Postoperative delirium is an important problem in patients undergoing major cardiac surgery and associated with more complicated hospital course, increased hospital length of stay and total postoperative cost. A study shows that a low preoperative cerebral oximetry (rSO2) is associated with postoperative delirium after on-pump cardiac surgery. Another study showed that patients who underwent cardiac surgery with reduced cerebral blood flow (CBF) velocity in the left middle cerebral artery (MCA) preoperatively are at greater risk for postoperative cognitive dysfunction (POCD). Therefore, the investigators hypothesize that lower perioperative rSO2 and reduced preoperative mean flow velocity (MFV) of MCA are good predictors of the postoperative delirium in the patients undergoing the on-pump cardiac surgery.

Inclusion Criteria:

1. Patients in the study will be 60 or older undergoing elective major on-pump cardiac surgery

Exclusion Criteria:

1. No communication possible due to a language barrier or deafness
2. Patients diagnosed with neurocognitive disorders or psychiatric diseases (MMSE or Geriatric Depression Scale cannot be checked before surgery)
3. Patients with unstable hemodynamics or intubated before surgery
4. Patients diagnosed with significant (≥ 50%) intracranial stenosis confirmed by CT angiography or MR angiography
5. Patients diagnosed with stroke, TIA or neurologic diseases (e.g. Parkinson's disease, epilepsy, dementia, or taking psychiatric medications d/t psychiatric disorders)

patients undergoing on-pump cardiac surgery