Pharmacologic support of circulation in patients undergoing cardiac surgery

Maintenance of adequate oxygen balance to all tissues is one of the primary objectives when dealing with patients undergoing cardiac surgery. Cardiac output is one of the major components of oxygen delivery so that its maintenance is an important consideration. Due to pre-operative cardiac lesion and myocardial dysfunction secondary to the events related to cardiac surgery and cardiopulmonary by-pass, circulatory support by pharmacological or mechanical means is frequently required after surgery. Therefore, inotropes and vasodilators are used to improve the myocardial performance after cardiac surgery. Epinephrine, dopamine and dobutamine are commonly used inotropes. Dopexamine and phosphodiesterase inhibitors such as amrinone, milrinone and enoximone are some of the newer agents that have been introduced in clinical practice. Amongst the vasodilators, sodium nitroprusside and nitroglycerin are commonly used. Alpha adrenergic blockers such as phentolamine and phenoxybenzamine and calcium channel blockers such as diltiazem are some other vasodilators that can be used. Many units still regard epinephrine as an inotrope of choice and use its predominant beta agonist effect in the dose range of 0.02 to 0.04 mg/kg/minute. Some prefer dobutamine and others a combination of inotrope and vasodilator or an inodilator. Phosphodiesterase inhibitors can be useful in certain situations such as pre-existing ventricular dysfunction or when stunning of the myocardium is suspected with down regulation of beta receptors. Dopamine is useful in the renal vasodilating dose to improve renal perfusion and improve output. There is no ideal inotrope at present and each one has its own drawbacks. The clinician must learn to use the inotropes (especially the newer ones) based on his own clinical experience.