Evaluation of Pharmacogenetic Factors Affecting Fentanyl Requirements for Postoperative Pain Control

Inclusion Criteria: * Patients undergoing total abdominal hysterectomy (TAH) or laparoscopy assisted vaginal hysterectomy (LAVH) under general anesthesia * Patients who want to use intravenous patient controlled analgesia (PCA) after surgery * ASA physical status class I, II Exclusion Criteria: * history of drug addiction * opioid medication within 12 hours before surgery * previous history of opioid medication for 3 months * neurologic disorder * cardiac disorder * hepatic disease * renal disease * respiratory disease such as COPD, asthma * sleep apnea * BMI \> 30 * psycotic disorder