CARL KJELLSTRAND

The session “Measure of Optimal Dialysis: Theoretical Indications and Implications for Prescriptions” centered on the problem of defining and quantifying delivery of hemodialysis. Zbylut J. Twardowski, MD, University of Missouri, Columbia, Missouri, led off showing data from a study performed in the early 1970s while he was still in Bytom, Poland. The purpose was to see what was better for “adequate dialysis”; increasing the dialysis time per week or increasing the dialysis frequency. Dr. Twardowski studied 14 patients divided into two groups. In a group of 8 patients he kept the dialysis time per week constant (thus keeping the Kt/V essentially unchanged), but added one more dialysis treatment per week, going from three- to four-times weekly dialysis. In the other group, he increased the dialysis time of each session by 17.5%, but kept the number of sessions per week unchanged. The added time would lead to a corresponding increase in Kt/V. The two groups were followed for an average of 6.4 and 6.9 months respectively. Hematocrit, albumin, dry weight, nerve conduction, and blood pressure improved in both groups, but all of these factors improved more in the increased-frequency-and-unchanged-time group, than in the increased-time-of-dialysis-session (and Kt/V) group. This simple but ingenious empirical study clearly showed that more frequent dialysis is better than longer dialysis. It set the stage for the five speakers who followed.

Rod Kenley, from Aksys, Ltd., Libertyville, Illinois, presented the time-averaged deviation (TAD) approach to quantify more frequent dialysis. TAD measures the areas of the urea curve around the weekly mean urea concentration or time-averaged concentration (TAC). He used data from a recently completed six-center study comparing regular three-times weekly dialysis to six-times per week dialysis while keeping weekly dialysis time rigorously constant. While TAC remained essentially unchanged, TAD during six-times weekly hemodialysis was only 70% of that during three-times per week dialysis. He also referenced several studies of daily dialysis showing the remarkable clinical improvement in hematology, blood pressure, nutrition, well-being, and dialysis tolerance that followed the change to daily hemodialysis, even when weekly Kt/V decreased markedly.

Frank Gotch, MD, from Davies Medical Center, San Francisco, California, reviewed the Kt/V concept and pointed out that a malnourished patient with insufficient dialysis, can have the same predialysis blood urea nitrogen, TAD, and TAC as a well nourished, well dialyzed patient. His suggestion was that with thrice-weekly hemodialysis, an equilibrated Kt/V (eKt/V) of over 1.05, and a normalized protein catabolic rate of over 1.0 provide the best definition of adequacy. For other treatment schedules such as daily dialysis, he claimed that the new concept, StdKt/V (transformation of intermittent clearances to an equivalent standard continuous clearance), would provide a better dose parameter to correlate with clinical outcome.

John Daugirdas, MD, from VA Westside Medical Center, Chicago, Illinois, discussed the effect of urea reduction ratio (URR) on single-pool modeled urea distribution volume and the implications for prescription in daily dialysis. The apparent volume of urea distribution shrinks if a single-pool model of urea kinetics is used. In short daily dialysis with a URR of 40% – 50%, the apparent shrinkage in the single-pool modeled volume is 10% – 20%. This can be adjusted for by an equation developed by Daugirdas and Smye (Kidney International 1997; 51:1270–1273).

John Van Stone, MD, University of Missouri, and Dialysis Clinic, Inc., Columbia, Missouri, maintained that peak concentrations of urea and other toxic solutes are enough to judge dialysis adequacy. He argued that for many substances, such as aminoglycosides, toxicity is related to peak concentrations, not average concentrations. If toxicity of urea and other uremic toxins is related to peak, not average, concentrations, then the paradox of clinically adequate CAPD at Kt/V levels that are grossly inadequate for hemodialysis, is resolved. The TAC in continuous dialysis equals the peak concentration in intermittent therapy. The more frequent the intermittent hemodialysis is, the lower the peaks will be, and the closer they will be to the time-averaged value, where the peak value is similar to the average value.

Finally, Thomas Depner, MD, Davis Medical Center, Sacramento, California, argued for direct dialysis quantification and showed some examples using the dialysate urea monitor, Biostat^®.

The Biostat^® continuously measures urea concentration in the spent dialysate as it flows past the probe, integrating the area under the curve. This method allows calculation of the dialysis dose directly, with fewer assumptions than the Kt/V method, and does not require routine measurements of postdialysis BUN. The direct quantification compares the amount of urea removed during dialysis to the amount of urea present in the patient total body water at the start of dialysis.

Carl Kjellstrand, MD, PhD, Aksys, Ltd. Libertyville, Illinois, and Loyola University, Chicago, Illinois, moderated an animated discussion that involved audience participation. There was little doubt that the best performance measure has not yet been developed.