ANALYSIS OF THE UREA GENERATION RATE AND THE PROTEIN CATABOLIC RATE IN HEMODIALYZED PATIENTS

The urea generation rate (G) and the protein catabolic rate (PCR) have been investigated in two groups of hemodialyzed patients over a whole week cycle, one with zero residual renal function (Kr = 0) dialyzed thrice weekly and the other dialyzed twice weekly with nonzero residual renal function, The two-pool model of urea kinetics was used. No relationship between patients' age and the PCR was found, and also no difference in the PCR between males and females was seen. All patients with a PCR < 0.8 g/kg/day had a midweek predialysis plasma urea level well below 25 mmol/L, which clearly documents the value of a kinetic approach in early detection of patients at risk for malnutrition. In the thrice weekly dialyzed group, a statistically significant relationship was found between PCR and KT/V: PCR = 0.582 + 0.253 x KT/V, r = 0.374 with p < 0.05. In the twice weekly dialyzed group with nonzero Kr, contribution of the residual renal function had to be included into KT/V to reach a level of statistical significance of PCR = 0.697 + 0.18 x KT/V, r = 0.481 with p < 0.05. With regard to values of Kr encountered in the investigated group (0-3.5 ml/min), its influence upon PCR is higher than a volumetrically equal increase in excretorial efficacy of the artificial kidney. The G in the thrice weekly dialyzed group was found to be dependent on the length of the interdialytic interval over which it was evaluated, Over the intervals Friday-Monday, Monday-Wednesday, and Wednesday-Friday the following mean values of G were obtained: 0.155, 0.180, and 0.188 mmol/min, respectively, This finding suggests a physiological link between urea generation and its excretion, possibly mediated via its concentration in body fluids. The time constant of this link is apparently quite short, on the order of hours or a few tens of hours. It also indicates that the metabolic status of a dialyzed patient may be influenced not only by the dialysis dose as defined by the KT/V value but also by the overall time schedule of treatment.