Impact of convective flow on phosphorus removal in maintenance hemodialysis patients

Objective: Hyperphosphatemia leads to increased risk of death in maintenance hemodialysis patients (MHD). This study investigated phosphorus (P) removal, P reduction rate (PRR), and P rebound, comparing on-line, high-volume hemodiafiltration in postdilution (HDF) and high-flux hemodialysis (HD) in a setting of an equal amount of produced dialysate solution in both modalities. Methods: A total of 22 MHD patients, treated with regular 3 X 4 hours HDF weekly, were randomly dialyzed with one 4-hour session of HDF and of HID. In both modalities, an equal amount of produced dialysate solution of 800 mL/minute was used. The only variable was the fact that in HDF, 100 mL/min of this produced dialysate solution was used as replacement fluid. The other parameters were kept identical: blood flow rate, 350 mL/min; high-flux polysulfone F80 dialyzer; and 4800 E monitor, (Fresenius, Bad Homburg, Germany). The P removal was measured in total spent dialysate and ultrafiltrate volumes. Statistical analyses were done with the paired t-test. Results: The mean total P removed with HDF was 1159 +/- 296 mg, and 972 +/- 312 mg with HD (P < .001), ie, 19% higher in HDF; PRR was significantly higher in HDF (63.3%) versus HID (58.6%) (P = .014). The mean serum P did not differ: 5.3 mg/dL in HDF and 5.2 mg/dL in HID. There was a linear correlation between serum P and P removal. With a serum P level up to 5 to 5.5 mg/dL, HIDF achieved a higher P removal compared with HID. The difference gradually decreased as the serum P value increased. Above 7 mg/dL, no difference in total P removal was observed. There was a high but equal rebound percentage at 60 minutes in HIDF (42%) and HD (39%) (P = .42). With HIDF, no predialysis metabolic acidosis was noted. Conclusions: Treatment with on-line HDF in postdilution resulted in a higher P removal and higher PRR compared with HD. The long-term implementation of this modality may result in a more optimal serum P control, without an increase in the number of or lengthening of the dialysis sessions. (c) 2006 by the National Kidney Foundation, Inc.