UREA REBOUND - INFLUENCE OF UREA VOLUME D ISTRIBUTION, DIALYZER CLEARANCE AND HEMODIALYSIS TIME

Rapid removal of urea from plasma during hemodialysis creates intercom partmental imbalances followed immediately after dialysis by urea rebo und as an expression of intercompartmental reequilibration. In the pre sent study we have calculated urea rebound and evaluated the influence of the urea volume distribution, dialyzer clearance and hemodialysis time on the urea rebound. 32 patients were included in this study, 17 males and 15 females. Hemodialysis was performed with blood flow 350 m l/mn, ultrafiltration 1,5 l/h, 1.5 m2 cuprophane dialyzer and bicarbon ate buffer. Every patient received 3 dialysis sessions changing dialys is time (1, 2 or 3 hours). A subgroup of 18 patients received 3 aditio nal sessions with blood flow 250 ml/mn and a 1 m2 cuprophane dialyzer. Plasma urea concentration at the beginning, at the end and 45 minutes postdialysis were measured. All dialysate was collected and urea conc entration measured. Urea rebound, urea volume distribution, dialyzer c learance and KT/V were calculated. Urea rebound varied between 9 and 2 6 %, mean 17,0 +/- 3,9 % and no differences were found when dialysis t ime was changed, 15,6 +/- 3,5 % after one hour dialysis, 17,7+/-4,2 % after two hours, and 17,0 +/- 4,0 % after three hours. Linear regressi on analysis showed that urea rebound was correlated with the urea volu me distribution, and the KT/V, and it was not correlated with dialyzer clearance. Significant differences were found in urea rebound among t he two subgroups compared, 10,3 +/- 2,6 % after dialysis with 1 m2 mem brane versus 17,2 +/- 3,4 after dialysis with 1,5 m2 membrane. In conc lusion, our results suggest that individual differences in urea reboun d could be explained by individual variations in urea distribution vol ume. Urea rebound is not influenced by dialysis time, but it is relate d to the dialysis efficiency.