Net protein utilization during total parenteral nutrition of injured critically ill patients: an original approach

Traumatized critically ill patients with either a moderate or severe catabolic response were studied. Patients were randomly allocated to receive an intravenous solution which was either protein-free or contained protein and hypertonic glucose. The overall energy intake in both groups was equivalent to each patient's daily requirement. In both the moderately catabolic and severely catabolic patients the urinary nitrogen loss with the protein-free solution was negatively correlated to the energy intake/energy need ratio (p less than 0.01, moderate catabolism; p less than 0.001, severe catabolism). The ratio of energy intake/energy need was correlated with the nitrogen loss. From the resultant straight line, the obligatory nitrogen loss was determined for those patients receiving the protein containing solution (test diet). The net protein utilization was subsequently calculated using this value of the obligatory nitrogen loss. The net protein utilization was inversely correlated with the severity of trauma. It was significantly (p less than 0.005) greater in the patients with a moderate catabolic response. In the acute postinjury phase, the net protein utilization of infused amino acids was similar to that for protein fed orally to normal healthy subjects.