Inhaled Versus Intravenous Milrinone for Patients Undergoing Mitral Valve Replacement Surgery

This prospective double blinded randomized study aims to compare the effect of inhaled versus intravenous milrinone on the pulmonary vascular resistance in patients undergoing mitral valve replacement surgery. The primary outcome is to determine change in pulmonary artery pressure. The secondary outcomes include, * Incidence of systemic hypotension. * Hemodynamic affection and need of vasopressors and inotropes. * Change in pulmonary vascular resistance versus systemic vascular resistance. * Right ventricular function. * Duration of mechanical ventilation. * Need for mechanical circulatory support devices. * Urine output * Length of intensive care (ICU) in stay. As the investigators hypothesize that inhaled milrinone has a selective pulmonary vasodilator effect devoid of the systemic hypotension with the intravenous administration.