Modeling of Internal Filtration in Theranova Hemodialyzers.

High retention onset (HRO) is the designation for a new class of hemodialysis membranes. A unique characteristic of this class is the highly selective and controlled porosity resulting in sieving properties that provide a clinically desirable balance between middle/large molecular weight solute removal and albumin loss. Another defining feature of this membrane class is the relatively small fiber diameter, which produces high convective volumes in the form of internal filtration. The aim of the present study was to estimate, by semi-empirical methods, convective volumes for 2 new HRO dialyzers: Theranova 400 and Theranova 500 (Baxter International Inc., Deerfield, IL, USA). Axial blood and dialysate compartment pressure drop along with transmembrane pressure, measured in vitro with blood (Qb = 300 or 400 mL/min; Qd = 500 mL/min; net ultrafiltration rate = 0), served as input parameters for 3 different models: linear, geometric, and (non-linear) mathematical. Based on the most rigorous mathematical model, the estimated convective volumes were 1,661 mL/h (Qb = 300 mL/min) and 1,911 mL/h (Qb = 400 mL/min) for Theranova 400 and 1,864 mL/h (Qb = 300 mL/min) and 1,978 mL/h (Qb = 400 mL/min) for Theranova 500. These results suggest that the unique fiber characteristics of this new class of membranes provide substantial convective volumes without the need for exogenous substitution fluid. As such, HRO membranes are a major end-stage renal disease treatment advance in the quest to enhance the removal of larger-sized uremic toxins.