Tourniquet is widely used in orthopedic surgery. However, prolonged tourniquet inflation may cause a gradual rise in blood pressure, which named as tourniquet-associated hypertension. Thus, to effectively prevent the tourniquet related hemodynamic responses is important for patients receiving limb surgery.

Tracleer is an endothelin receptor antagonist indicated for the treatment of pulmonary arterial hypertension. Tracleer can also be used to treat retistant hypertension. At present trial, the investigators are going to investigate the effect of Tracleer on tourniquet-associated hypertension during total knee arthroplasty.

At present study, the investigators will use endothelin receptor antagonist, Tracleer (Bosentan), to investigate the effect of Tracleer on tourniquet-associated hypertension during unilateral total knee arthroplasty, and evaluate its safety and effectivity. The purpose of this study is to find a new therapy to prevent and treat tourniquet-associated hypertension.

Inclusion Criteria:

• Patients underwent selected total knee arthroplasty under general anesthesia
• ASA II-III
• 18~65 years old
• Signed informed consent voluntarily

Exclusion Criteria:

• Do not apply tourniquet during the surgery
• Patients underwent emergency surgery
• Having applied tourniquet in last three months
• Patients underwent bilateral total knee arthroplasty
• Dysfunction of liver or kidney
• Anemia (Hb <90 g/L)
• Serious myocardial disease (eg. coronary heart disease, heart failure, severe arrhythmia)
• Coagulation disorder
• Diabetic
• Leukocyte higher than normal value
• Pneumonia, asthma, chronic obstructive pulmonary disease
• Hypotension before surgery (systolic pressure < 90 mmHg)
• Pregnant woman or puerpera
• Having being enrolled in other clinical trial in last 3 months