Arterial partial pressure of oxygen ( PaO2 ) and fraction of inspired oxygen ( FIO2 ) were measured before anesthesia induction ( T0 ) , at skin incision ( T1 ) , after administration of heparin ( T2 ) , at 30 minutes after CPB weaning ( T3 ) , just before departure from the operating room to the intensive care unit ( ICU ) ( T4 ) , and 1 hour after ICU admission ( T5 ) , and PaO2/FIO2 ratio was calculated .