This study aims to investigate the potential association between pain sensitivity questionnaire score, the severity of postoperative pain, and postoperative analgesic requirement in patients with open colorectal cancer surgery. This information may be used to guide the optimal postoperative pain management, and ultimately improve patient's quality of life.

We plan to investigate the predictive ability of the PSQ as well as experimental parameters of pain sensitivity using electronic algometer and other known risk factors for postoperative pain in 100 patients scheduled for open colorectal cancer surgery.

The following items are investigated before surgery; Age, sex, level of education, type of surgery, past surgical history, presence of chronic pain, the expected maximal pain score (VAS) after surgery, Pain catastrophizing scale, anxiety scale (HADS-A), Pain sensitivity questionnaire, and pain threshold measured by electronic algometer.

The total opioid consumption is investigated for 24 and 48 hours after surgery. In addition, the severity of postoperative pain is measured by the 11-point VAS at 24 and 48 hours after surgery. Patient satisfaction with postoperative pain control is also investigated at 48 hours after surgery using the 7-point patient's satisfaction scale.

Inclusion Criteria:

• Age 18 years or above
• Patients scheduled for open colorectal cancer surgery under general anesthesia
• ASA status I-III
• Ability to read and understand the information sheet, questionnaires, and the - consent form
• Patients scheduled for using IV-PCA after surgery

Exclusion Criteria:

• Unable to read and understand the information sheet, questionnaires, and the consent form
• Severe medical or psychological diseases
• Patients with preoperative chronic pain