Cysteine usage increases the need for acetate in neonates who receive total parenteral nutrition.

The addition of cysteine (as cysteine HCl) to a total parenteral nutrition (TPN) solution enhances calcium and phosphate solubility because cysteine lowers the pH of the solution. To determine whether adding cysteine to TPN solutions affected the acid-base homeostasis of infants and increased their need for acetate to obviate acidosis, we studied two groups of neonates--those receiving TPN before (group C) and after (group NC) the addition of cysteine. Measurements were made before and during the first 2 wk of TPN administration. We measured the pH of our standard TPN solution with and without the addition of cysteine. Serum carbon dioxide was significantly lower in group C despite a significantly greater intake of acetate in group NC. In the in vitro study the addition of cysteine to the TPN solution lowered the pH from 5.5 to 5.1. Newborns who received TPN solutions to which cysteine was added had lower serum carbon dioxide values and a greater need to receive acetate than did newborns who received TPN solutions without cysteine.