Calcium mass transfer with 10-hour dwell time using 1.25 versus 1.75 mmol/L calcium dialysate

Dialysate containing 1.25 mmol/L calcium and 2.5 g/dL dextrose has been shown to have a negative calcium mass transfer (CMT) in a 4-hour exchange. Continuous ambulatory peritoneal dialysis (CAPD) patients usually perform three daytime exchanges that have short dwell times and one overnight exchange that dwells for 8-10 hours. Measurement of CMT with a 10-hour overnight CAPD exchange has not been done. Thirty-four CMT measurements were performed on 18 patients using 1.25 (n = 15) and 1.75 mmol/L (n = 19) calcium dialysate, both containing 2.5 g/dL dextrose, with a dwell time of 10 hours. The mean CMT values were -0.75 +/- 0.45 and 0.42 +/- 0.54 mmol/exchange for 1.25 and 1.75 mmol/L calcium dialysate, respectively (p < 0.001). The serum ionized calcium levels were similar in the two groups, 1.2 mmol/L. With multivariate analysis the CMT values had a negative correlation with drain volumes (r = -0.5, p = 0.0001) and serum-ionized calcium (r = -0.4, p = 0.002). In conclusion, the CMT of an overnight exchange using 2.5 g/dL dextrose is determined by the initial dialysate calcium, the ultrafiltration volume, and the serum-ionized calcium. An overnight dwell using 1.25 mmol/L calcium dialysate will contribute to negative calcium balance, allowing larger doses of oral calcium compounds to be prescribed.