Evaluation and prediction of urea rebound and equilibrated Kt V in the pediatric hemodialysis population

The posthemodialysis blood urea nitrogen (BUN) concentration rebounds for 30 to 60 minutes after hemodialysis in adults. Timing of the posttreatment BUN sample has a significant impact on the calculation of Kt/V. Urea rebound and its effect on Kt/V have not been extensively studied in children and adolescents. We evaluated posthemodialysis urea rebound after 46 treatments in 18 pediatric patients with end-stage renal disease. BUN levels were drawn at 30 seconds and 5 and 15 minutes posttreatment From these values, a logarithmic regression curve was derived that defined percentage of urea rebound (%UR) = -0.254 + 10.9*log(t), (r = 0.79). Using this equation, we estimated BUN, %UR, and Kt/V at equilibration (50 minutes) for each treatment. Estimated mean %UR was 18.7%. Single-pool Kt/V (spKt/V) and estimated double-pool Kt/V (estKt/V) values were significantly different (P < 0.0001). %UR and percentage of difference between spKt/V and estKt/V did not vary as a function of dry weight, body surface area, or K/V. To test the validity of logarithmic extrapolation, additional BUN levels were drawn at 30 seconds and every 10 minutes for 1 hour postdialysis in six patients. Percentage of difference between estKt/V and measured equilibrated Kt/V was 3.6% +/- 1.7%. Our results show %UR has a significant impact on the calculation of KW in children, does not vary with patient size, and is similar to that seen in adults. We have devised an easy and accurate method to predict equilibrated BUN and calculate double-pool Kt/V in children, which requires only an additional 15-minute posttreatment BUN sample. (C) 1999 by the National Kidney Foundation, Inc.