Adequate Additional Bronchial Cuff Volume to Achieve Blood-tight Seal After Air-tight Seal in Double Lumen Tube

The purpose of this study is to find the adequate additional bronchial cuff volume after achievement of air-tight seal, that can achieve blood-tight seal(preventing leakage of blood through cuff) in double lumen tube

Inclusion Criteria:

• patients undergoing thoracic surgery under left lower decubitus position, using left sided double lumen tube
• patient's left main bronchus size adequate for 35Fr, 37 Fr, 39 Fr double lumen tube

Exclusion Criteria:

• dislocation or great movement of double lumen tube depth