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Hyperthermia and hypothermia

Background knowledge ๐Ÿง 


  • Hyperthermia: elevated body temperature due to failed thermoregulation.
  • Hypothermia: lowered body temperature below 35ยฐC due to excessive heat loss or inadequate heat production.
  • Both conditions are medical emergencies requiring prompt treatment.
  • Differentiate from fever, which is a regulated rise in body temperature due to infection or inflammation.


  • Hyperthermia: common in hot climates and during heatwaves; affects elderly, athletes, and those with underlying health conditions.
  • Hypothermia: common in cold climates; affects homeless individuals, elderly, and those exposed to cold water or weather.
  • Both conditions can occur in the UK, particularly in vulnerable populations.
  • Mortality is higher in extremes of age and those with comorbidities.

Aetiology and Pathophysiology

  • Hyperthermia: excessive heat production (e.g., exercise), impaired heat dissipation (e.g., high humidity), drugs (e.g., anticholinergics, amphetamines).
  • Hypothermia: prolonged exposure to cold, impaired thermoregulation (e.g., hypothyroidism, sepsis), alcohol and drug intoxication.
  • Hyperthermia results in protein denaturation, enzyme dysfunction, and cellular damage.
  • Hypothermia leads to slowed metabolism, impaired cardiac and CNS function, and eventual multi-organ failure.
  • Both conditions disrupt homeostasis and can be fatal if untreated.

Clinical Features ๐ŸŒก๏ธ


  • Hyperthermia: sweating, headache, dizziness, nausea, vomiting, confusion, seizures, loss of consciousness.
  • Hypothermia: shivering (initially), numbness, lethargy, confusion, slurred speech, bradycardia, loss of consciousness.
  • Symptoms vary with severity and duration of exposure.
  • Monitor for signs of complications such as heat stroke or frostbite.
  • Symptoms can be subtle, especially in elderly or those with altered mental status.
  • Prompt recognition is critical for successful management.


  • Hyperthermia: elevated core temperature (>38.5ยฐC), tachycardia, hypotension, dry skin (in heat stroke), altered mental status.
  • Hypothermia: core temperature <35ยฐC, bradycardia, hypotension, hypoventilation, cold and pale skin, areflexia in severe cases.
  • ECG changes: J waves (Osborn waves) in hypothermia.
  • Lab findings: metabolic acidosis, hyperkalemia in severe hypothermia; elevated liver enzymes, CK in hyperthermia.
  • Assess for co-existing injuries or conditions (e.g., trauma, infection).
  • Document vital signs frequently to monitor trends.

Investigations ๐Ÿงช


  • Core temperature measurement: rectal or esophageal probe for accuracy.
  • Blood tests: FBC, U&Es, glucose, ABG, lactate.
  • ECG: to detect arrhythmias and other cardiac changes.
  • CXR: to rule out aspiration pneumonia or other pulmonary issues.
  • Urinalysis: to check for myoglobinuria in hyperthermia.
  • Coagulation profile: in severe cases of hyperthermia or hypothermia.
  • Imaging: CT head if altered mental status persists.
  • Blood cultures: if sepsis is suspected.
  • Monitor glucose and electrolytes closely during treatment.

Management ๐Ÿฅผ


  • Hyperthermia:
    • Rapid cooling: ice packs, cool IV fluids, cooling blankets.
    • Hydration: IV fluids to prevent dehydration.
    • Treat underlying cause: discontinue causative drugs, manage infections.
    • Monitor for complications: renal failure, DIC, rhabdomyolysis.
  • Hypothermia:
    • Rewarm slowly
    • Passive rewarming: remove wet clothing, cover with blankets.
    • Active external rewarming: warm blankets, heating pads.
    • Active internal rewarming: warm IV fluids, warm humidified oxygen.
    • Treat underlying conditions: correct hypoglycaemia, manage infections.
    • Monitor for complications: arrhythmias, coagulopathy, electrolyte imbalances.
  • Regularly reassess temperature, cardiovascular, and respiratory status.
  • Consider ICU admission for severe cases.


  • Hyperthermia:
  • Heat stroke, multi-organ failure, rhabdomyolysis, DIC, renal failure.
  • Hypothermia:
  • Cardiac arrhythmias, respiratory failure, renal impairment, coagulopathy, infection risk.
  • Both conditions can lead to death if not promptly treated.
  • Close monitoring and early intervention are crucial to prevent complications.
  • Identify and manage underlying causes to improve outcomes.
  • Patient education on prevention and early signs can reduce incidence and severity.
  • Rehabilitation may be needed for patients with severe complications.


  • Depends on the severity of temperature disturbance and timeliness of treatment.
  • Early recognition and intervention improve outcomes significantly.
  • Long-term sequelae possible in severe cases.
  • Mortality higher in extremes of age and those with comorbidities.
  • Prevention strategies and patient education crucial for at-risk populations.
  • Regular follow-up and monitoring may be necessary for patients with significant complications.
  • Prognosis generally good with prompt and appropriate management.
  • Multidisciplinary approach can enhance recovery and prevent recurrence.

Key Points

  • Hyperthermia and hypothermia are medical emergencies requiring prompt treatment.
  • Differentiate from fever; hyperthermia and hypothermia are due to failed thermoregulation.
  • Monitor core temperature, electrolytes, and organ function closely.
  • Management involves gradual rewarming or cooling, treating underlying causes, and preventing complications.
  • Patient education and prevention strategies are essential to reduce incidence and severity.
  • Refer to UK guidelines for specific management protocols and recommendations.
  • Multidisciplinary care improves outcomes and supports recovery.

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