Are convective methods superior to diffusive dialytic methods?

The principle of convective elimination is the passage of solutes through the membrane carried by water flux, so the elimination of all substances for which membrane is permeable is equal to water. This results in uniform clearances of small, medium and large molecules. Dialytic methods with exclusive or considerable convective elimination are hemofiltration, hemodiafiltration and high-flux hemodialysis. Only by convective methods, middle (MM 300-15,000 D) and large molecules (MM > 1-15,000 D) are cleared. Standard low-flux hemodialysis does not eliminate a considerable amount of medium and large molecules, in contrast to outstanding efficiency in small molecule removal. Clinical significance of larger molecule removal was analyzed in 4 studies prominent for a great number of patients included, very long observation times, or prospective, multicentric randomized design. In 3 studies, dialytic methods with convective elimination were connected with a mortality decrease by 10% to 39% (statistically significant in 2 studies). Dialysis amyloidosis morbidity was lowered by 42%-50% when convective methods were used. Results of the presented studies support the conclusion that dialytic methods with convective elimination are beneficial for survival and prevention of dialysis amyloidosis, irrespective of the biochemical characteristics and complement activation by the membrane used.