Calcium Balance with Automated Peritoneal Dialysis

Background

Calcium balance in chronic kidney disease patients on peritoneal dialysis (PD) has not been well studied. This issue is particularly important, given the careful attention now being paid to vascular calcification, the increasing use of cinacalcet therapy (with accompanying reductions in serum Ca levels), the increasing use of vitamin D and its analogs (which increase Ca), and the increasing use of Ca-containing phosphate binders. The present study was conducted to examine the factors influencing transperitoneal calcium balance during continuous cycling peritoneal dialysis (CCPD) therapy, with particular attention to net ultrafiltration (UF) and serum ionized Ca (iCa).

Patients and Methods

This open, prospective cohort study included 40 medically stable patients maintained on CCPD for at least 3 months. Most patients used low-Ca (2.5 mEq/L) PD fluid; the Ca content of PD fluid for patients on icodextrin-based solutions was 3.5 mEq/L. Patients were instructed to record the quantity of dialysate instilled in a 24-hour period and net UF, and to bring a well-mixed aliquot of PD drainage to the dialysis unit. Concentrations of iCa and dialysate Ca were measured. Total Ca instilled into and drained from the PD fluid was calculated, and then the transperitoneal calcium balance was determined.

Results

Significant correlations were noted between transperitoneal calcium balance and both serum iCa ( r = –0.360) and the UF rate ( r = –0.708). Of the patients whose iCa was over 5 mg/dL, 71% were in negative calcium balance; of those with iCa levels below 5 mg/dL, 62% were in positive calcium balance. Of patients with UF below 1000 mL daily, 58% were in positive calcium balance; of those with 1000 mL UF or more, net Ca gain was noted in only 38%.

Conclusions

The present study demonstrates the importance of UF and iCa in determining transperitoneal Ca transport. These findings are of particular importance given the widening use of calcimimetic agents, vitamin D analogs, and Ca-based phosphate binders (all of which alter iCa) and the potential association between UF rate and outcome in PD patients.