Assessment of Urea Appearance Rates and Net Nitrogen Deficits in Patients With Acute Renal Failure Receiving Continuous Venovenous Hemofiltration

Abstract

■ Objective: To investigate the impact of the nutritional regimen on the urea appearance rate (UAR) and net nitrogen deficit (NND) in patients with acute renal failure (ARF) receiving continuous venovenous hemofiltration (CWH). Comparison of estimated energy expenditure using a modification of the Harris-Benedict equation versus measured energy expenditure was performed. ■ Design: Noninterventional study with prospective data collection. ■ Setting: Tertiary care hospital. ■ Patients: Forty consecutive patients age 52 ± 20 years (mean ± SD) with ARF who required CWH between June 1991 and June 1992. ■ Interventions: Noninterventional study. ■ Main outcome measures: UAR and NND were calculated for each study day. Total calories, nonprotein calories, and grams of protein per day, and estimated energy needs were quantified for all patients. Energy expenditure was measured for 10 patients. ■ Results: Patients were treated with CWH for a total of 357 days. Estimated energy needs (2,408 ± 515 kcal/d) correlated well with measured energy needs (2,348 ± 706 kcal/d; r = 0.78). The mean UAR was 13.2 ± 4.7 g N/d. There was no difference in mean UAR between patients receiving less than 1.0 g versus 1.0 g or more of protein/kg/d. The mean NND was −8.3 ± 6.1 g N/d. Those patients receiving 1.0 g or more of protein/kg/d (n = 16) had a significantly lower NND than those patients who received less. Five patients receiving 1.0 g or more of protein/kg/d achieved a positive nitrogen balance. These patients had a nonprotein calorie-to-nitrogen ratio (132 ± 37) that was significantly less than that administered to patients who did not achieve a positive nitrogen balance (169 ± 33; P > 0.05). ■ Conclusions: Estimated energy expenditures using a modified Harris-Benedict equation provided moderate predictability with measured energy expenditures. The provision of 1.0 g or more of protein/kg/d did not increase the UAR and was associated with a decreased NND. The provision of a lower nonprotein calorie-to-nitrogen ratio in patients receiving 1.0 g or more of protein/kg/d was associated with a positive nitrogen balance.