Objective: To evaluate the hemodynamic effects of intravenous milrinone in neonates with low cardiac output after cardiac surgery.
Design: Prospective cohort study.
Setting: Pediatric cardiac intensive care unit.
Patients: Ten neonates with low cardiac output (cardiac index of less than equals 3.0 L/min/m2) after corrective cardiac surgery were enrolled in the study. The neonates' ages ranged from 3 to 27 days (median 5) and their weights ranged from 2.0 to 4.8 kg (median 3.7). The diagnoses were: transposition of the great arteries (n equals 6, including two with ventricular septal defect), tetralogy of Fallot (n equals 2), truncus arteriosus (n equals 1), and total anomalous pulmonary venous connection (n equals 1).
Interventions: Milrinone was intravenously administered in three stages: a) baseline stage, in which patients had a stable hemodynamic status, ventilation and gas exchange, hemostasis, and body temperature; b) loading stage, in which a 50 micro gram/kg intravenous loading dose of milrinone was administered over 15 mins; and c) infusion stage, in which milrinone was continuously infused at 0.50 micro gram/kg/min for 30 mins.
Measurements and Main Results: The mean heart rate increased after the loading stage (149 plus minus 13 to 163 plus minus 12 beats/min, p less than .01) but slowed during the infusion stage (154 plus minus 11 beats/min, p less than .01 vs. loading stage). Both right and left atrial pressures were lowered in all ten neonates. Compared with baseline, mean arterial pressure decreased after the loading stage (66 plus minus 12 to 57 plus minus 10 mm Hg, p less than .01) but did not decrease further at the infusion stage (59 plus minus 12 mm Hg); changes in mean pulmonary arterial pressure were comparable. Cardiac index increased from a baseline mean of 2.1 plus minus 0.5 to 3.0 plus minus 0.8 L/min/m2 (p less than .01) with the loading stage, and was maintained at 3.1 plus minus 0.6 L/min/m2 during the infusion stage. Systemic vascular resistance index decreased below baseline values with loading, from 2136 plus minus 432 to 1336 plus minus 400 dyne centered dot sec/cm5 centered dot m2 (p less than .01), and pulmonary vascular resistance index also decreased with loading dose of milrinone, from 488 plus minus 160 to 360 plus minus 120 dyne centered dot sec/cm5 centered dot m2 (p less than .01). There was no change in the rate pressure index, an indirect measurement of myocardial oxygen consumption, throughout the study.
Conclusions: Administration of milrinone in neonates with low cardiac output after cardiac surgery lowers filling pressures, systemic and pulmonary arterial pressures, and systemic and pulmonary vascular resistances, while improving cardiac index. Milrinone increases heart rate without altering myocardial oxygen consumption. While milrinone appears to be effective and safe during short-term use, the relative distribution of inotropic and vasodilatory properties of milrinone remains to be elucidated.
(Crit Care Med 1995; 23:1907-1914)