The Relation of Post-Dialysis Plasma Calcium and Magnesium to the Dialysate Levels and to Changes in Blood pH

Abstract

The mechanism of the rise in plasma calcium and magnesium reported after hemodialysis was investigated by in vitro equilibrium dialysis using a combined membrane lung and kidney. Correction of 0.1 pH unit by dialysis resulted in an average rise of 0.8 mg in total plasma calcium, owing to the increase in the protein-bound fraction, whereas the decrease in the pH to below normal had the opposite effect. The fall in Pco₂ with a rising blood pH during dialysis seemed to exert the major influence in increasing the protein-bound calcium and magnesium. The relation between dialysate and post-dialysis plasma calcium and magnesium at the normal pH may be expressed by the ratios 1:1.70 and 1:1.46 respectively. The rise in plasma calcium and magnesium after dialysis is caused by the correction of blood pH during hemodialysis or by the use of high concentrations of these ions in the dialysate.