This prospective randomized double-blind dose-response study is aimed to investigate the ED50 and ED95 of intrathecal bupivacaine with or without epinephrine 100 mcg for total knee replacement arthroplasty.

Patients undergoing total knee replacement arthroplasty are randomly assigned to six bupivacaine dose group (6, 7, 8, 9, 10, 11 mg). Combined spinal-epidural anesthesia would be performed. The dose would be considered as successful if no epidural supplement was required during surgery. A probit analysis will be performed to calculate the ED50 and ED95 of intrathecal bupivacaine with or without epinephrine for total knee replacement arthroplasty.

After these measurements, ED50 and ED95 of bupivacaine with epinephrine would be compared with those without epinephrine.

Inclusion Criteria:

• The patients with ASA class I or II scheduled for total knee replacement surgery

Exclusion Criteria:

• Patients with previous spine surgery, diabetic and other neuropathy, skin infection at the site of injection, allergy to bupivacaine and other common contraindications for spinal anesthesia were excluded from this study.