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.