BOUND SOLUTE DIALYSIS WITH ULTRAFILTRATION

Abstract

Bound solute dialysis (BSD), as practiced by MARS (“albumin dialysis”) and the Biologic-DT (“sorbent dialysis”), is directed toward removal of protein-bound toxins and has shown some clinical efficacy in treatment of liver failure patients. Semicontinuous ultrafiltration with dialysis (SCUF-D), rather than dialysis, is used to maintain or reduce patient volume. Objective: Understand the impact of ultrafiltration (UF) volume removal from a patient in conjunction with BSD on protein-bound toxin reduction. Methods: A thermodynamically-based engineering model of SCUF-D coupled with BSD (SCUF-BSD) in which the bound toxin, but not the binding protein, can cross the membrane is developed. Four dimensionless ratios (κ; membrane extraction/perfusion rate; α: dialysate/perfusate rate; β: dialysate/perfusate albumin ratio; γ: fractional UF rate) govern the ability of SCUF-BSD to remove albumin-bound solutes from the blood stream. Results: UF of protein-bound toxin removes some toxin mass but leads to an increase in toxin concentration because the binding protein concentration increases with decreasing volume. For any SCUF-BSD UF cartridge, toxin mass removal from a patient is insensitive to α when α >0.2. Toxin mass removal is also insensitive to dialysate albumin concentration once β >0.02. At that point, SCUF-BSD toxin removal doubles in comparison SCUF-D. Also, when β >0.02 bound toxin removal increases with decreasing UF rate, at equivalent volume reduction, because higher UF rates lower the total time available for BSD treatment and it is BSD that promotes bound toxin removal. Conclusion: SCUF-BSD is more efficacious than SCUF-D for bound solute toxin removal.