Arterial oxygen pressure ( PaO2 ) , arterial carbondioxide tension ( PaCO2 ) , O2 saturation ( SPO2 ) , mean arterial pressure ( MAP ) , heart rate ( HR ) , anesthetic effect , time of spontaneous breathing recovery , and time of resuscitation were recorded before operation ( T0 ) , immediately after skin incision ( T1 ) , immediately after sternotomy ( T2 ) , before suspension of cardiopulmonary bypass ( CPB , T3 ) , immediately after cardiac re-beating ( T4 ) , immediately after CPB cessation ( T5 ) , and at the end of surgery ( T6 ) .