Calcium and magnesium flux in automated peritoneal dialysis

Background: Calcium and magnesium balance in continuous ambulatory peritoneal dialysis (CAPD) has been extensively studied with several of the different formulations of fluid available. Calcium and magnesium balance in automated PD (APD) is less well studied and the effect on Ca and Mg flux is unknown. Data on glucose polymer solutions are also lacking. This prospective observational study was undertaken to examine mass transfer of Ca and Mg in APD patients. Methods: 12 patients on APD were studied for two 24-hour periods using, alternately, 1.75 mmol/L and 1.25 mmol/L Ca (Dianeal PD1 and Dianeal PD4; Baxter Healthcare, Newbury, UK) 1.36% glucose-based dialysis fluid for the 9-hour overnight dialysis, followed by a 15-hour daytime dwell of glucose polymer-based fluid (icodextrin). Serum ionized Ca, serum Mg, and dialysate Ca and Mg concentrations were measured at the beginning and end of each period. Mass transfer was calculated as millimoles per exchange. Results: During rapid overnight exchanges with Dianeal PD1 and PD4, mass transfer of Mg and Ca did not show significant correlations with serum levels when using PD1 fluid; however, mass transfer of Mg, but not Ca, was significantly correlated to serum levels when using PD4 fluid. During the long dwell with icodextrin, dialysate drain volume was the most significant factor determining the flux of both Ca and Mg. Conclusion: Mass transfer of Ca and Mg in APD patients using conventional dialysis fluid was not related to drain volume in this study, which differs to studies in CAPD. Flux of Ca and Mg during icodextrin use was found to be dependent on ultrafiltration rate and not dialysate or serum concentration. © 2009 International Society for Peritoneal Dialysis.