Phosphate Mass Removal during Hemodialysis: A Comparison between eKT/V-Matched Conventional and Extended Dialysis

Abstract

Background and Objectives: The control of hyperphosphatemia is an unmet need in dialysis care. Compared to conventional hemodialysis (cHD), extended hemodialysis (eHD) appears to more easily control blood phosphate levels in chronically dialyzed patients. Here, we sought to compare eKT/V-matched cHD and eHD procedures in order to quantify the contribution of dialysis prescription and time in the mass removal of phosphate. Methods: Eight stable hemodialysis patients with negligible residual renal function underwent cHD and eHD sessions adjusted to provide the same eKT/V_urea. Total dialysate, total and hourly partial dialysate and blood samples were collected for comparison of mass extraction of urea, creatinine, and phosphate. Results: Mean eKT/V_urea was similar in eHD and cHD (1.30 vs. 1.28, p = nonsignificant). Likewise, mass removal of urea and creatinine during cHD and eHD were not significantly different. Conversely, phosphate mass removal was 40% higher with eHD as compared to cHD (1,219 ± 262 vs. 858 ± 186 mg, p = 0.015). Although hourly mass removal of phosphate was higher during cHD, the prolonged period of lesser but continuous removal was responsible for higher total phosphate elimination during eHD. Conclusion: In dialysis sessions matched to provide a similar eKT/V_urea, removal of phosphate increases by 40% when time is extended from 4 to 8 h. Urea-based adequacy models cannot be used to predict the amount of phosphorus removal during hemodialysis.