Comparison of Butorphanol and Tramadol Associated Patient-Controlled Analgesia (PCA) After Hysterectomy

Inclusion Criteria: * ASA physical status I-II * Chinese * 19-64yr * Uterus myoma Exclusion Criteria: * Allergy to opioids, a history of the use of centrally-acting drugs of any sort, chronic pain and psychiatric diseases records. * Participants younger than 18yr，older than 65yr or pregnancy was eliminated. * Due to the significant changes in vital signs might affect cognition of pain and that of sensation, over 20% variation of these records from the baselines or below 92% of SpO2 under 20-40% nasal tube oxygen at any time should be excluded from the study. * Those who were not willing to or could not finish the whole study at any time. * Any patient who exhibited a combative or incoherent state of PCA analgesia would be excluded from the study. * Allergy to local anesthetics. * Failed to perform the epidural catheterization. * Those who demonstrated significant nerve-associated side effects from the insertion of the epidural needle.