Factors influencing transperitoneal calcium balance during CAPD

A dialysate containing a calcium concentration of 1.75 mmol/L has been the standard in CAPD for a long time. This concentration was chosen to achieve a positive calcium balance to suppress hyperparathyroidism. In the measurement of peritoneal calcium mass transfer, conflicting results have been published, with positive and negative calcium balances reported. These differences have been explained by differences in the filtration rate, and a negative correlation between the filtration rate and the peritoneal calcium mass transfer can be found. Whereas nearly all patients in this study had a negative calcium balance using a glucose solution of 3.86%, a wide variation was found for the 1.36% glucose solution. There were several patients who had a positive calcium balance despite a positive filtration rate. The explanation for this finding lay in differences in serum concentrations of calcium, and especially differences in the size of the total exchangeable calcium pool that contains the plasma calcium compartment. A negative correlation between peritoneal calcium balance and the size of the total exchangeable calcium pool could be demonstrated. This finding may explain the differences in the peritoneal calcium flux reported in the literature. As an enlargement of the exchangeable calcium pool correlates with the progression of vascular calcification, therapeutic efforts should be directed toward prevention of an enlargement of this pool.