A Comparison of the Hemodynamic Effects of Amrinone and Sodium Nitroprusside in Infants After Cardiac Surgery

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Abstract
The phosphodiesterase inhibitor amrinone (AMR) in- creases cardiac output in children after cardiac surgery. In vitro, amrinone has both positive inotropic and vaso- dilatory effects. However the relative contribution of these effects to the increases in cardiac output observed clinically is unclear, and it has not been demonstrated that amrinone offers a hemodynamic advantage above that of pure vasodilators in infants. We compared the hemodynamic effects of AMR and sodium nitroprus- side (SNP) in 10 infants after cardiac surgery. Cardiac index (CI) was measured by thermodilution after SNP administration, titrated to decrease mean blood pres- sure (MBP) by 20%, and then after a 1.5-mg/kg bolus dose of AMR. Each patient served as his or her own control. Preload, as measured by left atria1 pressure and transesophageal echocardiography (in eight patients), was kept constant throughout the protocol. Both SNP and AMR caused significant decreases in MBP and sys- temic vascular resistance index (SVRI). However, only AMR resulted in a significant increase in CL The ratio of fractional increase in CI to fractional absolute decrease in MBP was significantly greater for AMR than SNP, indicating greater efficacy for AMR in the treatment of low cardiac output syndrome and suggesting that, in infants after cardiac surgery, AMR has clinically rele- vant positive inotropic effects.