Therapy of Lactic Acidosis: Alternatives to Sodium Bicarbonate

Abstract

Lactic acidosis is the most common form of metabolic acidosis, and the current mortality from this condition is in excess of 50%. Because of its diverse pathophysiology, the clinical management of lactic acidosis is difficult. The mainstay of therapy has traditionally been the intravenous administration of sodium bicarbonate (NaHCO3), but recent clinical and experimental evidence strongly suggests that such therapy may in fact be detrimental. Lactic acidosis is generally defined as a metabolic acidosis due to the accumulation of lactic acid in the blood in excess of 5 mM, with an accompanying blood pH of less than 7.25. However, the mechanisms by which lactic acid accumulation occurs vary and include both the stimulation of lactate production and reductions of lactate metabolism. Clinically, the disorders of lactate metabolism are conveniently divided as either anaerobic (type A) or aerobic (type B) (16). The hallmark of type A lactic acidosis is tissue hypoxia, resulting in anaerobic lactic acid production. The most common causes of type A lactic acidosis are cardiopulmonary arrest and other states characterized by impaired cardiac performance, reduced tissue perfusion, and arterial hypoxemia. In these states, the hypoxia and circulatory insufficiency combine to reduce tissue oxygen availability, resulting in anaerobic metabolism and stimulation of lactic acid production. In type B lactic acidosis, on the other hand, tissue hypoxia appears not to be present, and lactic acid production is metabolically enhanced for other reasons in what is apparently an aerobic state. Examples of type B lactic acidosis include diabetes mellitus, certain malignancies, and congenital diseases of the liver that impair lactic acid metabolism. Of the two forms of lactic acidosis, type A is by far the more important clinical problem and is generally associated with a much higher morbidity and mortality. Cardiopulmonary arrest is probably the most common cause of type A lactic acidosis in the United States and Europe. Accordingly, the discussion of the therapy of lactic acidosis will focus primarily on the management of type A lactic acidosis.