Delirium occurs commonly in elderly patients. Its incidence after orthopedic surgery has been reported to be 5-61%. Delirium is classified into three sub-types: Hypoactive, hyperactive, and mixed. Although hyperactive delirium is not as common as hypoactive delirium, the abnormal behavior pattern of hyperactive delirium, such as agitation, confusion, or aggressiveness, is considered to be harmful to patients and medical personnel. Thus, it is important to promptly manage such behaviors associated with hyperactive delirium. Intraoperative sedation plays an important role in relieving anxiety or stress response of patients. Propofol-a common sedative agent-was reported to cause delirium more frequently, compared with dexmedetomidine, in post-cardiac surgery patients or mechanically-ventilated patients in the intensive care unit (ICU). In addition to the benefits of reducing opioid consumption and postoperative nausea/vomiting, dexmedetomidine is most often used for ICU sedation or procedural sedation. However, there has not been any prospective randomized study investigating how intraoperative dexmedetomidine sedation during regional anesthesia affects postoperative consciousness, perception, memory, behavior, emotion, and so on. In this study, based on the hypothesis that intraoperative dexmedetomidine sedation may reduce the incidence of abnormal psycho-motor behavior compared with propofol sedation, investigators prospectively will investigate the incidence of postoperative delirium in elderly patients who undergo orthopedic surgery with regional anesthesia.

Inclusion Criteria:

• Patients who undergo orthopedic surgery under spinal anesthesia
• Patients who want to sedation during the surgery
• Age of 65 years or greater
• American Society of Anesthesiologists physical status classification 1 and 2

Exclusion Criteria:

• General anesthesia
• Age < 65 years
• Patients who do not want to sedation during the surgery
• Patients who do not receive patient controlled analgesia postoperatively.
• Cognitive disorders
• Central nervous system disease, including dementia and Parkinson's disease