A simple method for the calculation of dialysis Kt factor as a quantitative measure of removal efficiency of uremic retention solutes: Applicability to high-dialysate vs low-dialysate volume technologies.

Dialysis urea removal metrics may not translate into proportional removal efficiency of non-urea solutes. We show that the Kt factor (plasma volume totally cleared of any solutes) differentiates removal efficiency of non-urea solutes in different technologies, and can easily be calculated by instant blood-dialysate collections. We performed mass balances of urea, creatinine, phosphorus and beta2-microglobulin by whole dialysate collection in 4 low-flux and 3 high-flux hemodialysis, 2 high-volume post-hemodiafiltration and 7 short-daily dialysis with the NxStage-One system. Instant dialysate/blood determinations were also performed at different times, and Kt was calculated as the product of the D/P ratio by volume of delivered dialysate plus UF. There were significant differences in single session and weekly Kt (whole dialysate and instant calculations) between methodologies, most notably for creatinine, phosphorus and beta2-microglobulin. Urea Kt messured in balance studies was almost equal to that derived from the usual plasma kinetic model-based Daugirdas' equation (eKt/V) and independent V calculation, indicating full correspondence. Non-urea solute Kt as a fraction of urea Kt (i.e. fractional removal relative to urea) showed significant differences between technologies, indicating non-proportional removal of non-urea solutes and urea. Instant Kt was higher than that in full balances, accounting for concentration disequilibrium between arterial and systemic blood, but measured and calculated quantitative solute removal were equal, as were qualitative Kt comparisons between technologies. Thus, we show that urea metrics may not reliably express removal efficiency of non-urea solutes, as indicated by Kt. Kt can easily be measured without whole dialysate collection, allowing to expand the metrics of dialytic efficiency to almost any non-urea solute removed by dialysis.

Single Session and Weekly Beta 2-Microglobulin Removal with Different Dialytic Procedures: Comparison between High-Flux Standard Bicarbonate Hemodialysis, Post-Dilution Hemodiafiltration, Short Frequent Hemodialysis with NxStage Technology and Automated Peritoneal Dialysis.

BACKGROUND: NxStage System One cycler (NSO) is a widespread system for home daily dialysis. Few data are available on the impact of this "low dialysate volumes system" on the removal rate of poorly diffusible, time-dependent solutes like ß2-microglobulin (ß2M). METHODS: Single-session and weekly balances of ß2M were performed and compared in 12 patients on daily NSO, 13 patients on standard high-flux bicarbonate dialysis (BHD), 5 patients on standard post-dilution on line hemodiafiltration (HDF), and 13 patients on automated peritoneal dialysis (APD). RESULTS: Intradialytic fall of plasma water ß2M levels (corrected for rebound) was 65.2 ± 2.6% in HDF, 49.8 ± 9.1% in BHD, and 32.3 ± 6.4% in NSO (p < 0.001 between all groups). Single treatment dialysate removal was much less in APD (19.4 ± 20.4 mg, p < 0.001) than in any extracorporeal technologies, and was less in NSO (126.2 ± 35.6 mg, p < 0.001) than in BHD (204.9 ± 53.4 mg) and HDF (181.9 ± 37.6 mg), with no differences between the latter 2; however weekly removal was higher in NSO (757.3 ± 213.7 mg, p < 0.04) than in BHD (614.8 ± 160.3 mg) and HDF (545.8 ± 112.8 mg). Extrapolated ß2M adsorption to the membrane was negligible in BHD, 14.7 ± 9.5% of total removal in HDF and 18.3 ± 18.5% in NSO. Integration of single session data into a weekly efficiency indicator (K × t) showed total volume of plasma cleared in NSO (33.4 ± 7.7 L/week) to be higher than in BHD (26.9 ± 7.2 L/week, p < 0.01) and not different than in HDF (36.2 ± 4.7 L/week); it was negligible (3.2 ± 1.0) in APD. CONCLUSIONS: Weekly ß2M removal efficiency proved equal and highest in HDF and NSO (at a 6/week prescription), slightly lesser in BHD and lowest in APD.

Phosphate and Calcium Control in Short Frequent Hemodialysis with the NxStage System One Cycler: Mass Balance Studies and Comparison with Standard Thrice-Weekly Bicarbonate Dialysis.

BACKGROUND: Short frequent dialysis with NxStage System One cycler (NSO) has become increasingly popular as home hemodialysis prescription. Short dialysis sessions with NSO might not allow adequate phosphate (P) removal. METHODS: Single-session and weekly balances of P and calcium (Ca) were compared in 14 patients treated with NSO (6 sessions/week) and in 14 patients on standard bicarbonate dialysis (BHD). RESULTS: NSO and BHD showed similar plasma P fall, with end-dialysis plasma P slightly lower in BHD (2.2 ± 0.5 vs. 2.7 ± 0.8 mg/dL, p < 0.02). Single-session P removal was lower in NSO, but weekly removal was higher (3,488 ± 1,181 mg vs. 2,634 ± 878, p < 0.003). Plasma Ca increase was lower in NSO, with similar PTH fall. Ca balance varied according to start plasma Ca, dialysate to blood Ca gradient and net ultrafiltration. CONCLUSIONS: short, frequent home hemodialysis with NSO, on a 6/week-based prescription, allows higher weekly P removal than BHD. With the dialysate Ca concentration in use (6 mg/dL), total plasma Ca and iCa concentration increase is lower in NSO.