MILRINONE - SYSTEMIC AND PULMONARY HEMODYNAMIC-EFFECTS IN NEONATES AFTER CARDIAC-SURGERY

Objective: To evaluate the hemodynamic effects of intravenous milrinon e in neonates with low cardiac output after cardiac surgery. Design: P rospective cohort study. Setting: Pediatric cardiac intensive care uni t. Patients: Ten neonates with low cardiac output (cardiac index of le ss than or equal to 3.0 L/min/m(2)) after corrective cardiac surgery w ere 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 = 6, includ ing two with ventricular septal defect), tetralogy of Fallot (n = 2), truncus arteriosus (n = 1), and total anomalous pulmonary venous conne ction (n = 1). Interventions: Milrinone was intravenously administered in three stages: a) baseline stage, in which patients had a stable he modynamic status, ventilation and gas exchange, hemostasis, and body t emperature; b) loading stage, in which a 50 mu g/kg intravenous loadin g dose of milrinone was administered over 15 mins; and c) infusion sta ge, in which milrinone was continuously infused at 0.50 mu g/kg/min fo r 30 mins. Measurements and Main Results: The mean heart rate increase d after the loading stage (149 +/- 13 to 163 +/- 12 beats/min, p < .01 ) but slowed during the infusion stage (154 +/- 11 beats/min, p < .01 vs. loading stage). Both right and left atrial pressures were lowered in all ten neonates. Compared with baseline, mean arterial pressure de creased after the loading stage (66 +/- 12 to 57 +/- 10 mm Hg, p < .01 ) but did not decrease further at the infusion stage (59 +/- 12 mm Hg) ; changes in mean pulmonary arterial pressure were comparable. Cardiac index increased from a baseline mean of 2.1 +/- 0.5 to 3.0 +/- 0.8 L/ min/m(2) (p < .01) with the loading stage, and was maintained at 3.1 /- 0.6 L/min/m(2) during the infusion stage. Systemic vascular resista nce index decreased below baseline values with loading, from 2136 +/- 432 to 1336 +/- 400 dyne . sec/cm(5) . m(2) (p < .01), and pulmonary v ascular resistance index also decreased with loading dose of milrinone , from 488 +/- 160 to 360 +/- 120 dyne . sec/cm(5) . m(2) (p < .01). T here 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 arter ial pressures, and systemic and pulmonary vascular resistances, while improving cardiac index. Milrinone increases heart rate without alteri ng myocardial oxygen consumption. While milrinone appears to be effect ive and safe during short-term use, the relative distribution of inotr opic and vasodilatory properties of milrinone remains to be elucidated .