A regenerable potassium and phosphate sorbent system to enhance dialysis efficacy and device portability: a study in awake goats

Background: Patients on standard intermittent haemodialysis suffer from strong fluctuations in plasma potassium and phosphate. Prolonged dialysis with a wearable device, based on continuous regeneration of a small volume of dialysate using ion exchangers, could moderate these fluctuations and offer increased clearance of these electrolytes. We report in vivo results on the efficacy of potassium and phosphate adsorption from a wearable dialysis device. We explore whether equilibration of ion exchangers at physiological Ca2, Mg2 and hypotonic NaCl can prevent calcium/magnesium adsorption and net sodium release, respectively. Effects on pH and HCO- 3 were studied. Methods: Healthy goats were instrumented with a central venous catheterand dialysed. Potassium and phosphate were infused to achieve plasma concentrations commonly observed in dialysis patients. An adsorption cartridge containing 80 g sodium poly(styrene- divinylbenzene) sulphonate and 40 g iron oxide hydroxide beads for potassium and phosphate removal, respectively, was incorporated in a dialysate circuit. Sorbents were equilibrated and regenerated with a solution containing NaCl, CaCl2 and MgCl2. Blood was pumped over a dialyser and dialysate was recirculated over the adsorption cartridge in a countercurrent direction. Results: Potassium and phosphate adsorption was 7.7 6 2.7 and 4.9 6 1.3 mmol in 3 h, respectively. Adsorption capacity remained constant during consecutive dialysis sessions and increased with increasing K and PO3- 4 : Equilibration at physiological Ca2+ and Mg2+ prevented net adsorption, eliminating the need for post-cartridge calcium and magnesium infusion. Equilibration at hypotonic NaCl prevented net sodium release Fe2+ and arterial pH did not change. Bicarbonate was adsorbed, which could be prevented by equilibrating at HCO- 3 : Equilibration at physiological Ca2+ and Mg2+ prevented ne 15mM. Conclusion: We demonstrate clinically relevant, concentrationdependent, pH-neutral potassium and phosphate removal in vivo with small volumes of regenerable ion exchangers in our prototype wearable dialysis device. Application of the selected ion exchangers for potassium and phosphate removal in a wearable dialysis device appears to be effective with a low-risk profile.