Background. Recent dialyzer-related developments have concentrated upon the improvement of performance and biocompatibility. The focus of these developments was predominantly on the membrane itself. A newly developed high-flux dialyzer (FX60) with an advanced Fresenius Polysulfone 1 membrane (Helixone 1 ) overcomes this limitation and has several design-related advantages attributed to the redesign of the individual functional components. For the first time, polypropylene was selected as the

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... erial for the dialyzer housing. Both the fibre and the fibrebundle geometry were refined with the aim of improving overall performance and to reduce dialysate consumption. Methods. This study aims at investigating the in vitro and in vivo performance of the new FX60 dialyzer with the focus on dialysate flow distribution and dialysate consumption. A new method to analyse dialysate flow distribution, based on local clearances, is suggested. The effect of reducing dialysate flow from 500 to 300 mlumin is investigated in vivo. Results. K 0 A urea , a common measure to quantify device performance, is found to approach 1000 mlumin for the FX60 with a surface of only 1.4 m 2 . Local clearance measurement shows equal performance of the Helixone 1 fibre bundle over the entire cross-section. A dialysate flow reduction by 20% (in vivo) only results in a minor loss in clearance. Conclusions. The newly developed high-flux dialyzer (FX60) shows a remarkable performance (K 0 A urea ). The excellent utilization of dialysate could be proven in vivo and is attributed to the superior dialysate flow distribution. A reduction of dialysate flow by 20% could lead to substantial economic savings.