Milrinone Versus Epinephrine for Right Ventricular Dysfunction After Cardiac Surgery in Adults: A Randomized Double-Blinded Trial

Epinephrine is the most potent adrenergic agonist which has positive inotropic and chronotropic effects and enhanced conduction in the heart (β1), smooth muscle relaxation in the vasculature and bronchial tree (β2), and vasoconstriction (α1). Low doses of this agent (<0.1-0.2 μg/kg/min) mainly activate the β adrenoceptors with inotropic effects. Higher doses result in vasoconstrictor effect which takes the lead. Other effects include bronchial dilation, mydriasis, glycogenolysis, tachyarrhythmia, myocardial ischemia, pulmonary hypertension, hyperglycemia, and lactic acidosis. Epinephrine also reduces splanchnic and hepatic perfusion and increases metabolic workload of the liver. So this hypermetabolism that impairs oxygen exchange, glycolysis, and suppression of insulin cause lactic acidosis.

Milrinone is a phosphodiesterase-III inhibitor. This effect decreases the degradation of cyclic adenosine monophosphate (cAMP), increases the cAMP levels in cells, and then increases activation of protein kinase A. Therefore, its cardiac effects are positive inotropy and improved diastolic relaxation. Milrinone also causes potent vasodilation, with reduction in preload, afterload and pulmonary vascular resistance. Considering its characteristics, milrinone might be a useful agent for cardiac surgery patients.