Three patients with elevated blood lactate values are described. The first, despite moderate hyperlactatemia of 5.3 mEq./1. and severe acidosis with an arterial blood pH of 6.98, had no “excess lactate”. In a second patient, moderate acidosis with a pH of 7.27 and blood lactate of 7.5 mEq./1., of which 33% was excess lactate, was found to be secondary to tissue hypoxia on an ischemic basis and preceded the onset of clinical shock by four hours. A third patient, diabetic and under treatment with phenformin hydrochloride, presented with many features suggestive of pulmonary embolism, including marked pulmonary hypertension. A diagnosis of idiopathic lactic acidosis was established when the arterial blood pH was found to be 6.77 and a blood lactate value of 14.2 mEq./1., 60% as excess lactate, was discovered in the absence of a demonstrable cause of tissue hypoxia. Exploration of the pulmonary vascular bed showed no sign of mechanical blockage. The diagnostic, therapeutic and prognostic value of measuring blood lactic acid, and of quantitating the proportion circulating as “excess lactate”, is emphasized.
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