Mass transfer of calcium across the peritoneum at three different peritoneal dialysis fluid Ca2+ and glucose concentrations

2003 
Mass transfer of calcium across the peritoneum at three different peritoneal dialysis fluid Ca 2+ and glucose concentrations. Background In peritoneal dialysis, the rate of ultrafiltration has been predicted to be a major determinant of peritoneal calcium (Ca 2+ ) removal. Hence, dialysis fluid glucose concentration should be an important factor governing the transperitoneal Ca 2+ balance. The aim of this study was to test the effect of various dialysate glucose levels and selected dialysate Ca 2+ levels on Ca 2+ removal in peritoneal dialysis patients. Methods Patients ( N = 8) received, during a 7-week period, 2L of lactate (30mmol/L)/bicarbonate (10mmol/L)–buffered peritoneal dialysis solutions containing either 1.5% glucose and 1.0mmol/L Ca 2+ or 2.5% glucose and 1.6mmol/L Ca 2+ , or 4% glucose and 2.5mmol/L Ca 2+ , respectively, provided in a three-compartment bag (trio system). Patients underwent standardized (4-hour) dwells, one for each of the three dialysates to assess permeability-surface area product (PS) or mass transfer area coefficients (MTAC) for ionized and "freely diffusible" Ca 2+ , lactate, glucose, bicarbonate, phosphate, creatinine, and urea. Results There was a clear-cut dependence of peritoneal Ca 2+ removal on the rate of ultrafiltration. For large peritoneal to dialysate Ca 2+ gradients (2.5mmol/L Ca 2+ in 4% glucose) a close fit of measured to simulated data was predicted by the three-pore model using nonelectrolyte equations. For low transperitoneal Ca 2+ concentration gradients, however, directly measured Ca 2+ data agreed with the simulated ones only when the peritoneal Ca 2+ PS was set lower than predicted from pore theory (6mL/min). Conclusion There was a marked ultrafiltration dependence of transperitoneal Ca 2+ transport. Nonelectrolyte equations could be used to simulate peritoneal ion (Ca 2+ ) transport provided that the transperitoneal ion concentration gradients were large. Based on our data 1.38mmol/L Ca 2+ in the dialysis fluid would have created zero net Ca 2+ gain during a 4-hour dwell for 1.5% glucose, whereas 1.7 and 2.2mmol/L Ca 2+ would have been needed to produce zero Ca 2+ gain for 2.5% glucose and 3.9% glucose, respectively.
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