<qa>  What is the incidence of delirium in patients over 70 years old?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. 