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■ 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.

Patients with acute renal failure are in substantial negative nitrogen balance as a result of their extremely high protein catabolic rates. We prospectively evaluated a series of patients with acute renal failure managed with continuous venovenous hemofiltration to determine which nutritional and nonnutritional variables might influence protein catabolism and nitrogen balance.Forty consecutive patients (aged 52 +/- 20 years; mean +/- SD) were monitored for 357 treatment days (average treatment duration 8.9 +/- 8.6 days). All data (including nutritional regimen, laboratory values, APACHE II score, administered blood products, hemofiltration parameters, and medications) were collected daily.For all patients, the mean normalized protein catabolic rate was 1.4 +/- 0.5 g/kg per day. The rate did not differ between those who received nutrition support and those who did not. The net nitrogen deficit was less in those patients receiving nutrition support (-6.0 +/- 5.2 vs -14.0 +/- 5.6 g N/d; p = .02). Using regression techniques (adjusted for the within-person correlation and the previous day's normalized protein catabolic rate), the level of protein and energy provision and the interaction between protein and energy provision were predictive of the normalized protein catabolic rate. Predicted values, using this equation, suggest that at low protein administration rates (1 g/kg per day), increasing energy provision may reduce the protein catabolism. However, at this level of protein provision, patients remain in negative nitrogen balance. At protein administration rates necessary to achieve nitrogen balance (approximately 1.5 to 1.8 g/kg per day), protein catabolism may increase. Providing relatively low levels of energy may diminish the magnitude of this increase.These results suggest that the optimal nutritional regimen for patients with acute renal failure may require a high-protein (approximately 1.5 to 1.8 g/kg per day) and a relatively low-energy (approximately 25 to 35 kcal/kg per day) content.

Urea kinetic analysis allows for the calculation of the urea distribution volume and urea generation rate. This method was employed in patients with acute renal failure managed by continuous venovenous hemofiltration (CVVH). Based on serial serum urea nitrogen concentration measurements, each patient's treatment course consisted of both steady state and non-steady state periods. Thirteen data sets were obtained from 11 critically ill patients treated with CVVH. The duration of therapy was 9.5 +/- 7.5 days (mean +/- SD). Serum urea nitrogen concentration fell from 114 +/- 32 mg/dl to a steady state value of 79 +/- 17 mg/dl (p < 0.0005). The urea distribution volume was 0.55 +/- 0.11 L/kg (range 0.29-0.73), and the urea generation rate 11.7 +/- 3.1 mg urea N/min (range 7.1-17.3). The steady state serum urea nitrogen concentration had a linear relationship to the rate of urea generation (r = 0.92). Urea kinetic analysis permitted the simultaneous determination of the urea generation rate and distribution volume, on an individualized basis, in patients with acute renal failure treated with CVVH.