Enhancing filtration rates by the use of blood flow around the capillaries of plasmafilters: an in vitro study.

As the low clearance rate of plasmaseparation limits its use in the treatment of patients suffering from liver failure, sepsis or MOF, we intend to develop strategies for a plasmaseparation unit which increases plasmafiltration rates. Our first question focused on whether commercially available plasmaseparation filters, and in particular their membranes, are suitable for the inversion of blood and plasma compartments. This experimental study was performed using in vitro systems. Commercially available plasmafilters PF2000N (Gambro) and Plasmaflo (Asahi) were compared in both their normal operating mode with blood flow through the capillary lumen, and in the inverse mode. Inverse mode means that blood flows through the outer space of the capillaries while plasma was obtained from the lumen. Heparinised porcine blood (5 I.U./ml) was used in a heated, recirculating in vitro circuit. Our main results were that the normal use of both filter types Plasmaflo and PF2000N enabled maximal blood flows (Qb) of 200 ml/min and filtration rates (Qf) of 25-40 ml/min. Operating the filters in the inverse mode enabled Qb up to 500 ml/min and Qf up to 100 ml/min. Hemolysis, platelet counts and coagulation parameters did not differ significantly regardless of whether the normal or inverse mode was used. The tested plasmafiltration membranes appear to be suitable for use in inverse mode. Although in our experiments, hemocompatibility tests did not indicate severe problems induced by the module geometry, the development of a module specially constructed for blood flow outside of the hollow fibers appears to be necessary in order to minimise shunts and low perfusion areas.