One-lung ventilation during thoracic surgery may affect systemic oxygenation and peripheral microcirculation by hypoxic pulmonary vasoconstriction. Both intravenous and inhalational anesthetics can be used during one-lung ventilation. However, there is still a controversy which anesthetic would be more appropriate during one-lung ventilation in the perspective of oxygenation and microcirculation. The investigators hypothesized that intravenous and inhalational anesthetics may affect oxygenation and microcirculation differently during one-lung ventilation.

Patients undergoing thoracic surgery including one-lung ventilation will be randomized to receive intravenous (propofol) or inhalational (desflurane) anesthetic.

Systemic oxygenation can be evaluated by measuring partial pressure of oxygen in arterial blood analysis. Microcirculatory parameters can be obtained from vascular occlusion test. Among those parameters, recovery slope during vascular occlusion test is known to reflect recruitment of microvasculature in response to hypoxic or ischemic insult. In this study, we will compare arterial partial pressure of oxygen and recovery slope during one-lung ventilation between propofol and desflurane group.

Inclusion Criteria:

• undergoing thoracic surgery including one-lung ventilation

Exclusion Criteria:

• refuse to enroll
• BMI over 30 kg/m(2)
• severe obstructive or restrictive lung disease
• preoperative supplemental oxygen, intubated, or mechanical ventilatory support
• preoperative arterial partial pressure of oxygen < 60 mmHg
• pregnancy
• history of coronary artery disease
• preoperative continuous infusion of vasopressor or inotropes
• cannot undergo vascular occlusion test: anatomical abnormality of both arms, severe peripheral vascular disease, presence of A-V fistula