Postoperative delirium (POD) is an acute brain dysfunction characterized by inattention, impaired consciousness, and cognitive and orientation disturbances, and is a common complication after cardiac surgery. The high incidence of up to 52% of POD in cardiac surgery patients lead to a range of adverse clinical outcomes.The brain tissue is enclosed in a rigid anatomical structure; when there is an obstruction to venous return from the brain, intracranial pressure can increase, and blood supply to the brain tissue can decrease, leading to central nervous system dysfunction.

Systemic venous congestion can occur when there is right heart dysfunction or excessive volume load. When right heart failure and/or volume overload occurs, changes in right atrial pressure are transmitted to the venous system of organs throughout the body, with dilatation of the inferior vena cava (IVC), obstruction of blood return from the hepatic, portal, and renal veins, and abnormal venous flow signals and altered ultrasound Doppler flow patterns.

The primary objective of this prospective cohort study is to explore if intraoperative systemic venous congestion is associated with POD after cardiac surgery. This study will also investigate the relationship between intraoperative systemic venous congestion and postoperative complications, and the relationship between each separate venous congestion and POD after cardiac surgery.

Inclusion Criteria:

1. Patients scheduled to undergo elective cardiac surgery via a midline thoracic incision;
2. ≥18 years;
3. A preoperative MMSE score>23, without consciousness or language barriers, capable of cooperating with neurological examinations, cognitive function tests, and other assessments of neurological function.

Exclusion Criteria:

1. Contraindications for TEE;
2. Emergency cardiac surgery;
3. Major vascular surgery;
4. Redo cardiac surgery;
5. Severe infection requiring continuous antibiotic therapy;
6. Severe preoperative heart failure with left ventricular ejection fraction < 30%;
7. A critical preoperative state (mechanical circulatory support, extracorporeal membrane oxygenation, current renal replacement therapy, mechanical ventilation, or cardiac arrest necessitating resuscitation);
8. Multi-organ dysfunction;
9. Known conditions that may interfere with the assessment or interpretation of hepatic vein, portal vein blood flow (such as liver cirrhosis or portal vein thrombosis) or the renal vein blood flow (such as urinary tract obstruction);
10. Planned cardiac transplantation or ventricular assist device implantation;
11. Pregnancy;
12. Insufficient ultrasonographic imaging;
13. Restarting CPB after first CPB cessation during surgery;
14. Requirement for cardiac assist devices (ECMO, IABP, or ventricular assist device) after CPB intraoperatively;
15. Neurological or psychiatric diagnoses that may affect cognitive performance or cognitive testing;
16. Documented delirium before surgery.

Patients scheduled to undergo elective cardiac surgery