Conditions · Emergency medicine and toxicology
Heat stroke and heat exhaustion !
Heat illness ranges from exhaustion to heat stroke, a medical emergency in which body temperature soars and the brain is affected.
Updated 2026-11-01
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In the clinical exam
Why it happens
- Disseminated intravascular coagulation: how consumption causes both clots and bleeding
- Health effects of climate change
- Thermal injury: burns, hyperthermia and hypothermia
- Causes of cell injury
- Heat exhaustion and heat stroke
- Body temperature regulation
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What it is
Heat-related illnesses caused when the body cannot lose enough heat. Heat exhaustion causes weakness and dehydration with normal brain function; heat stroke is a core temperature usually above 40 °C with central nervous system dysfunction and multi-organ injury.
Who gets it
More frequent during heat waves and in hot, humid lowland regions; climate change is increasing exposure in Latin America, including Colombia's Caribbean coast and inter-Andean valleys. Exertional heat stroke affects young athletes, soldiers and outdoor workers; classic heat stroke affects older adults and people with chronic illness during heat waves.
Causes
- Classic (non-exertional): high environmental temperature overwhelming thermoregulation
- Exertional: heat production from intense exercise or labour, often in heat and humidity
- Dehydration and salt loss from sweating (heat exhaustion)
Risk factors
- Extremes of age, obesity, poor fitness and lack of acclimatisation
- Chronic heart, kidney or mental illness and limited mobility
- Medicines and drugs that impair sweating or increase heat (anticholinergics, diuretics, beta-blockers, antipsychotics, stimulants, alcohol)
- Heavy protective clothing or uniforms
- Living alone without cooling, and outdoor work without rest and water
Pathophysiology
When heat gain exceeds loss, the hypothalamic set point is not changed (unlike fever), but cooling fails. High temperature denatures proteins and damages cells; gut ischaemia lets endotoxin enter the blood, triggering a systemic inflammatory response. The result is brain dysfunction, rhabdomyolysis, kidney and liver injury and disseminated intravascular coagulation.
Classification
- Heat cramps and heat syncope
- Heat exhaustion: core temperature below about 40 °C, normal mental status
- Heat stroke: core temperature usually above 40 °C with neurological dysfunction (classic or exertional)
Symptoms and signs
- Heat exhaustion: heavy sweating, thirst, weakness, headache, nausea, dizziness and fainting
- Heat stroke: confusion, abnormal behaviour, ataxia, seizures or coma
- Hot skin, dry in classic heat stroke but often sweaty in exertional
- Tachycardia, fast breathing and hypotension
- Muscle cramps
Diagnosis
- Clinical
- Clinical: heat exposure or exertion, a high core (rectal) temperature and neurological dysfunction. Oral or skin thermometers underestimate core temperature.
- Tests
- Electrolytes, glucose, kidney and liver function, creatine kinase, urinalysis for myoglobin, blood gases, coagulation tests and platelets.
- Imaging
- Head CT when another cause of coma is suspected; chest X-ray if aspiration or pulmonary oedema.
Differential diagnosis
- Sepsis or central nervous system infection
- Neuroleptic malignant syndrome, serotonin syndrome or malignant hyperthermia
- Anticholinergic or stimulant (cocaine, amphetamine) toxicity
- Thyroid storm
- Stroke or status epilepticus
Goal of treatment
Lower core temperature as fast as possible ('cool first, transport second'), support organ function and treat complications.
Treatment
- Acute
- Immediate whole-body cooling: cold-water immersion is fastest for exertional heat stroke; evaporative cooling (water spray and fanning) and ice packs to the neck, armpits and groin are alternatives. Cooling stops at about 38.5–39 °C to avoid overshoot.
- Conservative
- Heat exhaustion: rest in a cool place, remove excess clothing and oral or intravenous rehydration with salt replacement.
- Medical
- Intravenous fluids guided by circulation, benzodiazepines for shivering or seizures. Antipyretics such as paracetamol are not effective because the set point is normal.
- Follow-up
- Continuous core temperature, urine output, electrolytes, kidney and liver function and coagulation; nursing watches for rebound hyperthermia.
Complications
- Rhabdomyolysis and acute kidney injury
- Acute liver injury
- Disseminated intravascular coagulation
- Seizures, cerebral oedema and lasting neurological damage
- Acute respiratory distress syndrome and multi-organ failure
Prognosis
Heat exhaustion recovers fully with treatment. Heat stroke mortality rises with the time spent at high temperature; rapid cooling within the first 30 minutes greatly improves survival, especially in exertional cases.
Prevention
- Gradual acclimatisation, scheduled rest and water for outdoor work and sport
- Avoiding heavy exertion in the hottest hours
- Checking on older and isolated people during heat waves and providing cool places
Test yourself
Think of the answer, then tap the question to see it.
What two features define heat stroke?
High core temperature (usually above 40 °C) and central nervous system dysfunction (confusion, seizures, coma).
What is the most effective cooling method for exertional heat stroke?
Cold-water immersion, started on site as quickly as possible.
Why are antipyretics not useful in heat stroke?
The hypothalamic set point is normal; the problem is failure of heat loss, not a raised set point as in fever.
Which laboratory complications should be monitored in heat stroke?
Rhabdomyolysis (creatine kinase), acute kidney injury, liver injury and disseminated intravascular coagulation.
Related conditions
- Rhabdomyolysis
- Acute kidney injury
- Disseminated intravascular coagulation
- Dehydration (fluid volume deficit)
- Malignant hyperthermia
- Neuroleptic malignant syndrome
- Serotonin syndrome
- Anticholinergic toxicity (incl. scopolamine «burundanga»)
- Sepsis and septic shock
- Thyroid storm
- Acute liver failure
- Cocaine and sympathomimetic toxicity
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Heat emergencies (MedlinePlus, US National Library of Medicine, 2026).
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