Problems in Comparisons of Clearances Prescriptions in Hemodialysis and Continuous Ambulatory Peritoneal Dialysis

Abstract

There is currently great interest in defining acceptable doses of dialysis therapy with different techniques. In hemodialysis (HD) and in continuous ambulatory peritoneal dialysis (CAPD), doses of weekly clearances of urea and/or creatinine required for achieving acceptable nutrition and quality of life need better definition (1–2). If control of the peak blood urea nitrogen concentration (BUN) is important in preventing uremic toxicity (the peak concentration hypothesis), then any intermittent therapy requires a greater dose of therapy to maintain the peak concentration below or at the steady state value of CAPD (assuming the same urea nitrogen generation rate and, hence, the same weekly net removal [mass transfer] of urea nitrogen) (2). The peak concentration hypothesis remains unproven, but it is certainly compatible with the apparent need for higher weekly clearances with intermittent therapies. Accordingly, it may be appropriate to increase the weekly KTN urea for intermittent PD therapies, such as nightly peritoneal dialysis, as compared to CAPD. For chronic hemodialysis, most centers strive for a weekly KTN urea value at or above 3.0 (2), whereas in CAPD the typical regimen yields a weekly KTN urea between 1.5 and 1.8. There was great interest in kinetic modeling of CAPD clearance prescriptions at the 10th Annual Conference on Peritoneal Dialysis in Dallas, Texas, in February of 1990 (1, 3–6). The focus was on defining adequate peritoneal dialysis and optimizing nutrition. The purpose of this editorial is not to review the pros and cons of modeling dialysis therapy to achieve defined doses of small solute clearances nor to support or refute the peak concentration hypothesis.