heat hyperpyrexia, a severe and sometimes fatal condition resulting from failure of the temperature-regulating capacity of the body, caused by prolonged exposure to sun or to high temperature. Reduction or cessation of sweating is sometimes an early symptom. Body temperature of 105° F or higher, tachycardia, hot and dry skin, headache, altered mental status, and seizures may occur. Treatment includes cooling, sedation, and fluid replacement. Also called heatstroke, siriasis, sunstroke, thermic fever. Compare heat exhaustion. See also hyperpyrexia.
