Urea is the Best Molecule to Target Adequacy of Peritoneal Dialysis

Abstract

For hemodialysis, a large base of data shows the validity of modelling the dialysis dose and reliably estimating protein intake from equilibrated Kt/V urea (eKt/VU), the total dialyzer urea clearance provided during each treatment divided by the urea distribution volume. An eKt/VU of 1.05 thrice weekly is judged adequate, but is still under study. In continuous ambulatory peritoneal dialysis (CAPD), two dosage criteria are widely recognized: continuous ("standard") Kt/VU (stdKt/VU = 2.0 weekly), and total creatinine (Cr) clearance normalized to body surface area (KCrT = 70 L/week/1.73 m2). The CANUSA study concluded that a stdKt/VU of 2.1 and a KCrT of 70 L/week/1.73 m2 gave equivalent clinical outcomes. The Dialysis Outcomes Quality Initiative (DOQI) recommends values of 2.0 and 60 L/week/1.73 m2 respectively. An analysis of these two parameters for males and females over a wide range of body surface areas (BSAs) was done and the analysis showed: (1) The U and Cr dose criteria are incommensurable--that is, they can virtually never be achieved simultaneously in anephric patients. (2) The Cr criterion varies widely with the sex of the patient and with the BSA-dependent variation in stdKt/VU over a range of 2.1 to 3.0. (3) The U criterion always produces a KCrT < 60 L/week/1.73 m2 in females and 60-70 L/week/1.73 m2 in males. With respect to U and Cr, the CANUSA results were concluded to be valid in patients with substantial residual renal function, but probably not applicable to anephric patients where the doses are clearly incommensurable.