Quest for postdialysis urea rebound-equilibrated Kt/V with only intradialytic urea samples

Background. Postdialysis urea rebound (PDUR) is a cause of K-t/V overestima tion when it is calculated from predialysis and the immediate postdialysis blood urea collections. R Measuring PDUR requires a 30- or 60-minute postdi alysis sampling, which is inconvenient. Several methods had been devised fo r a reasonable approach to determine PDUR-equilibrated K-t/V in short dialy sis without the need for a delayed sample. The aim of our study was to comp are these different K-t/V methods during the longer eight-hour hemodialysis sessions, and to determine the optimum intradialytic urea sample time that fits best with PDUR. Methods. The study included 21 patients (mean age 71.9 years) who: Were hem odialyzed for 60+/- 60 months at three times eight hours weekly, using bica rbonate dialysate and cellulosic membranes. Blood urea samples were obtaine d at onset, and then at 17, 33, 50, 66. 75, 80, 85, and 100% of the dialysi s session times. after 30 seconds of low flow, and then at 60-minutes postd ialysis. All patients had a meal during dialysis. We compared four differen t formulas of K-t/V [(a) K-t/V-Smye with a 33% dialysis time urea sample, ( b) two-pool equilibrated eK(t)/V, (c) K-t/V-std (Daugirdas-2) obtained with an immediate postdialytic sample, and (d) the different intradialytic urea samples for I;K-t/V (50, 66, 75, 80, and 85% of dialysis time)] with the e quilibrated 60-minute PDUR K-t/V (K-t/V-r-60) formula as the reference meth od. Results. The mean PDUR was 17.2 +/- 9%, leading to an overestimation of K-t /V-std by 12.2%. Kt/V-r-60 was 1.68 +/- 0.34. I;K-t/V-std was 1.88 +/- 0.36 (Delta = 12.2 +/- 4.8%, r = 0.8). eK(t)/V was 1.77 0.3 (Delta = 5 +/- 5%, r = 0.96), and K-t/V-Smye was 1.79 +/- 0.47 (il = 5.2 +/- 14%, i = 0.9). Th e best time for the intradialytic sampling was 80% (that is, at 6 hr and 24 min). The Rt,K-t/V-80 was 1.64 +/- 0.3 and was best fitted with K-t/V-r-60 (Delta = -1.8 +/- 8%, r = 0.91). The mean intradialytic urea evolution sho wed a three-exponential rate, in discrepancy with the: two-exponential rate theoretical model. Conclusions. These results confirm that a significant postdialysis rebound exists in an eight-hour dialysis. An intradialytic urea sample taken at 80% of the total session time permits an estimation of the 60-minute K-t/V-reb ound without the necessity of taking a delayed sampler with better accuracy than eK(t)/V or especially Kt/V-Smye. This may be related to a particular urea kinetics curve on the longer dialysis duration, which needs to be stud ied further.