Effects of low doses of inhaled nitric oxide combined with oxygen for the evaluation of pulmonary vascular reactivity in patients with pulmonary hypertension.

The purpose of this study was to evaluate the hemodynamic effects of inhaled nitric oxide in oxygen (NO + O2) in patients with pulmonary hypertension. Eighteen patients (median age 31.5 months) with pulmonary hypertension inhaled through a mask 100% O2 and 20 parts per million NO + inspired O2 fraction (FiO2) at 0.4. Hemodynamic measurements were made at baseline and after O2 and NO + O2 administration. The pulmonary vascular resistance index decreased after inhalation of O2 and NO + O2 (p = 0.0018 and p = 0.0003, respectively), the decrease being significantly greater after NO + O2 (p = 0.0311). Concerning the transpulmonary pressure gradient, a reduction occurred in values after O2 and NO + O2 inhalation when compared with baseline values (p = 0.0014 and p = 0.0008). In patients with congenital heart disease, an increase occurred in pulmonary blood flow after O2 (p = 0.0089) and NO + O2 (p = 0.0019) compared with baseline values, and an increase also occurred in the pulmonary/systemic blood flow ratio after NO + O2 (p = 0.0017). The main side effect related to NO + O2 was pulmonary congestion in 3 patients. Low doses of NO combined with O2 demonstrated a selective pulmonary vasodilator response in patients with pulmonary hypertension. Despite its use for testing pulmonary reactivity, inhalation of NO + O2 should be carefully administered because of the potential risk of pulmonary congestion.