Pre-incisional epidural magnesium provides pre-emptive and preventive analgesia in patients undergoing abdominal hysterectomy

Background. This prospective, randomized, double-blind study was designed to evaluate the pre-emptive and preventive analgesic efficacy of adding magnesium to a multimodal regimen of patient-controlled epidural analgesia (PCEA) in patients undergoing abdominal hysterectomy. Methods. Ninety patients were randomly assigned to one of the three groups. Pre-magnesium patients received bolus of magnesium 50 mg epidurally before induction of anaesthesia followed by infusion of 10 mg h(-1) until end of surgery. Post-magnesium patients received epidural saline during the same time periods plus bolus epidural magnesium 50 mg at the end of surgery. Patients in the control group received epidural saline during all three periods. Patients in the magnesium groups received PCEA with fentanyl 1 mu g ml(-1), bupivacaine 0.08%, and magnesium 1 mg ml(-1) after operation. Patients in the control group received PCEA with fentanyl 1 mu g ml(-1) and bupivacaine 0.08%. Data were recorded for three postoperative days. Results. There were significantly lower pain scores on rest or movement in the pre-magnesium group compared with the post-magnesium and control groups (P < 0.05). The daily analgesic consumption in the pre-magnesium group was significantly less than the other two groups (P < 0.05) and the dose consumed in the post-magnesium group was significantly smaller than the control group (P < 0.05). The groups were similar with respect to haemodynamic and respiratory variables, sedation, pruritus, nausea, and vomiting. Continuous epidural magnesium started before anaesthesia provided pre-emptive, preventive analgesia, and an analgesic-sparing effect that improved postoperative analgesia without increasing the incidence of side-effects.