Obligatory Negative Nitrogen Balance Following Spinal Cord Injury

Abstract

Obligatory nitrogen losses due to paralysis in the spinal cord-injured (SCI) patient prevent positive nitrogen balance (NB) regardless of the calorie and protein intakes. Ten patients with SCI and 20 controls with nonspinal cord injury (NSCI) matched for time, sex, age, and injury severity score (ISS) were admitted to our Level I trauma center. In both groups, total nutritional support was delivered within 72 hours of admission based on predicted energy expenditures (PEE = Harris-Benedict equation x 1.2 x 1.6) and 2 g of protein/kg of ideal body weight (IBW). Subsequent changes in nutrient delivery were based on NB. No SCI patient established positive NB during the 7-week period following injury despite an average delivery of 2.4 g of protein/kg IBW and 120% of the PEE at the time of peak negative NB (-10.5). In six SCI patients, an average increase of 25% in delivered protein and 12% in delivered calories over a 1-week period effected no change in average NB (-7.4 vs -6.8). Indirect calorimetry in five SCI patients showed that calorie intakes were 110% more than average measured energy expenditures. In contrast, 17 of 20 NCSI patients achieved positive NB within 3 weeks of admission. They required an average delivery of 2.3 g of protein/kg IBW and 110% of PEE to reach positive NB. These data demonstrate the phenomenon of obligatory negative NB acutely following SCI. Aggressive attempts to achieve positive NB in these patients will fail and result in overfeeding.