Theoretical basis for and improvement of Daugirdas' second generation formula for single-pool Kt/V

Purpose: An empirically-derived equation to estimate hemodialysis treatment variable-volume single-pool Kt/V, where Kt/V = -In(R-GFAC x t) + (4-3.5 x R) x UFV/W, was published in 1993 (1) and quickly became a standard tool for the estimation of dialysis dose. We aim to find a theoretical basis for this equation. Methods: A mathematical derivation is used to find the connection between Kt/V and modeled urea concentrations. Results: There is a theoretical basis for the empirical structure of the estimating equation, but the estimation of the effect of ultrafiltration on Kt/V can be improved. Finally, we show that the accuracy of the formula may be suboptimal for some extreme dialysis schedules and propose a new equation that is more robust across atypical dialysis prescriptions. Conclusions: The currently used Kt/V estimating equation has a sound theoretical basis and an improved version is proposed that can maintain accuracy with a broader range of fluid removal.