Comparison of urinary urea nitrogen excretion and measured energy expenditure in spinal cord injury and nonsteroid-treated severe head trauma patients.

Severe head trauma patients (HT) exhibit markedly elevated energy expenditure and 24-hr urinary urea nitrogen excretion (UUN) values. The objective of this study was to compare seven spinal cord injured patients (SCI) to seven HT for changes in UUN and measured energy expenditure (MEE) over the first 18 days following injury. Energy expenditure was measured by indirect calorimetry and compared to values predicted by the Harris Benedict Equation (PEE). There were six quadriplegics and one paraplegic in the SCI group. HT patients had peak Glasgow Coma Scale scores of 3 to 10 for the first 24 hr postinjury. Patients were studied prospectively and matched for age, sex, and admitting weight Week 1 following the injury, SCI had mean UUN values of 0.18 +/- 0.04 g/kg/day vs 0.18 +/- 0.01 for HT patients. The mean MEE/PEE ratio was 0.56 for the SCI and 1.4 for HT (p less than 0.01). Over the entire study period the mean UUN value for SCI was 0.23 +/- 0.03 g/kg vs 0.21 +/- 0.01 for HT. The mean MEE/PEE ratio for SCI was 0.94 while HT remained elevated at 1.5 (p less than 0.05). Although the UUN was comparable in SCI vs HT, there was a significant difference in MEE/PEE between the groups. The elevation in UUN observed in SCI is not due to a hypermetabolic state. This suggests that different mechanisms promote the increased nitrogen excretion observed in these two populations.