Postoperative epidural analgesia (EA) is an effective and well-accepted modality of pain relief technique after having total knee replacement operation(1,4). Patient controlled epidural analgesia (PCEA) has been shown to be safe and effective in standard ward setting(2) and results in reduced epidural analgesic requirements(3). Besides, it also bear the advantage of avoidance of overdose, reduction of waiting times and involvement of patients in their analgesic regimen(3). Both ropivacaine and levobupivacaine are the local anaesthetic using in epidural analgesia which has been proven to be safe and effective(4). 0.2% Ropivacaine with 2ug/ml fentanyl has been used in our locality for more than 8 years. Another local anaesthetics, levobupivacaine, a S-enantiomer of bupivacaine has come up in Hong Kong, which has been proved to be safe, effective and may be better value for money. These two drugs has been proven to have similar analgesic potency in using as EA for postoperative pain relief for other operation(5,6,7) and for orthropaedics operation but in different concentration(4). Concerns have been raised about the introduction of the levobupivacaine in the departmental protocol. Objectives of this study are A)to determine the equivalence of two local anaesthetics regimen ; 0.2% ropivacaine with 2ug/ml fentanyl and 0.2% levobupivacaine with 2ug/ml fentanyl and B) to assess the cost-effectiveness of using these two regimens.

The null hypothesis is that the difference of analgesic effect, presented with visual analogue score, of two patient controlled epidural analgesia regimen, the 0.2% ropivacaine with 2 ug/ml fentanyl and 0.2% levobupivacaine with 2ug/ml fentanyl is higher than the threshold of 9 mm VAS. (8,9,10)

Inclusion Criteria:

• > 18 years old, ASA I -III and
• Undergoing total knee arthroplasty
• Combine spinal-epidural anaesthesia

Exclusion Criteria:

• Known hypersensitivity to amide-type local anaesthetics
• Known hypersensitivity to opioids
• Known history of severe cardiovascular, renal, hepatic, neurological or psychiatric disease as judged by the investigator
• Known history of peripheral neuropathies
• Those receiving chronic analgesic therapy, or any contraindication for epidural analgesia (e.g. clotting disorders, or history of lumbar surgery)
• Inability to perform a pain score, or pregnancy or lactation