Universal calcium (Ca) therapy in the first days of life for VLBW infants with a total serum Ca < 7.0 mg/dl may pose unnecessary risks. Total serum Ca may not adequately reflect Ca status. We evaluated the use of ionized Ca obtained with blood gas measurements in a clinical setting to determine if we could decrease the number of infants treated for hypocalcemia. Forty infants< 1500 grams birthweight requiring mechanical ventilation were enrolled in the study. Both ionized Ca and total serum Ca were simultaneously measured at 12, 24, 36, and 48 hours of age. A Smooth E syringe from Radiometer was used to collect 0.3 ml of blood for an ABG and ionized Ca and values measured on a Radiometer ABL 505 Analyzer. The total serum Ca was measured on a Kodax EKTACHEM 700 Chemistry Analyzer. An EKG was obtained at 24 hours of life to evaluate changes associated with hypocalcemia. Infants were also assessed for any clinical symptoms of hypocalcemia. If the ionized Ca was < 0.80 mmol/l, therapy for hypocalcemia was instituted.

We found 28/40 infants had total serum Ca values less than 7.0 mg/dl. Of these 28, only 7 had an ionized Ca < 0.8 mmol/l. Using this approach, no infant had clinical or EKG evidence of hypocalcemia. A total of 10/40 infants had a serum Ca less than 5.5 mg/dl. Of these 10 infants, 6 had an ionized Ca< 0.8 mmol/l which indicates that some infants may maintain a normal ionized Ca despite a very low total Ca.

Of 133 measurements of ionized Ca in the 40 infants, 10 were < 0.80 mmol/l. Of these 10 low ionized Ca measurements, 8 were associated with a pH> 7.40 and 5 of the 8 were associated with a pH > 7.50. These results demonstrate a close link between alkalosis and ionized hypocalcemia in VLBW infants.

Conclusion: In non-alkalotic VLBW infants, Ca therapy is generally not needed in the first 2 days of life. Ca status of these infants may be monitored safely by using ionized Ca.