Calcium mass transfer and kinetics in CAPD using calcium-free solutions.

In 12 continuous ambulatory peritoneal dialysis (CAPD) patients we evaluated peritoneal calcium mass transfer (CaMT), serum and effluent dialysate ionized calcium (iCa) changes, and the variations of the dialysate-to-plasma (D/P) ratio for calcium throughout 6-hour dwell exchanges with zero calcium, 1.25 mmol/L calcium (1.25 Ca), and 1.75 mmol/L calcium (1.75 Ca) peritoneal solutions. The infused ionized and total calcium were, respectively, 1.28 +/- 0.04 and 1.77 +/- 0.04 mmol/L with 1.75 Ca and 0.89 +/- 0.03 and 1.28 +/- 0.04 mmol/L with 1.25 Ca solutions. During CaMT studies, the ultrafiltration rate was 250 mL on average, and serum iCa 1.24 mmol/L. Calcium was gained by the patients (+0.41 +/- 0.6 mmol/L) using standard solutions. CaMT was -0.67 +/- 0.4 mmol/L with 1.25 Ca and -2.4 +/- 0.4 mmol/L with zero Ca solutions. Throughout the exchanges the D/P ratio for iCa decreased from 0.97 +/- 0.03 at 0 minutes to an equilibrium value (at about 240 minutes) of 0.84 +/- 0.03 with 1.75 Ca solutions, while it increased from 0.75 +/- 0.04 to 0.83 +/- 0.05 with 1.25 Ca solutions. After a 6-hour exchange with zero Ca, the D/P ratio for iCa was 0.76 +/- 0.04, significantly lower than the D/P ratio for urea (0.97 +/- 0.02), creatinine (0.89 +/- 0.06), and bicarbonate (0.98 +/- 0.02). In conclusion, dialysate and serum iCa are in equilibrium at a D/P ratio of about 0.84. Thus calcium is gained by the patients using 1.75 Ca solutions, and it is lost (both by diffusion and ultrafiltration) using 1.25 Ca solutions.(ABSTRACT TRUNCATED AT 250 WORDS)