Intrathecal epinephrine has been known to increase the duration of spinal anesthesia, or increase the quality of anesthesia. However, there is still a controversy, and the mechanism of epinephrine is recently suggested as a modulator of pain information in the spinal cord. Therefore, the investigators try to investigate the dose sparing effect of intrathecal epinephrine for spinal anesthesia with bupivacaine.

For patient undergoing total knee replacement arthroplasty, patients injected intrathecally with bupivacaine 8 mg were compared with those with bupivacaine 8 mg with 25 mcg of epinephrine, bupivacaine 8 mg with 50 mcg of epinephrine, and those with bupivacaine 8 mg with 100 mcg of epinephrine. The investigators compared the characteristics of spinal anesthesia including the quality and complication of spinal anesthesia. The researchers investigated whether intrathecal dose of epinephrine can reduce bupivacaine requirement and this effect is dependent on the dose of epinephrine.

Inclusion Criteria:

• patient undergoing total knee replacement arthroplasty

Exclusion Criteria:

• patient with cardiac or pulmonary disease (ASA class III or more)
• patient undergone previous spine surgery
• patient undergoing revised knee replacement