Severity of Metabolic Acidosis as a Determinant of Bicarbonate Requirements

In the treatment of metabolic acidosis, the dose of sodium bicarbonate is usually calculated on the assumption that administered bicarbonate distributes in a space equivalent to 50 per cent of body weight. In a patient with profound metabolic acidosis the apparent space of distribution of bicarbonate was over 200 per cent of body weight, although no excessive ongoing acid production or external bicarbonate losses were evident, suggesting that the pre-existing plasma bicarbonate concentration can influence the apparent space of distribution of bicarbonate. This hypothesis was tested with a standard dose of bicarbonate (2.5 mmoles per kilogram of body weight) in 16 dogs with low, normal or high plasma bicarbonate concentration. The concentration increased by 2.8, 5.0 and 5.6 mmoles per liter in the three groups respectively, indicating that the proportion of administered bicarbonate passing into the intracellular space increases with decreasing concentration. In conditions of profound metabolic acidosis, commonly recommended amounts of bicarbonate may produce unexpectedly small increments in the plasma concentration. (N Engl J Med 289:121–126, 1973)