Con: Amrinone is not a first-choice inotrope following cardiopulmonary bypass

Abstract

T HE QUESTION whether amrinone or any other inotropic drug is the first choice is an oversimplification of hemodynamic management. Such a question may have been acceptable two decades ago prior to routine cardiac output (CO) measurements and befcre the feasibility of rapidly calculating the various hemodynamic indices. Inotropic agents are mainly indicated for treatment of a low CO syndrome. Their main action, as their name implies, is enhancing myocardial contractility. The ideal inotropic agent, which does not affect other hemodynamic parameters and has no side effects, does not yet exist. The undesirable side effects of inotropic agents on heart rate (HR), systemic vascular resistance (SVR), and the myocardia1 oxygen supply/demand balance must be taken into consideration when selecting a drug. Impaired myocardial performance and a low CO can be due to various factors including, but not limited to, hypovolemia, metabolic abnormalities, decreased myocardial oxygenation, preoperative cardiac disease, and associated drug therapy. Impaired myocardial function may be more evident in either the right or left side of the heart, and the hemodynamic management of this situation differs from the management of global cardiac dysfunction. Low CO can be accompanied by several other hemodynamic variables, dysrhythmias, tachycardia, bradycardia, and increased or decreased SVR and PVR. For example, in cardiac surgery immediately following cardiopulmonary bypass (CPB), the decrease in blood pressure (BP) may be due to a low SVR in the presence of a CO higher than normal values. Such a decrease in SVR can be due to hemodilution and/or the initial effect of warming. In this situation, treatment of a low BP should be directed toward normalizing SVR with a vasopressor rather than the habitual use of an inotrope, which may increase MVO?.’ Myocardial dysfunction varies in its extent and different inotropic agents have different potenties. In acute situations, such as in cardiac surgery following CPB, a heart that was arrested for a long time and exposed to surgical manipulations frequently needs a very potent inotropic agent. Coronary patients are known to have low contractility indices and require larger doses of potent inotropic agents. In these patients, when a low CO is due to myocardial ischemia, the effect of the vasoactive drug on the balance between myocardial oxygen supply and demand becomes the most crucial factor in determining the choice of the