Modulating the pulmonary circulation: an update

Pulmonary hypertension is a common finding in pulmonary circulatory disorders of different origin. Chronic pulmonary hypertension may develop due to either cardiopulmonary or systemic diseases whereas acute and acute-on-chronic pulmonary hypertension often occur in the course of cardiothoracic surgery. Right heart failure is the major risk particularly in the course of acute pulmonary hypertension. Thus, besides basic treatment of the underlying disease the use of vasodilators is a valuable therapeutic option to decrease right ventricular afterload, but intravenous vasodilators may provoke systemic arterial hypotension and impair gas exchange due to vasodilation of pulmonary shunt areas. Therefore, inhaled vasodilators such as nitric oxide and prostacyclin have been suggested for the treatment of pulmonary hypertension especially when concomitant hypoxemia is present due to a ventilation-perfusion mismatch. However, randomised controlled trials performed to evaluate long-term effects revealed different results: thus, in chronic pulmonary hypertension inhaled vasodilators improved outcome whereas the results for the treatment of the acute respiratory distress syndrome revealed beneficial effects only when used as a rescue and/or bridging therapy in severe hypoxemia. In cardiothoracic surgery, inhaled vasodilators have been shown to improve pulmonary circulation when severe pulmonary hypertension is present. Although effective in experimental studies no clear recommendation can be made in view to the use of other vasodilators such as phosphodiesterase inhibitors or endothelin antagonists. Likewise, the combination of different vasodilators merit further investigations to prove efficacy in randomised controlled trials.