All consenting patients will be randomised to one of two groups, the epidural pethidine group (group P) or the placebo group (group N). All patients will receive fentanyl 2 - 3 mcg/kg intra-operatively as part of a balanced anaesthesia. Otherwise the anaesthesia will not be controlled. At the conclusion of surgery, all patients will have an epidural catheter placed under direct vision by the consultant surgeon. In the recovery room, all patients will have a patient-controlled analgesia (PCA) machine attached to the side arm of the intravenous infusion line. All participants will receive written as well as standard verbal instruction on the use of the PCA. The 30 ml PCA syringe will contain pethidine 10 mg/ml saline. Patients will be given standard instructions on the use of the PCA machine. The PCA machine will be set to deliver a one millilitre bolus with a five minute lockout, and a maximum dose of 20 ml (200 mg) over four hours. In addition, an infusion will be connected to the epidural catheter, containing either pethidine 250 mg in 250 ml saline (group P) or saline 250 ml (group N). The infusion will be commenced at 10 -20 ml/h according to the preference of the attending anaesthetist. This will generally depend on the age and weight of the patient.