UREA CONCENTRATION GRADIENTS DURING CONVENTIONAL HEMODIALYSIS

To elucidate the intradialytic urea concentration gradients, we examin ed 26 hemodialysis patients wearing a double-lumen central venous cath eter during their first or second fistula-punctured dialysis session. In 17 patients (group A), after 60 and 240 minutes of treatment with a mean blood flow of 196.4 +/- 9.9 mL/min, blood urea nitrogen (BUN) wa s measured in blood samples taken simultaneously from the central veno us catheter, a vein in the arm opposite the access site, and the arter ial and venous lines of the dialyzer. In 16 patients (group B), after 60 minutes of treatment with a mean blood flow rate of 197.5 +/- 12.3 mL/min, BUN was measured in blood samples taken from the dialyzer arte rial line and then, after decreasing the blood flow to 50 to 60 mL/min for 1 minute, in samples taken from a vein in the arm opposite the ac cess site, the central venous catheter, and the dialyzer arterial line . In group A, the mean BUN values in the dialyzer arterial line at 60 and 240 minutes were found to be 3.7% +/- 3.7% and 3.5% +/- 3.4% highe r than the corresponding values in the central veins, respectively (P = NS between 60 and 240 minutes). In group B, after 1 minute of low bl ood flow, this difference was 1.5% +/- 2.4% (P = 0.06 compared with gr oup A). The peripheral veins in group A patients at 60 and 240 minutes had 9.%7 +/- 5.2% and 10.9% +/- 5.3% higher BUN values, respectively, compared with the central veins. This difference in group B patients after 1 minute of low blood flow was 6.8% +/- 4.2%. Urea access recirc ulation rate in group A, calculated by the classical three-samples met hod, was found to be 7.6% +/- 5.0% at 60 minutes and 9.9% +/- 5.8% at 240 minutes (P = NS). In group B, BUN values in the dialyzer arterial line after 1 minute of low blood flow increased significantly by 3.4% +/- 4.5% (P < 0.01). Our study shows that during conventional hemodial ysis with a blood flow rate of 200 mL/min, urea concentration in the c entral veins is lower than in the dialyzer arterial line. This gradien t after 1 minute of low-flow dialysis had a tendency to decrease. At t he same time, however, the urea concentration gradient between the per ipheral and central veins remained high, indicating that during conven tional hemodialysis, intercompartmental disequilibrium plays a signifi cant role in the arteriovenous gradient. (C) 1996 by the National Foun dation, Inc.