Calcium ion activity in the sick neonate: effect of bicarbonate administration and exchange transfusion.

Abstract

Extract: Calcium ion activity was measured in plasma obtained by venous or arterial puncture using a calcium-selective flow-through electrode. Mean level of ionized calcium in umbilical venous plasma was 2.48 ± 0.04 mEq/liter. Within 30 hr after birth, the values decreased in sick infants to 1.35 ± 0.11 mEq/liter. Total calcium concentra tions were in the normal adult range at birth (5.20 ± 0.08 mEq/liter), showing a subsequent decline to subnormal values (3.47 ± 0.28 mEq/liter at age 30–40 hr). A calcium ion activity of less than 1.4 mEq/liter was associated with total calcium level at or below 3 mEq/liter in 80% of patients. Symptoms and signs attributable to hypocalcemia (ionized fraction) or hypomagnesemia, or both, were found only in infants in whom plasma levels of both divalent cations were below the lower limit of normal. Administration of NaHGO3 for acidosis caused a slight rise in pH (from 7.20 to 7.28 mEq/liter) and a decrease in plasma calcium ion activity (from 1.68 to 1.51 mEq/liter). During exchange transfusion with acid-citrate-dextrosc (ACD)-Tham buffered blood, calcium ion activity decreased significantly from 1.90 ± 0.08 to 1.20 ± 0.09 mEq/liter, whereas total calcium levels increased consistently (from 4.22 ± 0.13 to 5.33 ± 0.15 mEq/liter).Speculation: The temporary hypocalcemia, observed in sick newborn infants, may also occur in healthy newborns. It is thought to initiate normal calcium homeostasis by stimulating parathormone secretion and by bringing into play the two feedback mechanisms for calcitonin and parathormone secretion.