The importance of convective transport.

Background: Despite technological advances in dialysis equipment and modalities, survival, morbidity, and quality of life of hemodialysis patients are still severely affected by acute intradialytic and long-term complications, possibly related to the treatment itself. Convective treatments, such as high-flux hemodialysis, hemodiafiltration, and hemofiltration are increasingly suggested as further improvements over standard diffusive hemodialysis. The membranes used for these techniques are high-flux semisynthetic and synthetic membranes. Characteristics of these membranes are high permeability, which allows convective removal of water and electrolytes and higher clearance of middle and large molecular weight solutes, and high biocompatibility, which minimizes the "inflammatory response" secondary to interactions between blood and the artificial material of the hemodialysis system.

Methods: With the specific aim of verifying the superiority of convective treatments in reducing morbidity and mortality, we performed a review of the published literature.

Results: Some epidemiological studies suggest that convective treatments reduce morbidity and mortality among dialysis patients. However, the results of the published prospective randomized controlled trials are conflicting. Moreover, since convective treatments are usually performed with synthetic biocompatible membranes, it is hard to separate the effect of convection from the effect of biocompatibility.

Conclusions: To finally assess the effect of high-flux membranes on morbidity and mortality, the results of two randomized, controlled clinical trials (HEMO study and MPO study) specifically designed with this aim are needed.