Inclusion Criteria:  All patients at ages between 22 to 80 years old, American Society of Anesthesiologists Physical Status (ASA-PS) risk groups of 1 to 3 Elective thoracic surgery Operational types of thoracic surgery include; either open lung resection with thoracotomy or video-assisted thoracic surgery (VATS) operative procedure along with general a anesthesia, DLT insertion, and OLV for all patients  Exclusion Criteria:  Refusal to participate in a study, History of severe asthma, Severe renal and hepatic insufficiencies, Pregnancy, History of previous pulmonary resection, Hemoglobinopathies.