Evaluation of nitrogen utilization in patients receiving total parenteral nutrition

This two phase study evaluates nitrogen utilization by the body as a function of fixed caloric intake but different nitrogen loads. Nitrogen use by the body was estimated from measures of nitrogen balance, net protein utilization, and urea accumulation rate. Phase 1 of this study included 411 measurements of nitrogen use in 120 patients assigned, according to clinical condition, to receive one of the four following therapies: dextrose (D) 25%, amino acids (CAA) 4.25% (Group 1); D 35%, CAA 4.25% (Group 2); D 25%, CAA 2.13% (Group 3); or D 35%, CAA 2.13% (Group 4). Forty patients in Phase 2 were assigned in a randomized, prospective, double blind manner, to receive one of the following regimens: D 35%, CAA 2.75% (Group 5); D 25%, CAA 2.75% (Group 6); D 35%, CAA 4.25% (Group 7); or D 25%, CAA 4.25% (Group 8). In Phase 1, positive nitrogen balance was achieved with the exception of Group 3 where neither the estimated caloric nor nitrogen needs of the patients were met. It appeared that protein utilization was maximal in patients receiving the therapy of highest calorie:nitrogen ratio (Group 4). Phase 2 patients achieved positive nitrogen balance to the same extent (p > 0.05) and although net protein utilization improved from 53 to 71%/d as the calorie:nitrogen ratio was increased, the differences were not significant (p > 0.05). There was a significant improvement in total iron binding capacity in Phase 2 patients (p < 0.01) that was most prominent at the lower concentrations of amino acids (high cal:n ratio) (Groups 5 and 6). Smaller amounts of nitrogen appear adequate in producing a positive nitrogen balance and may be better utilized in hospitalized patients if the patients' caloric requirements are achieved.