Barry Kirschbaum1. 1. Division of Nephrology, Department of Internal Medicine, Virginia Commonwealth University, P.O. Box 980160, Richmond, VA 23298, USA. bkirschb@hsc.vcu.edu
Abstract
BACKGROUND: Disturbances in calcium and phosphate metabolism among chronic hemodialysis patients result in renal osteodystrophy and vascular calcification. Even though it is the ionized fraction of calcium that is metabolically active, this measurement is generally not available and decisions are made on the basis of total calcium. Formulae to predict ionized calcium concentrations are available. METHODS: The OPTI Critical Care Analyzer with E-Ca cuvettes was used on-site to measure acid-base parameters, electrolytes, and ionized calcium. Additional assays included total calcium, phosphate, and albumin. RESULTS: Using a dialysate with 1.25 or 1.5 mmol/l calcium and 40 mmol/l bicarbonate, we observed a statistically significant increase in pH and total CO2 concentrations in post-dialysis blood. Total and ionized calcium increased significantly only in the patients with central venous catheters but not in those with fistulas or grafts. All patients experienced a decrease in phosphate concentrations. CONCLUSIONS: The metabolic alkalosis induced by high bicarbonate dialysate was not associated with a decrease in ionized calcium or a change in the calculated concentration product ratio for hydroxyapatite formation in the immediate post-dialysis period. However, if a 40% phosphate rebound were to occur 2 h after termination of dialysis, the calculated risk of metastatic calcification would increase 2.8-fold compared to pre-dialysis conditions. Formulae to calculate ionized calcium are not useful in this population.
BACKGROUND: Disturbances in calcium and phosphate metabolism among chronic hemodialysis patients result in renal osteodystrophy and vascular calcification. Even though it is the ionized fraction of calcium that is metabolically active, this measurement is generally not available and decisions are made on the basis of total calcium. Formulae to predict ionizedcalcium concentrations are available. METHODS: The OPTI Critical Care Analyzer with E-Ca cuvettes was used on-site to measure acid-base parameters, electrolytes, and ionizedcalcium. Additional assays included total calcium, phosphate, and albumin. RESULTS: Using a dialysate with 1.25 or 1.5 mmol/l calcium and 40 mmol/l bicarbonate, we observed a statistically significant increase in pH and total CO2 concentrations in post-dialysis blood. Total and ionizedcalcium increased significantly only in the patients with central venous catheters but not in those with fistulas or grafts. All patients experienced a decrease in phosphate concentrations. CONCLUSIONS: The metabolic alkalosis induced by high bicarbonate dialysate was not associated with a decrease in ionizedcalcium or a change in the calculated concentration product ratio for hydroxyapatite formation in the immediate post-dialysis period. However, if a 40% phosphate rebound were to occur 2 h after termination of dialysis, the calculated risk of metastatic calcification would increase 2.8-fold compared to pre-dialysis conditions. Formulae to calculate ionizedcalcium are not useful in this population.
Authors: Alan Peralta-Ramírez; Ana Isabel Raya; Carmen Pineda; Mariano Rodríguez; Escolástico Aguilera-Tejero; Ignacio López Journal: Nephron Extra Date: 2014-07-02