The case is described of a 29-year-old man with
renal failure and recurrent
hyperparathyroidism who 3 weeks postparathyroidectomy developed hypocalcemic
tetany because he was taking one-half the prescribed dose of
calcitriol. He interpreted his symptoms as those of
potassium intoxication and self-administered almost 1,500 mEq
sodium bicarbonate. The increase in plasma
sodium and osmolarity led to increased fluid intake, and at presentation he had an ionized
calcium of 0.50 mmol/L, K 5.3 mmol/L, Na 148 mmol/L, total CO2 52.6 mmol/L, pO2 51.2 mm Hg, and pH of 7.61. He had gained 7 kg in weight. All abnormalities were corrected by dialysis, using initially a
calcium-free
dialyzate with extra
calcium infused. The case illustrates the effect of
alkalosis in reducing the amount of
calcium that exists in ionized form, and it is suggested that complexing of
calcium as
calcium bicarbonate together with the pH change contributed to the decrease in ionized
calcium. It is also an example of the hazards of treating patients who devise their own therapeutic regimens.