A study of the basic principles determining the performance of several high-flux dialyzers

The clearance characteristics of several commercially available high-flux dialyzers made from cellulose acetate, polyacrylonitrile, polysulphone, and polymethylmethacrylate were studied in vivo. The impact of increasing surface area and adding ultrafiltration on the clearances of small- and larger-molecular-weight species was assessed. The results show there are major differences in large-molecular-weight substance substance handling by different dialyzers as shown by differences in beta 2-microglobulin clearance, independent of ultrafiltration capacity. Membranes made from similar material, eg, Asahi's PAN and Hospal's AN-69 membrane, both made from polyacrylonitrile, differ significantly in their beta 2-microglobulin clearance. Increased surface area results in much greater increase in large-molecular-weight substance clearance. The present study clearly demonstrates that high water flux is not related to high large-molecular-weight permeability. Decisions with respect to impact on dialysis must be based on a knowledge of both the large- and small-molecular-weight permeabilities of the various membranes.