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.