Postoperative delirium is an important problem in patients undergoing major surgery. The incidence of delirium was 12.5% in the patients over 70 years old undergoing spine surgery. A study shows that a low preoperative regional cerebral oxygen saturation (rSO2) is associated with postoperative delirium after on-pump cardiac surgery. This same perturbation likely also increases the risk for postoperative delirium after spine surgery, although there are little data that have evaluated this hypothesis. Therefore, this observational study was designed to explore the relationship between perioperative rSO2 and the delirium in elderly patients undergoing spine surgery.

Inclusion Criteria:

1. Patients in the study will be 60 or older undergoing elective major spine surgery (expected operative time is more than 2 hrs).
2. Patients who can do the mini-mental state examination (MMSE), Confusion Assessment Method for the ICU (CAM-ICU) and Intensive Care Delirium Screening Checklist (ICDSC).
3. Patients who understand the nature of the study and are willing to sign the consent form

Exclusion Criteria:

1. Emergency surgery
2. Patients diagnosed with neurocognitive disorders or psychiatric diseases, thus, cannot check MMSE or communicate with other people (e.g. Alzheimer's dementia, alcohol abuse)
3. Patients diagnosed with cerebrovascular disorders (e.g. stroke, atherosclerotic stenosis of carotid artery, TIA)
4. Patients who cannot be followed up until 2 days after surgery

patients undergoing spine surgery