Pain Relief After Colorectal Surgery: Spinal Combined With Painbuster® vs Painbuster® Alone.

This is a pilot randomised controlled trial Hypotheses - Following colorectal surgery, spinal anaesthesia combined with a continuous infusion of local anaesthetic into the surgical wound provides 1. better pain relief 2. a reduced stress response when compared to the use of continuous infusion of local anaesthetic into the surgical wound alone. Patients undergoing surgical resection for colorectal cancer will be randomised to receive either 1. A single shot of spinal anaesthesia plus a continuous infusion of local anaesthetic into the surgical wound or 2. Continuous infusion of local anaesthetic into the surgical wound Spinal Anaesthesia The spinal anaesthetic (SA) with be placed after commencement of general anaesthesia this will ensure the patients remain blinded to the intervention. SA will be performed in the lateral position using a midline approach. L3/4 interspace will be identified using Tuffier's as the anatomical landmark. After confirmation of correct placement using a 25G Whitacre needle, 12.5 mg of hyperbaric Bupivacaine in a mixture with 500mcg Diamorphine will be injected intrathecally. Infusion of local anaesthetic The catheter through which the infusion of local anaesthetic will be given, will be placed by the surgeon at the end of the procedure in a location determined by the surgical approach. A bolus dose of 20ml 0.25% L-Bupivacaine will be injected down the catheters prior to the connection of the elastomeric pump which will also contain 270ml 0.25% L-Bupivacaine General anaesthesia will be managed in the same way for both groups