Laboratory Studies
Arterial blood gas testing
Arterial blood gas analysis may reveal respiratory alkalosis due to direct central nervous system (CNS) stimulation and metabolic acidosis due to lactic acidosis. Hypoxia may be due to pulmonary atelectasis, aspiration pneumonitis, or pulmonary edema.
Lactic acidosis
Lactic acidosis commonly occurs following exertional heat stroke (EHS) but may signal a poor prognosis in patients with classic heat stroke.
Glucose
Hypoglycemia may occur in patients with EHS and in patients with fulminant hepatic failure.
Electrolytes
Sodium
Hypernatremia due to reduced fluid intake and dehydration commonly is observed early in the course of disease but may be due to diabetes insipidus. Hyponatremia is observed in patients using hypotonic solutions, such as free water, and in patients using diuretics. It also may be due to excessive sweat sodium losses.
Potassium
Hypokalemia is common in the early phases of heat stroke, and deficits of 500 mEq are not unusual. However, with increasing muscle damage, hyperkalemia may be observed.
Other
Hypophosphatemia secondary to phosphaturia and hyperphosphatemia secondary to rhabdomyolysis, hypocalcemia secondary to increased calcium binding in damaged muscle, and hypomagnesemia also are observed commonly.
Hepatic function tests
Hepatic injury is a consistent finding in patients with heat stroke.
Aminotransferase (aspartate aminotransferase [AST] and alanine aminotransferase [ALT]) llevels commonly rise to the tens of thousands during the early phases of heat stroke and peak at 48 hours, but they may take as long as 2 weeks to peak.
Jaundice may be striking and may be noted 36-72 hours after the onset of liver failure.
Muscle function tests
Creatinine kinase (CK), lactate dehydrogenase (LDH), aldolase, and myoglobin commonly are released from muscles when muscle necrosis occurs.
CK levels exceeding 100,000 IU/mL are common in patients with EHS.
Elevations in myoglobin may not be noted despite muscle necrosis because myoglobin is metabolized rapidly by the liver and excreted rapidly by the kidneys.
Complete blood cell count
Elevated white blood cell counts commonly are observed in patients with heat stroke, and levels as high as 40,000/μL have been reported. Platelet levels may be low.
Renal function tests
Elevations in serum uric acid levels, blood urea nitrogen, and serum creatinine are common in patients whose course is complicated by renal failure.
Urinalysis
Remember that urinary benzidine dipsticks do not differentiate between blood, hemoglobin, and myoglobin. Urine dipstick analyses that are positive for blood must be followed by a microscopic urinalysis to determine the presence or absence of red blood cells. Proteinuria also is common.
Cerebrospinal fluid analysis
Cerebrospinal fluid (CSF) cell counts may show a nonspecific pleocytosis, and CSF protein levels may be elevated as high as 150 mg/dL.
Other
Myoglobin causes a reddish brown discoloration of the urine but does not affect the color of plasma. This is in contrast to hemoglobin, which causes discoloration of both plasma and urine.
Procedures
Procedures may include the following:
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Endotracheal intubation
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Pulmonary artery catheter insertion
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Central venous line insertion
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Nasogastric tube insertion
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Compartment pressure measurements
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Fasciotomy
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Thoracostomy
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Peritoneal lavage
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Hemodialysis
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Sample display of equipment useful for noninvasive cooling techniques. Clockwise from top: ice pack and water, air-cooling blanket, Foley catheter, and intravenous fluids.
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Sample display of equipment useful for cooling via gastric lavage. Clockwise from top: ice water, nasogastric tube, endotracheal tube, and lavage bag.
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Sample display of equipment useful for cooling via peritoneal lavage. Clockwise from top: iced water, peritoneal catheter, and saline fluid.
