Study on the Relationship of Arterial-venous Oxygen Difference and Postoperative Complications After Cardiac Surgery.

The \>18 y/o patients who undergo cardiac surgery with cardiopulmonary bypass and with a preoperative additive EuroSCORE I≥ 6 are enrolled. Blood samples will be collected through arteries and central venous at the following intraoperative time points: before CPB, during CPB, and after CPB. The observation will end by hospital discharge or 28 days after surgery, whichever came first. The follow-up will continue for one year after surgery.