[Comparison of dialyzers in on-line hemodiafiltration]

At present we have a great variety of high-flux dialyzers whose characteristics in vitro seem similar. On-line HDF is a technique which combines diffusion with elevated convection and uses dialysate as replacement fluid. On-line HDF provides the highest clearances for small, medium-sized and large molecules and gives the best performance from the dialyzers. Conscious of this wide choice of dialyzers we evaluated the performance of different dialyzers in renowing small and medium-large molecules. Eleven patients were included in this study, 7 males and 4 females. Every patient received 11 on-line HDF sessions with Fresenius 4008B machine, Qi 100 ml/min or 6 L/h, QB 400 ml/min, QB 800 ml/min, UF 0.5 L/h and Td 60 min. Only the dialyzer was changed: 1.9 m2 cellulose triacetate (Tricea 190G), 2.1 m2 poly methyl methacrylate of PMMA (BK-2.1P), 1.8 m2 polyester-polymer Allol or PEPA (FLX-18GWS), 2.05 m2 acrylonitrile (Filtral 20), 2.1 m2 polyamide (Poliflux 2.1) and 1.8-2.4 m2 polysulfones (HF 80, BS-1.8S, APS-900, Arylane H9, Idemsa 2000, HdF 100). Arterial pressure, venous pressure and transmembrane pressure (TMP) were monitored. Plasma, urea, creatinine, phosphate, uric acid and beta 2m concentrations were measured at the beginning and at the end dialysis from arterial and venous blood lines, and arterial blood line with the slow flow method. Recirculation, dialyzer solutes clearance and solute reduction rates were calculated. No significant differences were found in arterial pressure, venous pressure and recirculation. Small molecule removal was similar except in BK-2.1P and HdF 100 dialyzers which were lower and higher respectively. There were differences in TMP and beta 2m removal among dialyzers employed. Mean TMP, beta 2m clearance and beta 2m reduction ratio were: Tricea 190G (TMP 336 mmHg, beta 2m K 79 ml/min and beta 2m reduction ratio 44.9%), BK-2.1P (TMP 485, beta 2m K 102 and beta 2mRR 48.3%), FLX-18 GWS (TMP 195, beta 2m K 140 and beta 2mRR 54.6%), Filtral 20 (TMP 245, beta 2m K 132 and beta 2mRR 54.1%), Poliflux 2.1 (TMP 209, beta 2m K 158 and beta 2mRR 56.0%), HF 80 (TMP 208, beta 2m K 160 and beta 2mRR 57.4%), BS-1.8S (TMP 186, beta 2m K 179 and beta 2mRR 59.6%), APS-900 (TMP 174, beta 2m K 176 and beta 2mRR 64.8%), Arylane H9 (TMP 206, beta 2m K 171 and beta 2mRR 59.9%), Idemsa 2000 (TMP 203, beta 2m K 169 and beta 2mRR 60.4%), HdF 100 (TMP 152, beta 2m K 186 and beta 2mRR 64.6%).

Of the dialyzers evaluated in on-line HDF, cellulose triacetate and PMMA have a smaller beta 2m removal and their use is limited by an elevated TMP. The polysulfones provide greater beta 2m removal with lower TMP, particularly the APS-900 and HdF 100 dialyzers. The acrylonitrile, PEPA and polyamide are intermediate.