The availability of hemodialysis machines equipped with online clearance monitoring (OCM) allows frequent assessment of dialysis efficiency and adequacy without the need for blood samples. Accurate estimation of the urea distribution volume (V) is required for Kt/V calculated from OCM to be consistent with conventional blood sample-based methods. A total of 35 patients were studied. Ionic dialysance was measured by conductivity monitoring. The second-generation Daugirdas formula was used to calculate the Kt/V single-pool (Kt/VD). Values of V to allow comparison between OCM and blood-based Kt/V were determined using Watson formula (VWa), bioimpedance spectroscopy (Vimp), and blood-based kinetic data (Vukm). Comparison of Kt/Vw ocm calculated by the ionic dialysance and Vw (Kt/Vw ocm) with Kt/VD shows that using VW leads to significant systematic underestimation of dialysis dose by 24%. Better agreement between Kt/V ocm and Kt/VD was observed when using Vimp and Vukm. Bio-impedancemetry and the indirect method using the second-generation Daugirdas equation are two methods of clinical interest for estimating V to ensure greater agreement between OCM and blood-based Kt/V.

Diffusive clearance depends on blood (Qb) and dialysate flow (Qd) rates and the overall mass transfer area coefficient (KoA) of the dialyzer. In this article we describe a model to predict an appropriated AutoFlow (AF) factor (AF factor = Ratio Qd/Qb), that is able to provide adequate Kt/V for hemodialysis patients (HDP), while consuming lower amounts of dialysate, water and energy during the treatment. We studied in vivo the effects of three various Qd on the delivered dose of dialysis in 33 stable HDP. Hemodialysis was performed at Qd of 700 mL/mn, 500 mL/mn, and with AF, whereas specific dialysis prescriptions (treatment time, blood flow rate [Qb], and type and size of dialyzer) were kept constant. The results showed that increasing the dialysate flow rate more than the model of AF predicted had a small effect on the delivered dose of dialysis. The Kt/V (mean ± SD) was 1.52 ± 0.16 at Qd 700, 1.50 ± 0.16 at Qd 500, and 1.49 ± 0.15 with AF. The use of the AF function leads to a significant saving of dialysate fluid. The model predicts the appropriate AF factor that automatically adjusts the dialysate flow rate according to the effective blood flow rate of the patient to achieve an appreciable increase in dialysis dose at the lowest additional cost.

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