Heat stroke
Temperature above 40 °C with confusion is heat stroke until proven otherwise. Cool first, fast, then look for complications. Paracetamol does not work.
During a heatwave in Karachi, a 60-year-old rickshaw driver is brought in confused and agitated. His skin is hot and dry. Rectal temperature 41.6 °C, pulse 136, BP 94/58, RR 30.
What do you do in the first 30 minutes?
- Start cooling nowDo not wait for bloods, CT or a bed. Every minute above 40 °C damages organs.
- Measure core temperatureRectal if possible. Repeat every 5–10 minutes.
- A B C, oxygen, IV accessSugar, bloods.
- Cool fastCold water immersion if possible, or spray with water and fan, plus ice packs in neck, armpits and groin.
- Stop active cooling at about 39 °CTo avoid overshooting into hypothermia.
- Fluids carefully500 mL to 1 litre, reassess. Smaller amounts in the elderly.
- Look for complicationsKidneys, muscles, clotting, liver, fits.
- Look for other causesInfection, drugs, thyroid storm.
- Temperature 40 °C or more with confusion, fits or coma
- Low BP
- Dark urine or little urine
- Bleeding or bruising
- Not cooling despite treatment
- Infection (meningitis, malaria, sepsis)
- Drug-induced hyperthermia (anticholinergics, stimulants, neuroleptic malignant syndrome)
- Thyroid storm
- Rhabdomyolysis and kidney injury
- Low sugar
| Heat stroke | Core temperature 40 °C or more with confusion, fits or coma, after heat exposure |
| Cooling target | Cool quickly, stop active cooling at about 39 °C |
| Fluids | 500 mL–1 litre, reassess. Smaller in the elderly or heart disease |
| Fits or shivering | Diazepam or lorazepam IV |
| Paracetamol and NSAIDs | Do not work in heat stroke. NSAIDs can harm the kidneys |
Check every dose against a current drug reference and your hospital protocol.
On this page
Heat exhaustion or heat stroke?
- Tired, dizzy, headache, nausea, heavy sweating
- Temperature usually below 40 °C
- Rest in shade, oral fluids and salt, cool down
- Confusion, agitation, fits, coma
- Core temperature usually 40 °C or more
- Skin may be dry or still sweating
- Emergency: cool now
Two types:
- Classic heat stroke: older people, children, those with chronic illness or on certain medicines, during heatwaves, often at home without cooling.
- Exertional heat stroke: young, fit people working or exercising in heat (labourers, soldiers, athletes). Often still sweating.
Cooling
- Remove clothingMove to the coolest place available.
- Best: cold water immersionImmerse the body (not the head) in cold or ice water, if available. Fastest method, especially in exertional heat stroke.
- Otherwise: evaporative coolingSpray lukewarm water on the skin and fan continuously.
- Add ice packsNeck, armpits, groin.
- Cold IV fluidsCan help if available.
- Measure core temperature every 5–10 minutesRectal thermometer or probe.
- Stop active cooling at about 39 °CContinue to monitor. Temperature can rise again.
Paracetamol and NSAIDs do not lower the temperature in heat stroke. The fever is not driven by the brain's thermostat. NSAIDs can also worsen kidney injury and bleeding.
Supportive care
- Airway: intubate if GCS 8 or less or not protecting the airway.
- Low BP: often improves with cooling. Avoid too much fluid in elderly patients.
- Catheter and hourly urine output.
Complications
| Complication | Look for |
|---|---|
| Rhabdomyolysis | Very high CK, dark urine, high potassium |
| Acute kidney injury | Rising creatinine, low urine |
| Liver injury | High ALT and AST (can peak after 24–48 hours) |
| Clotting problems (DIC) | Bleeding, bruising, low platelets, high INR |
| Fits | Treat with benzodiazepines |
| Low sugar, low or high sodium, high potassium | Electrolytes and sugar repeatedly |
| ARDS | Low oxygen |
Investigations
| Test | Why |
|---|---|
| Core temperature | Diagnosis and monitoring |
| Sugar | Low sugar |
| Urea, creatinine, electrolytes, calcium | Kidney injury, potassium |
| CK | Rhabdomyolysis |
| LFTs, clotting, CBC | Liver injury, DIC |
| Blood gas, lactate | Acidosis |
| Urine dipstick | Blood without red cells suggests myoglobin |
| ECG | Arrhythmias, high potassium |
| Blood cultures, malaria test | Infection mimics |
| CT head, LP | If not improving after cooling, or infection suspected |
Mimics
- Meningitis, encephalitis, cerebral malaria, sepsis: fever with confusion. Treat infection if unsure.
- Drugs: anticholinergics, stimulants, serotonin syndrome, neuroleptic malignant syndrome (rigid, on antipsychotics).
- Thyroid storm: goitre, very fast pulse, known thyroid disease.
Prevention during heatwaves
- Drink water regularly, avoid outdoor work in the hottest hours, wear light clothing, rest in shade.
- Check on elderly neighbours, especially those living alone.
- Some medicines increase risk: diuretics, anticholinergics, some antipsychotics.
- Never leave children or the elderly in parked vehicles.
Common mistakes
- Waiting for tests before starting cooling.
- Using oral or axillary temperature to guide cooling.
- Giving paracetamol or diclofenac and waiting.
- Overshooting into hypothermia.
- Pouring litres of fluid into an elderly patient.
- Forgetting to check CK and creatinine.
Frequently asked questions
What is the treatment of heat stroke?
Immediate rapid cooling (cold water immersion if possible, or evaporative cooling with water spray and fans plus ice packs), stopping active cooling at about 39 °C, and supportive care for the airway, fluids, fits and complications.
What is the difference between heat exhaustion and heat stroke?
Heat stroke involves the brain: confusion, fits or coma, usually with a core temperature of 40 °C or more. Heat exhaustion causes tiredness, dizziness and headache without brain involvement.
Does paracetamol help in heat stroke?
No. The high temperature is not caused by the brain's thermostat, so antipyretics do not work.
Test yourself
Exam-style questions on this guide, from our two question banks. Choose an answer to see why each option is right or wrong.
1. A rickshaw driver in a heatwave is confused with a temperature of 41.6 °C. What is the first action?
Answer: Start rapid cooling immediately. Cooling is the life-saving step: cold water immersion if possible, or water spray, fans and ice packs.
- Blood tests then cooling: Delay increases damage.
- Paracetamol IV: Antipyretics don't work in heat stroke.
- Oral fluids and fan: Not enough for heat stroke.
- CT head first: Cool first.
2. During cooling for heat stroke, core temperature is 38.9 °C. What should be done?
Answer: Stop active cooling. Stop active cooling at about 39 °C to avoid overshoot.
- Increase cooling: No.
- Ignore temperature: Must keep monitoring.
- Start paracetamol: No.
- Continue ice packs to 36 °C: Risks hypothermia.
3. On day 2 after heat stroke, a patient has dark urine, CK 45,000 and rising creatinine. What is the problem?
Answer: Rhabdomyolysis. Give IV fluids to keep urine output high, monitor potassium and creatinine.
- Liver failure only: CK points to muscle.
- Sepsis: Not this pattern.
- Haematuria from stones: Not with high CK.
- Normal recovery: No.
4. During a Karachi heatwave, a 60-year-old labourer collapses. Core temperature is 41.5 °C, he is confused and his skin is hot and dry. What is the most important treatment?
Answer: Rapid active cooling. Heat stroke — core temperature above 40 °C with CNS dysfunction — is a medical emergency with high mortality. Cool rapidly: cold-water immersion is most effective; otherwise strip, spray with water and fan, apply ice packs to the neck, axillae and groin. Give IV fluids and monitor for rhabdomyolysis, AKI and DIC. Antipyretics do not work because the hypothalamic set point is normal.
- Oral paracetamol: Antipyretics don’t work in heat stroke.
- IV dantrolene: Dantrolene treats malignant hyperthermia; it does not help heat stroke, which needs rapid cooling.
- Oral fluids and observe: Core temperature 41.5 °C with confusion needs immediate cooling.
5. A 25-year-old labourer working in the sun feels dizzy, weak, nauseated and sweaty. Temperature is 38.6 °C, he is fully alert and BP is 105/70. What is the management?
Answer: Cool, rest, oral fluids and salt. Heat exhaustion: core temperature usually < 40 °C with normal mental state — fatigue, dizziness, headache, nausea, heavy sweating, tachycardia, mild hypotension due to water and salt depletion. Move to a cool place, rest, oral rehydration with electrolytes (IV if vomiting), remove clothing, fan. Any confusion or temperature > 40 °C indicates heat stroke — rapid cooling and hospital care.
- Rapid ice-water immersion and ICU: Ice immersion and ICU are for heat stroke.
- Paracetamol only: Paracetamol is not the main therapy.
- IV dantrolene: Dantrolene is for malignant hyperthermia.
6. During anaesthesia with a volatile agent and suxamethonium, a patient develops muscle rigidity, rising end-tidal CO₂, tachycardia and a high temperature. What is the treatment?
Answer: Stop the trigger and give dantrolene. This is malignant hyperthermia: an inherited (autosomal dominant, usually RYR1) defect in the ryanodine receptor causes uncontrolled calcium release in muscle. Triggers are volatile anaesthetics and suxamethonium. Dantrolene blocks the ryanodine receptor. Hyperkalaemia, acidosis and rhabdomyolysis follow if untreated.
- Switch to propofol, continue, cool: Stopping the trigger is right, but dantrolene is essential; surgery should be finished quickly.
- Give neostigmine to reverse: Neostigmine does not affect the muscle hypermetabolism.
- Paracetamol and surface cooling alone: Fever control alone does not stop the calcium leak in muscle.
- Give IV calcium gluconate: Calcium is not the treatment; the problem is excess calcium release.
7. Why does myoglobin have a hyperbolic oxygen dissociation curve while haemoglobin's is sigmoid?
Answer: Single chain, no cooperativity. Haemoglobin has four subunits; binding of one O₂ increases affinity of the others (cooperativity, T to R state), giving a sigmoid curve suited to loading in lungs and unloading in tissues. Myoglobin is monomeric with high O₂ affinity, so it stores O₂ in muscle and releases it only at very low PO₂.
- Has four haem groups: One haem group.
- Strong 2,3-BPG binding: 2,3-BPG acts on haemoglobin.
- Lower affinity for oxygen: It has higher affinity.
- Iron in the ferric state: Ferric iron (methaemoglobin) cannot bind O₂.
References and dose sources
- WHO fact sheet: Heat and health
- Epstein and Yanovich. Heatstroke (NEJM 2019)
- Ringer's lactate (Hartmann's solution) dosing: Drugs.com: Lactated Ringer's dosage (see also our ringer's lactate (hartmann's solution) dose page)
- Diazepam dosing: Drugs.com: Diazepam dosage (see also our diazepam dose page)
- Dextrose (glucose) dosing: Drugs.com: Dextrose dosage (see also our dextrose (glucose) dose page)
International guidance is linked where it reflects good practice. Where your hospital’s protocol differs, follow your hospital.