[Limitations of inhaled vasodilators]

Treatment of pulmonary hypertension is an important issue in intensive care. One therapeutic regimen involves the intravenous administration of prostacyclin (PGI2). This, however, is accompanied by diminished hypoxic pulmonary vasoconstriction, reduced arterial oxygenation, and systemic vasodilation. Thus, its clinical usefulness is limited. However, the inhalation of vasodilators such as nitric oxide (NO) or nebulized PGI2 causes a selective pulmonary vasodilation in ventilated alveoli and improved gas exchange, without any systemic vasodilation. It has therefore gained importance for the treatment of pulmonary failure associated with high shunt fractions. However, the inhalation of vasodilators may have adverse effects: in the case of NO, toxic side effects are predominant (MetHb, NOx), whereas in the case of PGI2, technical problems in terms of dosing and administration safety are of major interest. Furthermore, some patients do not respond to the treatment. In some individuals a reduction in pulmonary hypertension can be seen, while others lack even pulmonary vasodilation. The exact pathophysiological mechanisms remain to be investigated.