Dialysis Membranes and Hemodialyzers

Hemodialysis and related extracorporeal therapies utilize filters (dialyzers) comprising hollow fiber membranes to achieve solute and water removal. While membrane classification schemes based on composition and water permeability are the historical standard, recent membrane advances have created new perspectives. In particular, the introduction of medium cut-off membranes with mean pore sizes substantially larger than those typical of standard highly permeable membranes for a new therapy (expanded hemodialysis [HDx]) necessitates the development of refined schemes that clearly define the new options available to clinicians. These new approaches will be highlighted along with the interaction between membrane pore size, water permeability, and convective large molecule clearance through the mechanism of internal filtration. The broader molecular weight removal spectrum made possible by these larger pore membranes in HDx will be presented in the context of on-line hemodiafiltration (OL-HDF), both of which rely almost exclusively on convection for large molecule clearance. Finally, the ongoing debate about the appropriate balance between large solute clearance and albumin loss for both HDx and OL-HDF is discussed.