Investigations

1st investigations to order

rectal temperature

Test
Result
Test

Measure rectal temperature in all patients with suspected heat stroke.[1][2] 

  • Rectal temperature is the most accurate measurement of core hyperthermia compared with axillary, oral, or aural thermometry.[1][2] 

In practice, consider using an oesophageal probe in intubated patients.

Do not delay treatment if temperature is lower than the diagnostic threshold of 40°C in a patient with hyperthermia and an altered level of consciousness.[2] See the Management section.

Practical tip

Be aware that patients presenting with normal temperature can have heat stroke, either because of inaccurate measuring techniques or from effects of prior cooling (e.g., in the community). Continue to monitor the patient's temperature while cooling. See the Management section.

Result

>40°C (heat stroke)

FBC

Test
Result
Test

Neutrophilia, anaemia, and thrombocytopenia may be present.

Result

variable; may show neutrophilia, anaemia, and thrombocytopenia

liver function tests

Test
Result
Test

Elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST) due to heat-induced liver damage.

Result

variable; elevated ALT and AST

renal function tests

Test
Result
Test

Elevated creatinine and urea due to reduced renal perfusion.

Result

elevated creatinine and blood urea

glucose

Test
Result
Test

Hypoglycaemia may occur in patients with exertional heat stroke and in patients with fulminant hepatic failure.

Result

usually normal; may show hypoglycaemia in exertional heat stroke or in fulminant hepatic failure

electrolytes

Test
Result
Test

Hyper/hyponatraemia and hyper/hypokalaemia may be present due to volume depletion.

Result

variable; hyper/hyponatraemia, hyper/hypokalaemia

arterial blood gases

Test
Result
Test

Metabolic acidosis and respiratory alkalosis are the most common abnormalities due to poor peripheral perfusion.

Result

variable; metabolic acidosis and respiratory alkalosis; elevated lactate

creatine kinase

Test
Result
Test

Elevated in rhabdomyolysis, a frequent complication of heat stroke.

Result

variable; elevated creatine kinase (>1000 U/L) is common

clotting profile

Test
Result
Test

Prolonged clotting times are due to heat-induced liver damage and disseminated intravascular coagulation, a frequent complication of heat stroke.

Result

variable; may show elevated prothrombin time, activated PTT, and INR; hypofibrinogenaemia

urinalysis

Test
Result
Test

Rhabdomyolysis (myoglobinuria) and other evidence of renal injury may be present.[10] 

Result

myoglobinuria and/or haemoglobinuria

ECG

Test
Result
Test

Perform an ECG and monitor continuously for possible arrhythmias.[10] Other ECG changes may be non-specific (e.g., conduction abnormalities and non-specific ST/T wave changes).[10]

Result

may show arrhythmias, conduction abnormalities, and non-specific ST/T wave changes

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