, and hypotension are common. Profuse sweating and wet skin are typical of exertional heatstroke, whereas in classic heatstroke, the skin is usually dry, reflecting the characteristic decrease in the sweat-gland response and output in elderly people under heat stress. The skin may be either flushed, reflecting excessive peripheral vasodilatation, or pale, indicating vascular collapse. Extreme hyperthermia during physical exertion does not always indicate heatstroke; many marathon runners finish the race with a high core body temperature but without accompanying changes associated with the clinical picture of heatstroke.
A: For exertional heatstroke, a cooling rate faster than 0.10°C per minute is safe and is desirable for improving the prognosis. Immersion in cold water for the treatment of exertional heatstroke is the accepted method of choice for achieving a cooling rate of 0.20° to 0.35°C per minute, despite numerous reasons, all unfounded, for not using this method. In elderly persons with classic heatstroke, cold-water immersion can yield an acceptable cooling rate, but the treatment of choice involves the use of one or more types of conductive or evaporative cooling, such as infusion of cold fluids (intravascular temperature management); application of ice packs, cold packs, or wet gauze sheets; and fanning. These methods, albeit less efficient than cold-water immersion, are better tolerated by elderly persons and are also readily accessible and easily applied during an epidemic of classic heatstroke, when emergency departments may be inundated with frail elderly patients.
A: No pharmacologic agents accelerate cooling. Antipyretic agents such as aspirin and acetaminophen are ineffective in patients with heatstroke, since fever and hyperthermia raise the core body temperature through different physiological pathways. Furthermore, antipyretic agents aggravate coagulopathy and liver injury in patients with heatstroke. The ryanodine receptor antagonist dantrolene, used in the treatment of malignant hyperthermia, is under investigation for heatstroke therapy but there is currently no evidence to support the claim that this agent is effective for heatstroke. Indeed, the release of skeletal-muscle calcium appears to have no role in the pathophysiology of heatstroke.