Production, Excretion, and Net Balance of Fixed Acid in Patients with Renal Acidosis*

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Abstract
A new technique for the measurement of net external acid balance was applied to the study of patients with chronic renal acidosis. On a standard liquid formula diet patients with renal acidosis produced as much fixed acid as did normal subjects. During the development of renal acidosis in 4 patients, the acid balance was positive. The amount of acid retained was significantly greater than that required to produce the observed fall in extracellular bicarbonate, suggesting that some of the acid was buffered by intracellular base. In 8 patients with chronic stable acidosis the acid balance was also positive. Approximately a 1/3 of the daily endogenous acid load failed to be excreted in the urine, yet extracellular bicarbonate did not change. When plasma bicarbonate was maintained at normal levels in 6 of these patients by the continuous administration of sodium Bicarbonate, the positive acid balance was ablished in five. The data indicate that acidosis in patients with renal disease calls into play an extrarenal mechanism that neutralizes the acid not excreted in the urine, and thereby helps to stablize plasma bicarbonate. The nature of this extrarenal mechanism is not revealed by these studies, but neutralization of acid by reaction with bone salts is an attractive hypothesis.