How Much Is the Removed Amount of Potassium with On-Line Hemodiafiltration Affected by the Filter Surface?

Introduction: The potassium removed by various dialysis methods (pre- and post-dilution on-line hemodiafiltration) is not clear in the literature. The aim of the study was to investigate the amount of potassium eliminated with each session of pre- or post-dilution on-line hemodiafiltration with collection of the total ultrafiltrate in a tank. Materials and Methods: We studied in 10 dialyzed patients the removal of potassium by a polyetherosulfone dialysis filter. We sought to investigate whether the amount removed is related to filter surface area and type of dialysis. We examined the removal of potassium by on-line hemodiafiltration and post-dilution with high-flux filters, surface areas 2.5 m2 (Group A) and 2.1 m2 (Group B). We repeated the same process with low-flux filters with conventional hemodialysis (Group C), as well as with pre-dilution on-line hemodiafiltration and 2.5 m2 surface area filters (Group D). Results: Significantly higher potassium removal was noted with post-dilution on-line hemodiafiltration versus conventional haemodialysis, which was not affected by filter surface area, and also higher with pre-dilution on-line hemodiafiltration versus all other methods. The amounts of removed potassium even exceeded 300 mmol of potassium/dialysis session in some cases. Conclusions: It is concluded that, with on-line hemodiafiltration, much higher amounts of potassium are removed (mainly with pre-dilution) compared to conventional haemodialysis. The amount removed is not affected by the surface of the filter. The lower potassium levels of dialysate play an important role in this elimination.