AN ANALYSIS OF ADEQUACY OF DIALYSIS IN A SELECTED POPULATION ON CAPD FOR OVER 3 YEARS - THE INFLUENCE OF UREA AND CREATININE KINETICS

Adequacy of dialysis is addressed to minimize the negative consequence s of underdialysis. The results of the NCSD demonstrated that urea kin etic modelling (UKM) is a useful tool in the measurement of adequacy o f dialysis: Kt/V values of 1 are considered adequate to prevent compli cations when daily protein intake is appropriate. For CAPD no similar prospective studies exist, and consequently there is no information co mparable to that for haemodialysis. Preliminary data have communicated controversial results about the usefulness of UKM for CAPD prescripti on. On the other hand creatinine kinetics has been proposed as an alte rnative to UKM to define adequacy of dialysis on CAPD. However, these results should be considered preliminary because of the small size of the series and the short observation period. The objective of this pap er is to study the role of these two kinetic models in defining adequa cy of dialysis in a long-term, selected CAPD population. We have studi ed 56 patients treated for at least 3 years on CAPD (3-11 years; mean observation period 5 years; 3996 patient-months). Urea kinetic model ( UKM) (urea weekly (W) Kt/V and NPCR) and creatinine kinetics (Efficacy number (EN) and K) were determined annually. According to the present data we can conclude that Kt/V is an appropriate tool for defining ad equacy in patients on CAPD. Values of weekly Kt/V greater than 1.7-1.8 , with NPCR more than 1 g/kg/day, assure an adequate clinical outcome. Conversely, values on the Kt/V scale less than 1.7 entail a greater r ate of complications. Our data also confirm that maintaining a serum a lbumin > 536-551 mumol/l (3.7-3.8 g/dl) is related to lower morbidity and mortality, and should be a major objective for CAPD patients. Cons equently a relationship between dose of dialysis in terms of urea mass balance and protein nutrition can be established. After 5 years on CA PD, when all residual renal function is generally lost, Kt/V values in excess of 1.9 are difficult to achieve. Based on currently available information, we do agree with the interest of performing a prospective study on adequacy of dialysis based on the urea kinetic model in CAPD , which definitely defines its role. On the other hand, creatinine kin etics did not show sufficient discriminative capacity in terms of adeq uacy of dialysis. EN and Kt of creatinine values in the lower range (4 .5-6 and less than 45-50 l/week respectively) were not necessarily ass ociated with a poorer clinical outcome. Patients with peritoneal high diffusive capacity for small molecules showed a tendency toward protei n malnutrition and poorer clinical outcome compared to those with low diffusion capacity. Consequently, low diffusive peritoneum capacity sh ould no longer be considered a contraindication for CAPD.