Heat stroke is a severe, life-threatening, heat-related illness that involves a core body temperature of more than 40°C (104°F). Cardinal symptoms include neurologic dysfunction and anhidrosis. Patients with heat stroke experience a variety of neurological abnormalities, including ataxia, seizures, headache, mental status changes, confusion, and hallucinations. Individuals most at risk of developing heat stroke are older adults, young children, and psychiatric patients (due to the effects of psychiatric medicines and the possibility of impaired judgement). Additionally, high school athletes are at increased risk of exertional heat stroke.

Heat stroke is caused by the body's inability to fully dissipate heat. It often occurs in the setting of high environmental temperature and heat index, along with physical exertion. A wet-bulb globe temperature index is a comprehensive measure of heat stress on the body, factoring in air temperature, solar radiation, humidity, sun angle, wind speed, and cloud cover. A high wet-bulb globe temperature increases the risk of heat stroke.

Other factors, such as certain medications, medical conditions, and dehydration, may make a person more prone to heat stroke. Medications including beta blockers, calcium channel blockers, selective serotonin reuptake inhibitors (SSRIs), carbamazepine, and valproic acid can increase the risk of heat stroke. Anticholinergic effects of some medications, especially psychiatric medications, can inhibit sweating and thirst.

Children are more prone to heat-related illnesses due to their less-developed sweating mechanisms, a higher metabolic rate that produces more endogenous heat, and a larger body surface area (BSA) to body mass ratio, resulting in faster heat absorption and slower cooling when compared with adults. Additionally, children are less likely to drink fluids in response to dehydration and are less likely to report signs of heat-related illness. Children younger than 2 years have poor thermoregulatory control and must rely on others for hydration. These are all risk factors for heat stroke.

Exertional heat stroke differs from classic heat stroke in its causes and effects. Classic heat stroke can occur in epidemic form in older and younger populations during the right weather conditions. Exertional heat stroke occurs sporadically in mostly young and healthy individuals engaged in strenuous exercise.

Classic heat stroke:

• 20%-30% of patients have hypotension.
• Skin is hot and dry.
• Rhabdomyolysis is mild-to-moderate.
• Renal failure is uncommon.
• Lactic acidosis is mild-to-moderate.
• Patients may be hyperglycemic.
• Disseminated intravascular coagulation is mild-to-moderate.

Exertional heat stroke:

• Skin is hot with profuse sweating.
• Rhabdomyolysis can be severe.
• Renal failure is common.
• Lactic acidosis can be severe.
• Patients may be hypoglycemic.
• Disseminated intravascular coagulation may be severe.

Meningitis, sepsis, neuroleptic malignant syndrome, toxic ingestion, and other conditions may mimic heat stroke, so the diagnosis must be carefully considered based on clinical history. Treatment primarily consists of physical cooling (evaporative, ice water, etc), fluid resuscitation, and monitoring for complications.