Abstract

The technique of dialysis has seen enormous advancements over the past fifty years, evolving from an initial phase,primarily based on diffusion through a semipermeable membrane to the current preference for high-efficiency convection, involving the removal of several liters of ultrafiltrate. Diffusive dialysis, due to its relative simplicity in execution, has allowed the treatment of millions of individuals with ESRD, ensuring them a certain quality of life. However, it is not considered optimal in terms of survival and has some complications inherent to the uremic state. Convection, by removing toxic substances through solvent drag, has enabled the purification of not only small molecules but also medium-to-large molecular weight molecules. As a result, hemodiafiltration techniques have shown improvements in both mortality and intradialytic complications such as cramps and intradialytic hypotension. These results, however, involve fluid exchanges that far exceed 20 liters per session, thus increasing technical complexity and not being applicable to all patients, particularly those with vascular access problems. The recent discovery of so-called medium cut-off (MCO) membranes appears to maintain the benefits of hemodiafiltration techniques without the need for high convective flows. Therefore, the debate between convection and diffusion seems far from over and may hold more surprises in the near future.

Keywords: diffusion, convection, hemodialysis, hemodiafiltration, medium cut-off membranes.