Blending low doses of NO gas with oxygen in the inspiratory limb of mechanical ventilators is an effective method for reducing pulmonary vascular resistance and decreasing extrapulmonary right-to-left shunting at the ductus arteriosus and foramen ovale in many patients with PPHN. However, in some patients with PPHN, sustained elevations of PVR may occur in the absence of or despite improvement in the parenchymal lung disease such that mechanical ventilation is not needed for maintaining adequate gas exchange.