Urea is the best molecule to target adequacy of peritoneal dialysis.
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.
Department of Medicine, University of California, San Francisco, USA.
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D003404:Creatinine / Q000493:pharmacokinetics; D005260:Female; D006801:Humans; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D010530:Peritoneal Dialysis / Q000379:methods / Q000592:standards*; D014508:Urea / Q000493:pharmacokinetics*; D014511:Uremia / Q000517:prevention & control
D014508:Urea; D003404:Creatinine