Use of inotropic and chronotropic agents in neonates.

The determinants of cardiovascular function include preload, myocardial contractility, and afterload. Myocardial contractility and afterload can be altered pharmacologically and form the basis for the clinical management of shock with inotropic and chronotropic drugs. There are extensive data from experiments in laboratory animals that the immature cardiovascular system may respond differently to these inotropic and chronotropic agents than the mature cardiovascular system. Digitalis, isoproterenol, dopamine, and dobutamine are the most frequently used positive inotropic drugs in children. Because of maturational differences in pharmacokinetics, neonates require a larger weight-based dose of digoxin to achieve a similar serum level to adults, but neonates do not require a greater serum level of digitalis to achieve an equivalent inotropic effect as in adults. Isoproterenol increases heart and cardiac output but has no independent effect on renal blood flow. Dopamine is unique among sympathomimetic means because of its independent effect to increase renal and mesenteric blood flow. Dobutamine increases cardiac output with less chronotropic effect than isoproterenol but, unlike dopamine, does not have an independent effect on renal and mesenteric profusion. The "best" drug for a specific clinical situation depends on the complex interrelationship of the determinants of cardiovascular function and the underlying disease process. One drug may be more efficacious in a specific clinical setting than another drug. If the desired clinical response is not achieved with an adequate dose of one drug, a different drug or a combination of inotropic agents should be tried.