Object: Every person's pain perception and possible postoperative pain is different. As the investigators know, they are affected by many factors. However, the investigators don't know whether the smoking factors, alcohol factors, surgery type, education background, etc. will affect individual pain perception and possible postoperative pain in Chinese population. This study was conducted to investigate the power of these possible affect factors. Method: Patients receiving elective surgery under general anesthesia were recruited into this study. The investigators measured their preoperative pressure pain threshold (PPT) and pressure pain tolerance (PTO)and also investigated the patient's personal information of smoking factors, alcohol factors, surgery type, education background, etc. In addition, we retrospectively investigated the visual analog scale (VAS) during patient-controlled analgesia (PCA) treatment 0 to 48 h after operation as well as the PCA press frequency and drug consumption of those patients who received PCA administration.

Patients with the following diseases were excluded: known history of chronic pain, psychiatric diseases or communication disorders, diabetes mellitus, severe cardiovascular diseases, kidney or liver diseases with poor hepatic function, alcohol or pregnancy or at the lactation period.

Inclusion Criteria:

• Aged 18 to 70
• The right hand is handedness
• Agreed to participate the research
• Not with known chronic disease
• Not taking analgesics within 3 months

Exclusion Criteria:

• History of chronic pain diseases
• Diabetes mellitus
• Severe cardiovascular diseases
• Kidney or liver diseases
• Alcohol or drug abuse
• Pregnancy or at lactation period
• Disagree to participate to the research

Chinese patients receiving elective surgery under general anesthesia