Inclusion Criteria:  • Age from 30 years to 70 years inclusive  elective cardiac surgery which included bypass, valve and ascending aortic surgery, a body mass index of > 35 kg/m2, postoperative treatment with mechanical ventilation, informed consent  Exclusion Criteria:  • GFI <30 ml/min before surgery, serum aspartate and alanine transaminase concentration greater than 80 U/l before surgery, left ventricular ejection fraction less than 30% before surgery.  Postoperative exclusion criteria:  chest tube drainage greater than 3 ml/kg/h, reoperation, myocardial infarction, need for high-dose inotropes or vasopressors or intraaortic balloon pump, presence of a bronchopleural fistula and refractory hypoxemia with an arterial oxygen tension to fractional inspired oxygen concentration ratio less than 150 mmHg, perioperative anaphylactic reaction, seizures, stroke, agitation