SCREENING FOR EXTREME POSTDIALYSIS UREA REBOUND USING THE SMYE METHOD- PATIENTS WITH ACCESS RECIRCULATION IDENTIFIED WHEN A SLOW FLOW METHOD IS NOT USED TO DRAW THE POSTDIALYSIS BLOOD

To look for patients with extreme urea rebound, we drew intradialytic samples one third of the way into dialysis during routine modeling for 3 months. The samples taken postdialysis were obtained after stopping the blood pump, without any slow flow period. Using the Smye equation s, the intradialytic urea level was used to predict urea rebound, expr essed as Kt/V-equilibrated minus Kt/V-single pool (Delta Kt/V). Result s were averaged for the 3-month period in 369 patients. Mean estimated Delta Kt/V was -0.20 +/- 0.13, which was similar to but slightly high er than the predicted value (-0.6 X K/V + 0.03) of -0.19 +/- 0.04. In 27 patients, extreme rebound (mean Delta Kt/V < -0.40) was found. Sixt een of these patients consented to further study, but only after acces s revision in four patients. In these patients, additional slow flow s amples after 15 seconds and 2 minutes of slow flow, respectively, were drawn one third of the way into dialysis and postdialysis, and a samp le was drawn 30 minutes after dialysis. On restudy, postdialysis rebou nd was still high with full flow samples Delta Kt/V = -0.40 +/- 25, bu t was much lower (-0.18 +/- 0.07) and similar to predicted rebound (-0 .19 +/- 0.05; P = NS) when based on 15-second slow flow samples. Eight of the 16 had marked (>15%) access recirculation by urea sampling, an d Delta Kt/V based an full flow post samples correlated with access re circulation (r = -0.91). The results suggest that the Smye method is v aluable for identifying patients with aberrantly large postdialysis re bound values. When the postdialysis samples are drawn without an antec edent slow flow period, most patients with extreme rebound values turn out to have marked access recirculation. (C) 1996 by the National Kid ney Foundation, Inc.