90 female patients aged between 18 and 65 years, scheduled for cancer breast surgeries will be assigned to 2 groups, each of 45. Group (K) will receive a bolus of 0.5 mg/kg ketamine with induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour continued till 24 hours after surgery. Group (KM) will receive a bolus of 0.5 mg/kg ketamine added to 50mg/kg magnesium sulfate over 30 minutes after induction of anaesthesia, followed by ketamine infusion 0.12 mg/kg/hour added to 8mg/kg/hour of magnesium sulfate continued till 24 hours after surgery. The same anaesthetic regimen will be applied to all patients. Total intraoperative fentanyl required to maintain mean blood pressure within 20% of its baseline will be recorded. After surgery, all patients will be connected to PCA device containing morphine solution, the amount of morphine consumed during the first 24 hours will be recorded. In the follow-up visits after 3 months, all patients will be assessed for neuropathic pain by DN4 questionnaire.
