The purpose of this study is to investigate effect of increasing inspiratory time (I:E ratio 1:1) on intrapulmonary shunt fraction and oxygenation during one lung ventilation in the lateral decubitus position.

Increasing inspiratory time(e.g. Inverse ratio ventilation) has been known that had advantage of alveolar recruitment, preventing of ateletasis. On the contrary, it has disadvantange of intrinsic PEEP, air trapping. There is few study on one lung ventilation in lateral decubitus position about this ventilation method. We were going to investigate effecf of this ventilation method.

Inclusion Criteria:

• ASA physical status class I, II
• Use of Double lumen tube
• Unilateral lung lobectomy

Exclusion Criteria:

• COPD
• CAOD
• Unstable hemodynamic status
• Peak airway pressure > 30mmHg (Two lung ventilation)