Failure of nonprotein calories to mediate protein conservation in brain-injured patients.

Nitrogen balance in response to varying caloric intake was studied in 17 non-steroid-treated patients with isolated severe head injury (Glasgow Coma Scores, 4-9). Nitrogen excretion was found to remain relatively stable or to rise in response to protein intake over a wide range of nonprotein calorie intakes. Urine urea nitrogen excretion was not related to caloric intake, but was correlated (p less than 0.04) with nitrogen intake. In this study protein conservation was not achieved by increasing caloric intake up to and beyond two times the basal energy expenditure in the brain-injured patient. In these patients nitrogen balance could only be achieved by nitrogen intakes in excess of the high protein catabolic rate. These findings argue for a central control mechanism for protein catabolism that is independent of the magnitude of peripheral tissue injury.