Inhalation of nitric oxide has been reported to alter pulmonary blood flow in animal and human studies. This effect is related to the relaxant action of nitric oxide on arterial vascular smooth muscle cells. When nitric oxide is administered by inhalation, this effect is limited to the pulmonary vasculature as it is rapidly inactivated by hemoglobin as soon as it enters the blood stream. The effect of inhaled nitric oxide is more pronounced in well ventilated areas of the lung, where it promotes redistribution of pulmonary blood flow to regions with high ventilation-perfusion ratio decreasing pulmonary hypertension and improving oxygenation. Nitric oxide has been used to treat pulmonary hypertension and hypoxemia that occurred in thoracic surgery during one lung ventilation, postpneumonectomy pulmonary edema and lung transplantation. Inhaled nitric oxide may be a useful tool in patients with a low PaO2/FiO2 ratio during one lung ventilation. Further powered studies are still required to define the dose and timing of inhaled nitric oxide in patients who do have ischemia-reperfusion injury after lung transplantation.
