The purpose of this study is to investigate a performance of initial positioning of left sided double lumen endobronchial tubes using peak inspiratory pressures difference between two lungs.

If both lungs have relatively equal volumes and the double lumen tube is in a satisfactory position, peak inspiratory pressure between two lungs is similar or equal when each lumen is sequentially clamped while ventilating each lung with the same tidal volume. We are going to investigate a performance of this method by fiberoptic bronchoscopy view and depth of double lumen tube, and compare with an conventional auscultation method.

Inclusion Criteria:

• ASA physical status class I, II
• Use of double lumen tube
• Normal preoperative pulmonary function study

Exclusion Criteria:

• COPD
• Restrictive lung disease
• CAOD
• Unstable hemodynamic status
• Peak inspiratory pressure > 30 mm Hg (Two lung ventilation)