One-lung ventilation (OLV) is essential during mediastinal mass excision. However, OLV induces a drastic increase of intrapulmonary shunt due to maintained pulmonary perfusion through the nonventilated lung. In addition, it is reported that supine positioning of patient during OLV, which is required during mediastinal mass excision, results in worse oxygenation than lateral decubitus positioning.

Iloprost is a prostaglandin analogue and when inhaled during OLV, it acts selectively on the pulmonary vasculature, reducing pulmonary vascular resistance of well-ventilated lung and thereby alleviating ventilation-perfusion mismatch. The purpose of this study is to evaluate the effects of inhaled iloprost on oxygenation during one-lung ventilation in patients undergoing mediastinal mass excision.

Inclusion Criteria:

1. Patients scheduled for Video-assisted thoracoscopic surgery (VATS) mediastinal mass excision
2. Patient age from 20 to 80
3. American Society of Anaesthesiologists (ASA) physical status classification II~III

Exclusion Criteria:

1. Chronic obstructive pulmonary disease (COPD) with Forced expiratory volume in 1 second (FEV1) to Forced vital capacity (FVC) ratio < 0.7 and percentage of predicted FEV1 ≤ 80%
2. Diffusing capacity of carbon monoxide (DLCO) < 80%
3. Aspartate transaminase (AST) level ≥100 IU/mL or alanine transaminase (ALT) ≥ level 50 IU/L
4. Creatinine clearance ≤ 30mL/min
5. Congestive heart failure, arrhythmia
6. Unstable angina, coronary artery occlusive disease (CAOD), history of myocardial infarction within 6 months
7. Pulmonary edema, pulmonary arterial hypertension
8. Allergic to prostaglandin or prostacyclin analogue
9. Patients with peptic ulcer bleeding, trauma, intracranial hemorrhage
10. History of cerebrovascular disease (e.g. transient ischemic attack, stroke) within 3 months
11. Valvular heart disease
12. Pregnant women