Numbers of postoperative PCA related side effects among three groups will be determined by comparing and analyzing frequency distributions. To determine whether the patients with hypertension require less post operative opiate analgesics than others, multivariate analysis with repeated measures will be performed to identify the major and the minor factors predicting the use of postoperative pain therapy. The major aim of the study is to test the hypothesis that the morphine comsumpted by the hypertension group is less than those of the normotension group. The minor aims for the study are the difference related to pain intensity, or the incidence of side effects among groups.

Inclusion Criteria:

• 300 eligible subjects
• No contraindication for inhalation anesthesia
• Elective surgery
• Age between 20-75 y/o
• No contraindication for postoperative morphine pain control
• Female or male
• Essential hypertension stage I and II (140<=SBP<=180; 90<=DBP<=110)

Exclusion Criteria:

• Liver disease
• Renal disease
• Those who is presumed to go to ICU after surgery
• The patients with dementia or conscious disturbance
• Pregnancy or breast feeding
• Secondary hypertension
• events in recent 6 months myocardial infarction cardiac bypass surgery unstable angina cerebrovascular events congestive heart failure significant arrhythmia thoracic surgery

Those patients enrolled will be divided into three groups as follows As the treatment and choice of drugs for hypertension is complex but internation guideline-oriented. We would like to enroll enough sample size in the hypertensive groups and subgroups.

1. Normaltension group (control group)
2. Hypertension without treatment
3. Hypertension with treatment as follows (according to subject's daily routine Tx, the PI not involved into the choice and further manitence of drugs) I. Hypertension with treatment with ACEI II. Hypertension with treatment with β blocker III. Hypertension with treatment with Ca channel blocker IV. Hypertension with treatment with diuretics