Protein and calorie requirements with total parenteral nutrition

Body composition measurements, performed by multiple isotope dilution, were used to determine the protein and caloric requirements of patients receiving total parenteral nutrition (TPN). In addition the relative efficacy of lipid as opposed to carbohydrate calories were evaluated. Patients requiring TPN were randomly allocated to receive one of the following TPN solutions: a) 2.5% amino acid with 25% dextrose b) 5% amino acid with 25% dextrose c) 2.5% amino acid with 12.5% dextrose and a 5% lipid emulsion. The efficacy of each solution was evaluated by determining body composition at the onset,and at two week intervals during the course of TPN. In 204 patients who received TPN for 4447 days, 533 body composition studies were performed to evaluate 308 periods of TPN. In the normally nourished patient, as defined by the pre-TPN body composition, the body composition remained unchanged and normal with the three solutions. In the presence of preexisting malnutrition, two weeks of TPN resulted in a significant increase in body weight, arising primarily from an increase in the body cell mass. To evaluate the relative importance of the various factors responsible for the increase in the body cell mass, a multiple linear regression analysis was performed. The mean daily change in the body cell mass was correlated with the carbohydrate, protein and lipid calories infused and with the nutritional state. The resulting regression equation, which was statistically significant, indicated that the rate at which a depleted body cell mass was restored was related to the lipid and carbohydrate calories infused and to the nutritional state of the patient. Carbohydrate calories were more efficient than lipid calories. However increasing the amino acid concentration from 2.5 to 5% had no effect on the rate at which the body cell mass increased. The repletion rate was also directly related to the severity of malnutrition. Thus the correction of a malnourished individual with TPN is dependent on the severity of malnutrition, the type and amount of calories infused but is not affected by increasing the amino acid concentration from 2.5 to 5%.