Effect of high bicarbonate hemodialysis on ionized calcium and risk of metastatic calcification.
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.
Kirschbaum
Barry
B
Division of Nephrology, Department of Internal Medicine, Virginia Commonwealth University, P.O. Box 980160, Richmond, VA 23298, USA. bkirschb@hsc.vcu.edu
D000328:Adult; D000368:Aged; D000471:Alkalosis / Q000097:blood / Q000139:chemically induced / Q000378:metabolism; D001639:Bicarbonates / Q000494:pharmacology*; D002114:Calcinosis / Q000097:blood / Q000139:chemically induced* / Q000378:metabolism; D002118:Calcium / Q000097:blood* / Q000737:chemistry / Q000378:metabolism*; D002245:Carbon Dioxide / Q000097:blood; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D008875:Middle Aged; D010710:Phosphates / Q000097:blood; D006435:Renal Dialysis / Q000009:adverse effects*; D012307:Risk Factors
D001639:Bicarbonates; D007477:Ions; D010710:Phosphates; D002245:Carbon Dioxide; D002118:Calcium