The development of remifentanil-induced hyperalgesia (RIH) is an unpleasant experience for surgical patients. An alternative management, gradual withdrawal of remifentanil was effective in prevention of RIH. The investigators designed a simple modality to assess if under withdrawal of remifentanil and further drip-infusion of remifentanil immediately after extubation affected postoperative pain score, the requirement of rescue analgesics, and adverse effects.

In clinical practice, the gradual withdrawal of remifentanil during surgery is unsatisfied. Thus, the investigators conducted a simple modality in a single center retrospective cohort study to assess how under baseline gradual withdrawal of remifentanil and further drip infusion of remifentanil immediately after extubation affected postoperative pain score and use of analgesics.

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) score of I-III patients receiving total intravenous anesthesia

Exclusion Criteria:

• The use of inhalation agents or propofol combined with inhalation anesthesia
• Pregnancy
• Previous substance abuse
• Known allergies to opioids, propofol or any drugs used in the study
• History of neuropsychiatric disorder
• Age < 20 years or > 80 years

patients receiving surgery with age between 20-80 years

There is not a plan to make IPD available.