Intravenous patient-controlled analgesia (PCA) is a popular technique for postoperative pain management. Although several drugs are recognized as effective therapeutic options, optimal selection of drugs in hysterectomy patients underwent different anesthesia treatments remains unknown explicitly. The investigators hypothesized that butorphanol and tramadol can produce different analgesic effects with intravenous PCA after abdominal 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.