 Hypoxemia is a common complication after aortic surgery. As this complication has an adverse effect on the postoperative course of the patient, early treatment is important; however, the mechanism of hypoxemia after surgery for acute aortic dissection remains unclear. Recently, the investigators found that inhaled Nitric Oxide can improve the oxygenation in some of these patients. The investigators are trying to evaluate the effectiveness and safety of inhaled Nitric Oxide in patients with refractory hypoxemia after aortic surgery. 