The effect of nitrogen-sparing, intravenously administered fluids on postoperative body composition

The postoperative protein-sparing effect of intravenously administered amino acids was assessed quantitatively by measuring body composition by multiple isotope dilution. Body composition was determined in two groups of 19 patients each, before and on the fifth day following a major abdominal operation. One group of patients received all of their required fluids and electrolytes as a 5% glucose solution. The second group received an isocaloric infusion of protein as a 5% casein hydrolysate solution. The preoperative body composition of both groups was normal. On the fifth day after operation, the mean body weight had decreased by 2.6 plus or minus 0.6 kg in the glucose group and by 2.0 plus or minus 0.5 kg in the protein group. In the patients receiving glucose, this postoperative weight loss was due to a decrease in both body fat and the lean body mass. The mean body cell mass, which represents the total mass of living, functioning cells, decreased from 23.1 plus or minus 1.5 to 19.9 plus or minus 1.4 kg (P less than 0.001), while the extracellular mass increased from 24.9 plus or minus 0.9 to 27.3 plus or minus 0.9 kg (P less than 0.001). In contrast, in the patients receiving protein, the loss of body weight resulted entirely from a loss of body fat, while the body cell mass and the extracellular mass both remained normal. Therefore protein sparing was achieved by the postoperative infusion of protein.