Normalization of Priming Solution Ionized Calcium Concentration Improves Hemodynamic Stability of Neonates Receiving Venovenous ECMO

Abstract

The authors' objectives in this investigation were: 1) to prospectively determine whether a normocalcemic priming solution would result in elimination of hypocalcemia after the initiation of extracorporeal membrane oxygenation (ECMO); 2) to investigate whether normocalcemia would result in improvements in the patient's hemodynamics during the initiation of ECMO; and 3) to further define the relationship between ionized calcium measurements and total calcium, serum total protein, serum albumin, and total magnesium. This was a prospective study done in our neonatal intensive care unit, and included nine neonatal patients placed on ECMO for cardiopulmonary support. The bypass circuit was primed in the standardized manner with 100 mg calcium chloride. Circuit ionized calcium measurements were performed, and additional calcium chloride was added to normalize the ionized calcium in the priming solution. Ionized calcium was measured from the circuit and the patient before the initiation of ECMO, and then again from the patient 5, 10, 15, 30, 60, 120, and 240 minutes after the initiation of ECMO. The patients' mean arterial pressure was measured simultaneously with each ionized calcium measurement. Ionized calcium, serum total calcium, total protein, serum albumin, and total magnesium were measured from blood samples simultaneously collected four times daily. There was no significant change in the ionized calcium measured in the patients after the initiation of ECMO. There was, however, a significant increase in blood pressure 5 min after the initiation of ECMO (62 +/- 7 mmHg vs 53 +/- 6 mmHg, p = 0.01). Thereafter, there was no difference in blood pressure measured when compared with pre ECMO values. A poor correlation was demonstrated between ionized calcium and total calcium (r2 = 0.35), serum total protein (r2 = 0.26), serum albumin (r2 = 0.27), and total magnesium (r2 = 0.05). On the basis of the authors' data, the initiation of ECMO with a normocalcemic prime results in a minimal change in patient ionized calcium and resolution of the hypotension previously observed. In addition, there was poor correction between ionized calcium, total calcium, and other indirect measures of ionized calcium. Ionized calcium measurements are critical for patient hemodynamic stability before bypass and should be normalized in both the patient and priming solution before the initiation of bypass.