The Method to Predict Postdialysis Equilibrated Kt/V with Only Intradialytic Urea Samples

Lee, Jong Soo; Kim, Do Ha; Choi, Seung Won; Kim, Young Il; Park, Jae Hoo; Park, Su Kil; Lee, Sang Koo; Lee, Seon Ho; Kim, Sung Ryul; Park, Jung Sik

Abstract

PURPOSE: Postdialysis urea rebound(PDUR) causes the overestimation of actual amount of delivered dialysis in Kt/V from single pool urea kinetic. To correct PDUR and predict equilibrated Kt/V(eKt/V) some methods have suggested by Daugirdas, et al., Smye, et al. and Tattersall, et al. The purposes of this study were to determine the optimum intradialytic urea sample time that fits best with PDUR and to compare calculated Kt/V by this sample with the different other methods.
METHODS
The subjects were 21 patients who were dialyzed at three times 4 hours weekly, using bicarbonate and cellulosynthetic membranes. Blood samples to measure BUN were obtained at initiation of dialysis session and then at 80, 120, 180, 200, 210, 220 minutes, and the end of dialysis session times and then at 45 minutes of postdialysis. We compared four different methods of eKt/V with the equilibrated 45-minute PDUR Kt/V(eKt/V PDUR) as the reference method.
RESULTS
The mean PDUR was 17.2+/-%. spKt/V and eKt/V PDUR was 1.300+/-.24 and 1.120+/-.20 respectively, leading to overestimation of actual delivered Kt/V by 13.5+/-%. The best time for intradialytic sampling to fit with PDUR BUN was 40 minute before the end of session. eKt/V by Daugirdas formulae(eKt/V Dau=1.315+/-.21, r=0.972, p<0.001), Tattersal formulae(eKt/V Tat=1.134+/-.22, r= 0.972, p<0.972, p<0.001) and Smye formulae(eKt/V Smye=1.156+/-.24, r=0.900, p<0.001) showed good correlation with eKt/V PDUR. eKt/V calculated by the sample of 40 minute before end of session(eKt/V T-40=1.120+/-.20, r=0.984) had tendency of the best correlation with eKt/V PDUR. Among these different methods, eKt/V T-40 had the best degree of agreement with eKt/V PDUR by Bland-Altman analysis.
CONCLUSION
Our results suggest that the use of spKt/V is not adequate to estimate the amount of delivered hemodialysis dose because of the existence of significant postdialysis urea rebound even conventional 4 hour dialysis. Intradialytic sampling method is a simple and accurate method to predict eKt/V for use in clinical practice.