Clinical findings in heat stroke

Heat stroke is an uncommon but life-threatening condition, in which the body’s ability to dissipate heat is lost, resulting in organ system failure. Heat stroke can be:

• classic (nonexertional)—typically occurs in the elderly and those with chronic disease, who may have impaired thermoregulation or be unable to remove themselves from a hot environment
• exertional—occurs in individuals engaging in strenuous exercise, mostly during periods of high ambient temperature and humidity. Recent evidence suggests a small number of individuals have a genetic predisposition to exertional heat stroke in normal ambient conditions (an association between exertional heat-related illness and malignant hyperthermia has been suggestedPoussel, 2015Roux-Buisson, 2016.

The key clinical features of heat stroke are:

• altered mental state or neurological signs (lethargy, confusion and ataxia may progress to a decreased state of consciousness and generalised seizures) AND
• core body temperature 40ºC or higher¹; see Measurement of core body temperature in heat-related illness for details about the challenges of measurement. When assessing a patient in hospital, be aware that prehospital cooling interventions may mask the diagnosis.

Many patients have hot, dry skin because they have stopped sweating (particularly in nonexertional heat stroke), but the absence of sweating is not useful for diagnostic or prognostic assessment.

Patients may be hypovolaemic due to vasodilation and excessive sweating.

Other physical findings of heat stroke may include abnormalities in the following systems:

• cardiovascular—circulation may appear hyperdynamic with tachycardia, dyspnoea and crackles (noncardiogenic pulmonary oedema)
• respiratory—an increase in respiratory rate and minute volume is present unless the patient is obtunded (lethargic, slow to respond, drowsy)
• haematological—petechial haemorrhages, bruising and overt bleeding as disseminated intravascular coagulation (DIC) develops
• musculoskeletal—rhabdomyolysis may present with muscle pain, and tenderness on palpation. A high index of suspicion is necessary.