[3] Heatstroke is a life-threatening condition due to the potential for multi-organ dysfunction,[6] with typical complications including seizures, rhabdomyolysis, or kidney failure.
[3] Purely exercise-induced heat stroke, though a medical emergency, tends to be self-limiting (the patient stops exercising from cramp or exhaustion) and fewer than 5% of cases are fatal.
Non-exertional heatstroke is a much greater danger: even the healthiest person, if left in a heatstroke-inducing environment without medical attention, will continue to deteriorate to the point of death, and 65% of the most severe cases are fatal even with treatment.
[5] Early symptoms of heat stroke include behavioral changes, confusion, delirium, dizziness, weakness, agitation, combativeness, slurred speech, nausea, and vomiting.
Substances that inhibit cooling and cause dehydration such as alcohol, stimulants, medications, and age-related physiological changes predispose to so-called "classic" or non-exertional heat stroke (NEHS), most often in elderly and infirm individuals in summer situations with insufficient ventilation.
[12] Young children have age specific physiologic differences that make them more susceptible to heat stroke including an increased surface area to mass ratio (leading to increased environmental heat absorption), an underdeveloped thermoregulatory system, a decreased sweating rate and a decreased blood volume to body size ratio (leading to decreased compensatory heat dissipation by redirecting blood to the skin).
[5] Exertional heat stroke (EHS) can happen in young people without health problems or medications – most often in athletes, outdoor laborers, or military personnel engaged in strenuous hot-weather activity or in first responders wearing heavy personal protective equipment.
For humans and other warm-blooded animals, excessive body temperature can disrupt enzymes regulating biochemical reactions that are essential for cellular respiration and the functioning of major organs.
[17] Although its exact mechanism is not yet fully understood, this model theorizes that extreme exercise and heat disrupt the intestinal barrier by making it more permeable and allowing lipopolysaccharides (LPS) from gram-negative bacteria within the gut to move into the circulatory system.
It is diagnosed based on an elevated core body temperature (usually above 40 degrees Celsius), a history of heat exposure or physical exertion, and neurologic dysfunction.
[5] In hot weather, people need to drink plenty of cool liquids and mineral salts to replace fluids lost from sweating.
[5] Immersion in very cold water was once thought to be counterproductive by reducing blood flow to the skin and thereby preventing heat from escaping the body core.
However, research has shown that this mechanism does not play a dominant role in the decrease in core body temperature brought on by cold water.
[citation needed] Dantrolene, a muscle relaxant used to treat other forms of hyperthermia, is not an effective treatment for heat stroke.
[25] Antipyretics such as aspirin and acetaminophen are also not recommended as a means to lower body temperature in the treatment of heat stroke and their use may lead to worsening liver damage.
IV fluid resuscitation is usually needed for circulatory failure and organ dysfunction and is also indicated if rhabdomyolysis is present.
The study also recognized that because of overcrowded conditions in all the participating hospitals during the crisis, the immediate care – which is critical – was not as comprehensive as it should have been.
[26] In rare cases, brain damage has been reported as a permanent sequela of severe heat stroke, most commonly cerebellar atrophy.
[27][28] Various aspects can affect the incidence of heat stroke, including sex, age, geographical location, and occupation.
Heatstroke can affect livestock, especially in hot, humid weather; or if the horse, cow, sheep or other is unfit, overweight, has a dense coat, is overworked, or is left in a horsebox in full sun.