All patients will be screened to determine eligibility for study entry, and the patients who meet the eligibility requirements will be informed about the study and potential risks. After giving written informed consent, the patients will be randomized into different doses of dexmedetomidine groups and the comparative groups in a same ratio.
The purpose of this study is to find out appropriate dose range of dexmedetomidine to provide the elderly patients satisfactory sedation and analgesia with stable hemodynamics during perioperative period of hip replacement under general anesthesia.