Inhaled Pulmonary Vasodilators in Cardiac Surgery Patients: Correct Answer Is “NO”
Pulmonary hypertension often complicates the care of patients who are undergoing cardiac surgery. Severe acute pulmonary hypertension may contribute to the development or worsening of right ventricular (RV) failure. Pulmonary hypertension and RV failure may reduce left ventricular (LV) filling, LV systolic and diastolic pressures, and cardiac output and lead to systemic hypotension. Decreased arterial blood pressure may compromise LV and RV coronary perfusion at a time when RV end-diastolic pressures and RV myocardial oxygen consumption are increased due to increased RV wall tension, thereby leading to RV ischemia.1 RV ischemia exacerbates RV failure, causing a further reduction in cardiac output and blood pressure. Concomitant LV dysfunction further impairs RV performance due to the loss of the interventricular septal contributions to RV function, which are largely determined by LV function. One of the key interventions to break this vicious cycle is to reduce the RV afterload, for example, by decreasing pulmonary vascular resistance (PVR), thereby enabling the RV to pump more blood forward. Although systemic vasodilators may reduce PVR, concomitant reduction of systemic blood pressure not only decreases the RV coronary perfusion pressure but also decreases LV contraction, which adversely affects RV function. Inhalation of nitric oxide (NO) produces selective pulmonary vasodilation without reducing the systemic arterial pressure in patients with pulmonary hypertension.2 Although the only current Food and Drug Administration-approved indication of inhaled NO is persistent pulmonary hypertension of newborns, off-label use of inhaled NO is widespread. However, inhaled NO is very expensive; a number of other, potentially less expensive, experimental inhaled pulmonary vasodilators have been described, which may provide alternatives to inhaled NO. Despite the need to treat RV dysfunction in patients undergoing cardiac surgery, as well as patients undergoing heart and lung transplantation or requiring the placement of a ventricular assist device, there is no established consensus concerning the use of pulmonary vasodilators for these indications.