Effect of bicarbonate on neonatal serum ionized magnesium in vitro.

Sodium bicarbonate is used to treat metabolic acidosis, or to induce metabolic alkalosis in sick neonates. The aim of this study was to quantify the decrease in serum concentration of ionized magnesium ([Mg2+]) when sodium bicarbonate is added to neonatal serum in vitro. Sodium bicarbonate was added to 30 cord serum samples of term infants to reach incremental concentrations of 0 to 2.0 mEq/L and [Mg2+] was measured. Serum [Mg2+] decreased significantly with the addition of sodium bicarbonate. At incremental sodium bicarbonate concentrations of 1.0 to 2.0 mEq/L, which is within the range of the desired aim in the treatment of metabolic acidosis, the magnitude of the decrease in serum [Mg2+] was approximately 0.084 to 0.158 mmol/L (18% to 34%) from the average baseline value. The addition of sodium bicarbonate causes a significant decrease in [Mg2+]. From this in vitro study we speculate that fast infusion of sodium bicarbonate in human neonates may potentially cause a clinically significant decrease in serum [Mg2+].