Comparison of Levobupivacaine and Ropivacaine for Femoral Neural Block

Primary objective The primary aim of this study is to measure the molar of levobupivacaine and the molar median effective dose of ropivacaine when administered as a femoral perineural infusion to prevent pain 30 hours after total knee replacement Secondary objectives

To assess the:

Degree of postoperative pain, need for rescue analgesia,side effect profile of both groups, self-efficacy, expectancy, quality of life / health economics Type of study: Prospective single blind randomised controlled trial Planned number of subjects: 48 Study duration: 24 months Randomisation procedures Following informed consent, participants will be randomised into two groups. All preparations for study will be coded so that participants have an equal chance of receiving one of the two local anesthetics. Randomisation will be carried out by computer program, and codes kept in pharmacy in a sealed envelope.

Protocol for patient management Preoperative - Anaesthetic room Antibiotics: augmentin 1.2 grams Sedation with Target Controlled Infusion of propofol at plasma level of 0.5 micrograms per millilitre (μg.ml-1) Spinal anaesthesia with 3.2 ml hypobaric "plain" bupivacaine 0.5% and intrathecal morphine 0.1 mg All regional nerve blocks performed under ultrasound control Femoral block: 15 ml 0.3% levobupivacaine or ropivacaineFemoral perineural catheter inserted by Anaesthetist 5cm in a cranial direction Sciatic block: single injection 12 ml 0.5% levobupivacaine or ropivacaine Obturator block: single injection 6 ml 0.5% levobupivacaine or ropivacaine

Postoperative 8 hour anaesthetic observation

Determine median effective dose of levobupivacaine and ropivacaine for anaesthesia 8 hours after insertion of spinal needle, resolution of spinal anaesthesia confirmed and verbal rating pain score of knee bending recorded. Clinical measurement and subsequent patient dosing is as follows:

1. "Anaesthetic success": verbal rating pain score = 0: Next patient receives 10 microMolar (μM) less of levobupivacaine or 10μM ropivacaine.
2. "Anaesthetic failure": verbal rating pain score ≥ 1. Resolved by rescue analgesia of 15ml, 150μM levobupivacaine (5.8ml, 0.75%) or 15ml, 150μM ropivacaine (6.2ml, 0.75%).Next patient receives 10μM more of levobupivacaine or 10μM ropivacaine.
3. Technical failure: verbal rating pain score ≥ 1 Not resolved by rescue analgesia of 15ml, 150μM levobupivacaine (5.8ml, 0.75%) or 15ml, 150μM ropivacaine (6.2ml, 0.75%.Next patient receives same mass levobupivacaine or ropivacaine.

After the 8 hour assessment, all patients (excluding technical failures but including "anaesthetic failures") will start a femoral perineural infusion with levobupivacaine or ropivacaine at a rate of 10ml h-1 and concentration of 1(microMolar per millilitre) μM.ml-1 (400μM in 400ml elastomeric ball) for 48 hours.Patients classed as "technical failure" will have a femoral perineural catheter reinserted.

Postoperative 30 hour (±2hour) anaesthetic observation

The postoperative 30 hour anaesthetic observation will only be performed on the "anaesthetic successes" from the 8 hour observation. The median effective dose of levobupivacaine and ropivacaine for analgesia will be determined by choosing an end point of verbal rating pain score 0 at 30h after the start of spinal anaesthesia. Patients will divide into three groups:

1. "Successful pain relief" verbal rating pain score = 0 Next patient receives 10μM less of levobupivacaine or 10μM ropivacaine.
2. "Unsuccessful pain relief" verbal rating pain score ≥ 1 resolved by rescue analgesia of 15ml, 50μM levobupivacaine (5.8ml, 0.25% + saline) or 15ml, 50μM ropivacaine (7.7ml, 0.20% + saline).Next patient receives 10μM more of levobupivacaine or 10μM ropivacaine.
3. Technical failure: verbal rating pain score ≥ 1. Not resolved by rescue analgesia of 15ml, 50μM levobupivacaine (5.8ml, 0.25% + saline) or ml, 50μM ropivacaine (7.7ml, 0.20% + saline).

Rescue analgesia Rescue will be standardised: 15ml, 50μM levobupivacaine (5.8ml, 0.25% + saline) or 15ml, 50μM ropivacaine (7.7ml, 0.20% + saline). The number of rescue administrations will be counted.

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