<qa>  How many patients will be included in this study?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. 