Old and new inotropic drugs

The rational selection of inotropic drugs in cardiac surgery

Despite improvements in surgical technique and intraoperative myocardial protection, certain patients have need for inotropic drug support after cardiac surgery. This review examines drugs that are currently in use for inotropic support of the heart, including calcium, epinephrine, dopamine, dobutamine, isoproterenol, and amrinone. Patient factors that may have an impact on the selection of appropriate drugs are also examined. Application of these data to specific patients must be guided by the particular hemodynamic derangements present. Careful analysis of the specific hemodynamic disorder and tailoring of inotropic therapy to these abnormalities are crucial. Such a rational approach to the selection of inotropic agents requires continuous hemodynamic assessment and recognition that the patient's condition and needs may change rapidly early after heart surgery dictating adjustment of subsequent therapy.

The use of low doses of dopamine in intensive care medicine

The dopamine alpha- and beta-adrenoceptor dose-response curves are investigated in four patients who are exempt from cardiovascular disease. A dose-related increase in CO, HR and SV is observed with infusion rates of up to 3 micrograms kg-1 min-1. With concentrations greater than 10 micrograms kg-1 min-1, both BP and SVR increase. Low-dose dopamine infusion less than 3 micrograms kg-1 min-1 is investigated in ten other patients. With this infusion rate, a selective renal vasodilation is induced without peripheral or cardiac beta-adrenoceptor activation. Dopamine is responsible for an increase in diuresis FENa, GFR and RBF. These properties are indicated in renal failure, and when haemodynamic support is required in cardiac failure, if an infusion rate of up to 10 micrograms kg-1 min-1 is able to reverse cardiac insufficiency.

The new inotropic phosphodiesterase inhibitors

Compounds with phosphodiesterase inhibitory activity stimulate myocardial contractility by increasing the intracellular cyclic AMP concentrations. They can also increase Ca2+ entry and inhibit Ca2+ sequestration by the sarcoplasmic reticulum. Xanthines produce bronchodilation with associated venous and arteriolar dilation. However, their use is limited by their positive chronotropic effect and other side effects at high plasma levels. New phosphodiesterase inhibitors have been perfected: they are more specific with little chronotropic effect. Increasing the sensitivity of the myofilaments to Ca2+, and other unclear mechanisms may be involved in the inotropic action of these drugs. These new promising active compounds are described and discussed. They augment cardiac performance and improve regional distribution of blood flow and symptoms. However, their influence on the long-term outcome of severe heart failure has yet to be determined.