Urea kinetics: a guide to nutritional management of renal failure

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Abstract
Net protein catabolic rate (PCR) can be determined easily in stable and unstable dialysis patients and can provide nutritional information sufficient for clinical determination of nitrogen balance. PCR is estimated from the net rate of urea nitrogen generation which, with urea volume of distribution (V), can be calculated from pre, post, and pre SUN levels and treatment constants. A metabolic study in five patients showed urea nitrogen generation = 0.154 PCR − 1.7 (g/day) and verified V by urea infusions (Vinf); V/Vinf = 1.03 ± 0.02; intrapatient coefficient of variation of V was 7.33% for 34 patients (N from 10 to 56). In stable patients, PCR is used to estimate dietary protein intake (DPI) and provide rapid feedback to the dietitian and patient. In unstable patients, PCR is used to estimate the degree of nitrogen imbalance. In an acute patient with total parental nutrition, PCR was used to determine total metabolic energy for zero nitrogen balance and reverse net endogenous catabolism resulting in achievement of net anabolism and reduced dialytic requirements. In pediatric patients PCR was used with DPI to assess and modify nutritional strategy. In one patient estimated anabolism increased 75% to 26 g/day with 45% increase in DPI and 60% increase in calories. In a second patient estimated anabolism increased 18 g/day, while DPI stayed constant; calories increased 41%, while PCR decreased 31%.