Uterine curettage is usually performed under the anesthesia of propofol-fentanyl or para-cervical block,of which generally has significant incidence of respiratory depression which increases the demand on intraoperative monitoring, or has unavoidable insufficient blockade which results in intraoperative suffering of pain. Butorphanol is an analgesic with combined effects on mu and kappa opioid receptors leading to a role as analgesia and sedation. The investigators hypothesized that combined propofol with butorphanol during uterine curettage would produce optimal effectiveness of these two drugs by adding sedative and analgesic effects together. In addition, it would decrease the intraoperative consumption of propofol without increase the incidence of side effects. Furthermore, such combination would alleviate postoperative pain.