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 overestimation when it is calculated from predialysis and the immediate postdialysis blood urea collections. R Measuring PDUR requires a 30- or 60-minute postdialysis sampling, which is inconvenient. Several methods had been devised for a reasonable approach to determine PDUR-equilibrated K-t/V in short dialysis without the need for a delayed sample. The aim of our study was to compare 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 hemodialyzed for 60+/- 60 months at three times eight hours weekly, using bicarbonate dialysate and cellulosic membranes. Blood urea samples were obtained at onset, and then at 17, 33, 50, 66. 75, 80, 85, and 100% of the dialysis session times. after 30 seconds of low flow, and then at 60-minutes postdialysis. All patients had a meal during dialysis. We compared four different 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 equilibrated 60-minute PDUR K-t/V (K-t/V-r-60) formula as the reference method. 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). The 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 showed 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-rebound 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 studied further.