Hemodynamic effects of amrinone in children after cardiac surgery

Abstract: The hemodynamic effects of amrinone were assessed in seven children following cardiac surgery. Amrinone was administered as a bolus of 1 mg kg⁻¹ body wt., followed by continuous infusion at 10μg kg⁻¹ min⁻¹ for 1h and two stepwise increases to 20 and 40μg kg⁻¹ min⁻¹ for 30 min each. Hemodynamic data were obtained and plasma concentrations of amrinone measured 1 h after the bolus dose and immediately before each increment of the infusion rate. Amrinone levels ranged from 0.7 to 2.3 mgl⁻¹. Administration of amrinone lowered systemic vascular resistance from 20.04.3 to 16.54.6 mmHgl⁻¹ min⁻¹ m⁻² (p<0.05) and reduced mean arterial pressure from 71.79.5 to 62.613.5 mmHg (p<0.05) at the highest infusion rate, confirming the known vasodilative effect of the drug. However, these effects did not result in a statistically significant increase in stroke volume (35.07.5 to 35.57.0ml m⁻², NS) or cardiac index (3.100.50 to 3.200.40 l min⁻¹ m⁻²). One additional patient, in whom a higher loading dose was tried in order to achieve a higher plasma concentration, developed systemic hypotension. A correlation was established between the plasma concentrations of amrinone and the percentage decrease in systemic resistance (r=0.70,p<0.05). These results suggest that in children after open heart surgery, amrinone acts primarily as a systemic vasodilator, with questionable inotropic effect. Accordingly, its use should be restricted to children with severe cardiac failure and documented highly elevated afterload.