TOP7: Dialy-ssist: A Complementary Dialysate Recycling System for Dialysate and Water conservation

Abstract

Background: Hemodialysis (HD) is the dominant form of blood purification employed for patients with end-stage renal disease. Operationally, present HD systems utilize a hollow fiber kidney system in which blood is perfused thru while dialysate is cross-perfused over and surrounding the fiber bundle allowing for fluid, electrolyte and waste exchange, with equilibration based on the tonicity and ion concentration of the dialysate. Unfortunately, present systems require access to a large source of water and dialysate, are hospital or clinic-based, and non-portable. Here we examined the possibility of creating a system – “Dialy-ssist” to recapture dialysate and water, to allow for its reuse. Our long-term goal is to develop a system which has applicability to both hospital/clinic systems as well as for evolving home portable systems, freeing up the dependence and use of significant water supplies. As a first step here, we modeled the exchange efficiency needed for a dialysate recycling and water conservation system. Methods: A system was designed that utilizes activated charcoal, urease, zirconium oxide, and zirconium phosphate (Dialy-ssist). In silico modeling was performed to determine the optimal amount of activated charcoal, urease, hydroxyl zirconium oxide, and zirconium phosphate needed for removal of urea and ions such as Na+, Ca2+, Mg2+, K+, and Cl-. Wet in vitro confirmatory experiments were also defined. For these, effluent dialysate collected from a hospital hemodialysis system is run through the Dialy-ssist system for 4 hours, with samples taken hourly for analyte analysis and water purity assessment. Serial recycled dialysate will be compared to fresh utilized control. Results:In silico modeling revealed that for activated charcoal one ounce of activated charcoal will remove 90% or more of chloride, sodium, and potassium ions in the dialysate via perfusion through the system at 100 to 200 mL/min. Based on peer reviewed reaction kinetics for urea decomposition via urease, five grams of urease with excess zirconium oxide and zirconium phosphate is modeled to remove at least 30.4 mmol/L of urea, ~95%. Conclusion: Modeling of dialysate recycling via the Dialy-ssist system demonstrates its ability to adequately remove contaminants and achieve a purity level acceptable for clinical reuse. Salts and urea can be removed from the fluid with up to 90% efficiency allowing up to 3 cycles of recuse. Modeling also reveals that the system can conserve 36 – 108 liters of water. In vitro wet studies are ongoing to confirm and refine the efficacy of this system to advance it towards the clinic. Experiments will reveal solute actual removal rate compared to theoretical predictions. Samples collected over time will define the real lifespan of filters and sorbents of this system.