Intra-operative Fraction of Inspired Oxygen and Lung Injury in Coronary Artery Bypass Grafting Surgery

Inclusion Criteria: * Age from 18 to 75 * BMI from 20 to 39.9 * ASA II/III * Undergoing isolated selective on-pump CABG through median sternotomy * Subsequent admission to an intensive care unit (ICU). Exclusion Criteria: * with severe chronic obstructive pulmonary disease (COPD) * Pregnant woman. * With current acute coronary syndrome (\<1 week) * Severe anemia (hemoglobin \<10g/L) * Preoperative supplemental oxygen requirement to maintain arterial O2 of 92%, * Right to left shunt in heart * Carotid stenosis defined as \>50% stenosis of either carotid artery, * Cardiac surgery that requires intraoperative circulatory arrest, * Current use of dialysis, * One-lung ventilation during surgery, * Recent smoking (within 1 month), * Non-respiratory reason to reintubate or delayed extubation such as bleeding or heart failure, * Perioperative allogenic transfusion with red blood cell, plasma or platelet