The metabolic and respiratory alterations of heat stroke.

The metabolic and respiratory changes of 21 patients with heat stroke were studied. Admission arterial blood gas levels were measured, and serum bicarbonate, lactate, calcium, phosphorus, and anion gap determinations were performed. Seven patients had a metabolic acidosis (pH 7.20 +/- 0.04, PCO2 32 +/- 2 mm Hg, and bicarbonate 12 +/- 1 mEq/L), seven a combined metabolic acidosis and respiratory alkalosis (pH 7.39 +/- 0.01, PCO2 25 +/- 1 mm Hg, and bicarbonate 15 +/- 1 mEq/L), four a respiratory alkalosis (pH 7.45 +/- 0.01, PCO2 30 +/- 1 mm Hg, and bicarbonate 20 +/- 1 mEq/L), one a metabolic and respiratory acidosis (pH 7.13, PCO2 52 mm Hg, and bicarbonate 17 mEq/L), and one a respiratory acidosis (pH 7.30, PCO2 56 MM Hg, and bicarbonate 27 mEq/L). The 15 patients with a metabolic acidosis had a pH of 7.28 +/- 0.03, PCO2 of 30 +/- 2 mm Hg, bicarbonate level of 14 +/- 1 mEq/L, lactate concentration of 6.5 +/- 1.0 mEq/L, and an anion gap of 26 +/- 4 mEq/L. Nine patients were hypocalcemic (7.8 +/- 0.3 mg/dL), and five patients were hypophosphatemic (2.0 +/- 0.2 mg/dL). The predominant metabolic change in heat stroke is a metabolic acidosis secondary to increased lactate content and/or a respiratory alkalosis. Hypocalcemia is common and hypophosphatemia is not infrequent.