(296c) Outside-in Hemodialysis: A Study of Toxin Clearance

For a patient with chronic or acute kidney failure, it is advantageous to perform hemodialysis continuously and for long durations in order to gradually remove excess fluids and improve toxin removal. Unfortunately, such long-term treatments are often hampered by the short lifetimes of the hollow-fiber dialyzers used in toxin removal, which arise due to blood clots formed in these fibers. The blood clots often block an entire fiber, so as more fibers are clogged, the surface area of the dialyzer and waste clearance are drastically lowered.

Labib and Dukhin (Novaflux Inc.) postulated that this clotting limitation can be overcome by a new approach that switches flow on the blood and dialysate side. In the outside-in filtration (OIF) configuration, dialysate flows inside the fibers and blood flows through the inter-fiber space. The researchers showed that OIF would allow prolonged hemodiafiltration with little dialyzer clogging.¹ With OIF, even if small inlet thrombi form that would block fibers in conventional intraluminal blood flow, these clots will have minimal effect on the blood flow and filtrate flux in OIF due to the three-dimensional system of interconnected hydrodynamic flow channels in the inter fiber space. However, very few studies have looked into the impact of OIF on toxin clearance and the level of mass transport of solutes with different sizes. The objective of this study is to experimentally assess the transport of different types of uremic toxins under both outside-in (OIF) and inside-out (standard) configurations. For small solutes, toxin clearance is relatively similar between the OIF configuration and the standard configuration, for both diffusive and convective transport. For larger toxins, however, we observed a noticeable difference in clearance level when OIF mode is used. We will discuss the physical mechanisms behind these observations, and the consequences of these observations for clinical applications.

¹ Dukhin SS, Labib M, et al. Outside-in hemofiltration for prolonged operation without clogging. Journal of Membrane Science 464 (2014).