Trial to Compare Femoral Nerve Block With Local Anaesthetic Injection for Post-operative Pain After Knee Replacement.

Supine position If using peripheral nerve stimulator for localisation of the femoral nerve: 50 mm insulated needle Peripheral nerve stimulator set at 2 Hz with pulse width 100μs When quadriceps muscle twitch is present with a stimulated current between 0.2 and 0.5mA, inject 20ml 0.375% (3.75mg/ml) Levo- bupivacaine If using ultrasound for localisation of the femoral nerve: High frequency linear array probe Short bevelled nerve-block needle, using in or out of plane technique Inject 20ml 0.375% (3.75mg/ml) Levo-bupivacaine underneath fascia iliaca ensuring adequate spread of local anaesthetic

Local infiltration analgesia to be administered by surgeon towards the end of operation: 40ml of bupivacaine 0.25% with adrenaline 1:200 000, diluted to 150ml with saline 0.9%. This is then divided into thirds; 50ml into the posterior capsule before cementing, 50ml into the medial and lateral capsules and 50ml into subcutaneous tissues and in and around the vastus medialis and sartorius muscles (where it may block the saphenous nerve).

Patients in both arms of the trial will be given sub arachnoid anasthesia of 2.5-3.0ml of plain bupivacaine 0.5% using a 25G Whitacre needle. Patients may have 0-4mg midazolam and/or 0-1mcg/kg fentanyl and/or 0-4mcg/ml propofol sedation using the Marsh protocol if required for this procedure as deemed appropriate by the anaesthetist.

After insertion of the sub arachnoid anaesthesia the patient may choose to be fully asleep or sedated. If they choose to be fully asleep, they may have up to 2mcg/kg fentanyl in total (including any given at time of subarachnoid injection), muscle relaxation as indicated for facilitation of intubation where needed, airway control using LMA or tracheal tube where needed, and general anaesthesia maintained using inspired oxygen concentration of 0.3-0.7 with propofol up to 5mcg/kg (Marsh protocol) or isoflurane or sevoflurane. If the patient chooses to have sedation they may have additional midazolam up to a total dose of 4mg and/or a propofol infusion (Marsh protocol) of 0-4mcg/ml.

All patients will receive 1g paracetamol pre-operatively. Those on non steroidal anti inflammatory drugs may continue to take them. Apart from these, no other pain relieving pre-medications are to be used. Patients may be given anxiolysis using temazepam 10-20mg or diazepam 2-5mg by mouth if required. Antacid premedication is permitted using ranitidine, metoclopramide or proton pump inhibitors.

If paracetamol has not been given pre-operatively, it will be given intraoperatively 1g IV. Where 2 or more of the following risk factors are present; female, non smoker, previous post operative nausea or vomiting, intra operative opiates, the patients will be given 4mg dexamethasone and or 4mg ondansetron IV. Vasopressor drugs may be given at the anaesthetist's discretion to maintain an appropriate blood pressure. Intraoperative fluid infusion is at the discretion of the anaesthetist. Antibiotic prophylaxis is as per the hospital protocol (currently 6mg/kg Teicoplanin IV and 3mg/kg gentamicin pre induction). Tranexamic acid will be given as per unit protocol, (currently 1g pre-operatively IV and 500mg orally at 8 hours post op. unless contraindicated by a high risk of thrombosis.)

Patients will all be given a morphine pump which will give 1mg every 5 minutes. This is to be discontinued after 48 hours and changed to oral morphine 10-20mg if weight 50-70kg, 20-30mg if weight \>70kg 2 hourly.

All patients will be given 1g paracetamol 6 hourly and 400mg ibuprofen 8 hourly unless there are contraindications. If patients are on an alternative non-steroidal anti inflammatory drug then this may be substituted for ibuprofen.

All patients will receive 4mg ondansetron regularly for 2 days. They will be prescribed 50mg cyclizine as an addition to this if needed.