Paired filtration dialysis: optimizing depurative efficiency with separate convection and diffusion processes

To overcome reciprocal interaction between convection and diffusion occurring in hemodiafiltration, we separated the two processes in a new dialysis technique called paired filtration dialysis (PFD). In this technique, convection and diffusion take place separately on two capillary membranes: a polysulfone hemofilter and a hemophan dialyzer. The depurative effectiveness of PFD with respect to small (blood urea nitrogen, creatinine, uric acid, phosphate) and large (beta 2-microglobulin) molecules was acutely assessed in 6 patients on maintenance acetate hemodialysis. Despite a 3-hour treatment time, a high mass removal of small and large solutes was found in PFD without high ultrafiltration rates or blood flows in excess of 300 ml/min. There was no significant difference in solute removal between the two different depurative sequences adopted in PFD, i.e., convection followed by diffusion or vice versa. A significant reduction in beta 2-microglobulin serum levels was observed in both PFD modes. Twenty patients, on a 12-month period of 3-hour PFD treatment, maintained an unaltered metabolic, clinical, and acid-base status, and cardiovascular stability was not affected. PFD thus provides excellent depurative results, along with simple technical features that are particularly useful in treating patients with high depurative needs and yet are unable to tolerate high-flux techniques.