Milrinone hemodynamic effects

Dosing recommendations for milrinone include a loading dose of 50 mcg/kg, followed by an infusion beginning at 0.5 mcg/kg per minute (range 0.23 mcg/kg per minute for patients with renal failure up to 0.75 mcg/kg per minute). A loading dose is not necessary if immediate hemodynamic effects are not required or if patients have low systolic blood pressures (less than 90 mm Hg). Decreases in blood pressure during an infusion may necessitate dose reductions as well. 

Sodium nitroprusside is a mixed arterial-venous vasodilator that acts directly on vascular smooth muscle to increase cardiac index and decrease venous pressure. Despite its lack of direct inotropic activity, nitroprusside exerts hemodynamic effects that are qualitatively similar to those of dobutamine and milrinone. However, nitroprusside generally decreases PAOP, SVR, and blood pressure more than those agents do. 

In a randomized, open, parallel-group study of the hemodynamic effects of milrinone and glyceryl trinitrate in 119 patients with advanced decompensated heart failure, milrinone was significantly more effective than glyceryl trinitrate (7). Adverse effects caused the withdrawal of milrinone in three of the 58 patients who took it one had ventricular extra beats, one had renal insufficiency, and one had hypokalemia. Headache was the most common adverse effect in both groups, but was less common in those who took milrinone (12 versus 29%). 

A 74-year-old man had a tachycardia of 145/minute during infusion of milrinone after an operation for repair of an abdominal aortic aneurysm (15). The tachycardia was controlled by esmolol on one occasion and more impressively by metoprolol on a second occasion. However, the hemodynamic effects of mikinone were not altered by beta-blockade. 

Feneck RO, Sherry KM, Withington PS, Oduro-Dominah A European Milrinone Multicenter Trial Group. Comparison of the hemodynamic effects of milrinone with dobutamine in patients after cardiac surgery. J Cardiothorac Vase Anesth 2001 15(3) 306-15. 

In patients with elevated systemic vascular resistance and normal-to-elevated systemic blood pressure, afterload reduction with nitroprusside is logical it should be emphasized that nitroprus-side also increases venous capacitance, thereby also decreasing preload. In the context of myocardial dysfunction, afterload reduction will typically lead to improved forward cardiac output. Nitroprusside may also be effective when the systemic vascular resistance is elevated and systemic blood pressure is reduced the caveat in this more complex hemodynamic setting is that the load reduction produced by nitroprusside must be counterbalanced by an increase in stroke volume. This derivative increase in stroke volume may not occur in the patient with advanced heart failure rather, the result will be a further reduction in mean arterial pressure and the potential risk of peripheral organ hypoperfusion. An alternative approach would be the use of an inotropic-dilator drug such as milrinone, which will provide both preload and afterload reduction its concurrent positive inotropic effect may offset the reduction in mean arterial pressure that can occur from vasodilation alone. 

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