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The targets for the ideal PD prescription continue evolving with time. Serious attempts have been made to quantitate the amount of solute removal required for best patient outcomes, based on the available clinical data. These initiatives have been limited by inability to identify the best biochemical markers of uremia, the confounding role of residual renal function (RRF), the influence of volume control on outcome and the complexity of comorbid conditions affecting patients with renal insufficiency. During the past decade, many organizations have proposed targets for the PD prescription based on whatever evidence is available, whenever possible, and in the absence of evidence, on the consensus of expert opinion. Because of the wealth of information available, most of these recommendations are based on small solute removal.
Clearances for urea and creatinine are easy to measure and have been shown to correlate with patient survival in many studies. Their clearance is generally normalized to some measure of body mass. In the case of urea, a popular index is the dimensionless Kt/V, where K denotes urea clearance in ml/min, t is time in min and V is the volume of distribution of urea or total body water. Creatinine clearance (Ccr) is usually normalized for body surface area and expressed as ml/min/1.73 m2.
The National Kidney Foundation Dialysis Outcomes Initiative (KDOQI™) was the first formal set of guidelines for PD adequacy. Its methodology is based on a scientifically rigorous process, using evidence-based rationale whenever possible, a critical review of the literature and a clear distinction between evidence-based and opinion-based recommendations. Despite its limitations, it has generated much discussion and heightened the interest in quantitation of dialysis dose. Their current basic recommendations for PD dose are:
- Weekly total (peritoneal and kidney) Kt/V > 1.71
- No differentiation between CAPD and APD, nor RRF status, as indicated in previous guidelines
- No recommendations for creatinine clearance
- “Determination of peritoneal creatinine is of little added value for predicting risk of death, therefore for simplicity, the adequacy targets are based on urea kinetics only”
These guidelines are intended for minimal dose, rather than targets, and emphasize that all patients should be above the minimum. The importance for careful patient monitoring with prescription adjustment, as needed cannot be over emphasized. These recommendations are based mainly on two short-term trials from Mexico (ADEMEX)2 and Hong Kong3.
Re-analysis of CANUSA study (2001) showed that residual kidney function, rather than peritoneal clearance, was associated with improved survival4. This confirmed earlier reports in the literature based on extensive FMC-NA data (2000)5.
The Canadian Society of Nephrology (CSN) Guidelines for Peritoneal Dialysis Adequacy are being revised and will be posted upon publication.
All targets are intended to guide the clinician in prescribing the doses generally identified as adequate for the typical patient, but by no means are these recommendations intended to be a substitute for good medical judgment and attention to other important aspects of medical care. In fact, many of these suggested guidelines also address the importance of good nutrition and adequate volume control, important components of optimal renal care. |