Oxygenation index ( OI ) , difference of alveoli-arterial oxygen pressure ( P ( A - ) O2 ) , static lung compliance ( Cstat ) , and airway resistance ( Raw ) were measured before caridopulmonary bypass ( CPB , T1 ) , 20 minutes after the CPB ( T2 ) , 2 h after the operation ( T3 ) , 6 h after the operation ( T4 ) and 12 h after the operation ( T5 ) .