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CDHB

Hyperthermia

Definition - 'heat stroke' - temperature greater than 41^oC with altered mental status (confusion to coma), with underlying dysfunction of the heat regulatory mechanism. It may be a continuum of 'heat exhaustion' which is a systemic reaction to prolonged heat exposure and is characterized by salt and water depletion. Cardiovascular and respiratory stimulation and sweating eventually give way to depression and a hot dry skin. Many systems can be damaged, and complications like rhabdomyolysis, renal failure, and coagulopathy are common.

Initial assessment and resuscitation

• Airway, Breathing, Circulation: Supplemental oxygen
  • Large volumes of fluid may be required to resuscitate.
  • Subsequent fluid management is aimed at maintaining a urine output of >50 mL/hour and may best be guided by invasive monitoring of the circulation in ICU.
• Cooling measures:
  • Rapid cooling is essential.
  • Remove all clothing.
  • Apply ice packs to groin, axillae, and neck (large superficial vessels).
  • Alternatively, thoroughly douse in iced water if available (ice slurry in towels). Spray with water and fan to cause evaporation. If done well this may be the most effective means of cooling.
  • Cooled peritoneal lavage has been used but other invasive 'lavages' have not been well evaluated in humans.

    Note: Tentative cooling may simply cool the skin and further limit heat loss by the core. Be aggressive.

Complete assessment

History

• Usually exposure to extreme heat or strenuous activity in the heat.
• There may be contributing factors e.g., elderly, infirm, cardiovascular disease, cystic fibrosis, diabetes, alcoholism, obesity, infection, anaesthetic agents (via a muscle hypermetabolic state and requiring treatment with dantrolene - contact ICU and the Duty Anaesthetist if secondary to suxamethonium, inhalational or local anaesthetic agents), antipsychotic and other drugs (via a central dopamine blocking action).

Examination: directed to causes and complications.

Investigations: directed clinically, but including CBC + diff, coagulation profile, urea, creatinine, LFTs, Na, K, Ca, CK, urine for myoglobin.

Definitive management

Usually cooling/monitoring continues in ICU including management of the many potential complications.

Topic Code: 1277