The influence of synthetic amino acid and casein hydrolysate on the endogenous production and urinary excretion of acid in total intravenous alimentation.

Abstract

Extract: These investigations are designed to quantitate the acidogenic properties of several commonly used amino acid solutions. Infusion of amino acid solutions causes a rise in the sulfuric acid production to a rate of 26.8–93.1 μEq/min/1.73 m2, which is a 4− to 14-fold increase over the preinfusion rate of 6.6 μEq/min/1.73 m2. This is a reflection of the amount of sulfur-containing amino acids in the infusate; it is lower with the casein hydrolysate than with the synthetic amino acid. The increase in is also significantly less with the 2.13% solutions than with the 4.25% solutions. The rate of organic acid production (H+oa) tends to be higher with the 4.25% casein hydrolysate (48.1 μEq/min/1.73 m2) than with both the 2.13% and the 4.25% synthetic amino acid solutions (22.4–29.3 μEq/min/1.73 m2). The latter value is not significantly different from the preinfusion rate of H+oa (20.4 μEq/min/1.73 m2). However, taken together, the results of these data are consistent with the view that the total amount of acid produced ( plus H+oa) in association with infusion of the synthetic amino acid solutions is proportionately higher than that associated with infusion of the casein hydrolysate. The absolute values for the acid excretion during amino acid infusions also show differences from the preinfusion state of 23.7 μEq/min/1.73 m2. The net acid excretion increased nearly four times during the infusion of the 4.25% synthetic, amino acid and casein hydrolysate solutions. The net acid excretion is shown to be linearly correlated with the net acid production (r = 0.974). On the other hand, only 65% of net acid production is excreted as net acid by the kidneys, and the extracellular buffering can account for only a fraction of the difference between the net acid production and excretion. These studies also provide the first conclusive evidence that the rate of endogenous acid production during glucose-water infusion is 26.9 μEq/min/1.73 m2 or 2–3 mEq/kg/24 hr. Speculation: The data presented suggest that the marked increase in endogenous acid production is related to the quantity and quality of amino acid-sulfur in the different type of infusates used in total intravenous alimentation and further suggest a significant nonextracellular buffering mechanism (possibly the skeletal system).