Numbers of postoperative PCA(Patient-Controlled Analgesia) related side effects among current, past and non smokers are determined by comparing and analyzing frequency distributions. To determine whether smokers require more post operative opiate analgesics than others. Multivariate analysis will be performed to identify the major and the minor factors predicting the use of postoperative pain therapy. Our previous related study showed that the smoker male patients consumed more analgesics than those without smoking, but the female group showed the similar findings. However, the case number, especially the female cases, is underpowered. Investigators hope to increase the case number to have a better statistical and clinical significance.

Inclusion Criteria:

• Patients undergoing elective general surgery are assigned to current smokers（n=100） or past smokers（n=100） or never smokers（n=100） according to the questionnaires "Fagerstrom test for nicotine dependence" 1 day prior to the surgery.

Exclusion Criteria:

• the patients undergoing major thoracic cardiovascular surgery
• the patients with significant lung lesion
• the patients with conscious disturbance
• the patients with allergic history to morphine