 Sixty patients undergoing lobectomy using one lung ventilation by double lumen tube will be included in this study. These patients will be divided into 2 groups. Groups S which will be included non smoking and secondary smoking and group SS which will be included secondary smoking smoking near him more than 10 cigarettes per day fore more than 5 years. Intra and postoperative arterial oxygen tension, arterial carbon dioxide tension and intraoperative peak airway pressure will be compared between the two groups. 