Blood-Membrane Interactions During Dialysis

In extracorporeal renal replacement therapies, the dialyzer is not only the site at which solute removal occurs but also the extracorporeal circuit component having the largest surface area exposed to blood. Therefore, it is not surprising that interactions between blood components and the dialyzer membrane influence the dialysis procedure in several ways. Based on engineering principles, fluid flow along a surface such as membrane results in the development of a boundary layer which can influence solute removal. Furthermore, the exposure of blood to any extracorporeal artificial surface results in the activation of several pathways within the body, including those involving coagulation and complement activation. One of the byproducts of this generalized activation process is protein adsorption to the membrane surface, another phenomenon which can have a significant impact on solute removal. In this article, a detailed review of the ways in which blood-membrane interactions influence solute removal during hemodialysis and related therapies is provided. The influences of secondary membrane formation and boundary layer/concentration polarization effects on solute removal are specifically discussed. Furthermore, the importance of adsorption as a specific removal mechanism for low-molecular weight proteins by highly permeable synthetic membranes is highlighted.