A reappraisal of nitrogen requirements for patients with critical illness and trauma

BACKGROUND: Studies regarding protein requirements for patients with critical illness are inconclusive owing to small sample size and population heterogeneity. The primary objectives of this study were to determine the amount of protein required to achieve nitrogen equilibrium or a positive nitrogen balance (NB, -4 g/d or better) and ascertain whether patients with traumatic brain injury (TBI) exhibit greater protein catabolism than those without TBI. METHODS: Adult patients admitted to the trauma center, given specialized nutrition support, and had an NB determination within 5 days to 14 days after injury were evaluated. Patients with obesity, incomplete urine collection, kidney disease, corticosteroid or pentobarbital therapy, or an oral diet were excluded. RESULTS: A total of 300 NB determinations from 249 patients were evaluated. Increasing the protein dosage generally resulted in improved NB; however, the data were highly variable. Of the patients who received a protein intake of 2 g/kg per day or greater, 54% achieved nitrogen equilibrium or positive NB (-4 g/d or better) in contrast to 38% and 29% of patients who received 1.5 g/kg per day to 1.99 g/kg per day and 1 g/kg per day to 1.49 g/kg per day, respectively (p < 0.001). There was no significant difference in NB between patients with and without TBI at similar protein intakes. CONCLUSION: A higher protein intake was generally associated with an improved NB; yet, many patients remained having a negative NB. A protein dosage of 2 g/kg per day or greater was more successful in achieving nitrogen equilibrium than were lower-dosage intakes. Patients with TBI do not exhibit significantly greater protein catabolism than do patients without TBI. (J Trauma Acute Care Surg. 2012;73: 549-557. Copyright (c) 2012 by Lippincott Williams & Wilkins)