• Sonali Banwait, Sujata Sharma, Mridula Pawar, Rakesh Garg, and Rajesh Sood.
• Department of Anaesthesiology and Intensive Care, Postgraduate Institute of Medical Education and Research and Dr. Ram Manohar Lohia Hospital, New Delhi, India.
• Saudi J Anaesth. 2012 Jul 1;6(3):273-8.

ObjectiveMagnesium has been used as an adjuvant by various routes, including intravenous, intrathecal, and epidural in different dosage regimens. The effect of single bolus dose of magnesium as an adjuvant to fentanyl for postoperative analgesia has not been studied. This prospective randomized controlled trial was done to evaluate the efficacy of single bolus administration of magnesium epidurally as an adjuvant to epidural fentanyl for postoperative analgesia in patients undergoing total hip replacement under combined spinal epidural anesthesia.MethodsSixty patients received combined spinal-epidural anesthesia with 2 mL of 0.5% hyperbaric bupivacaine intrathecally. After the surgery, patients were randomized into Group F [epidural fentanyl (1 μg/kg) in 10 mL saline] and Group FM [epidural magnesium (75 mg) along with fentanyl (1 μg/kg) in 10 mL saline]. Supplementary analgesia was provided by 50 mg intravenous tramadol if Verbal Rating Score (VRS) >4. Patient's first analgesic requirement and duration of analgesia were recorded.ResultsThe duration of analgesia was significantly longer for Group FM, 340±28.8 min, compared with Group F, 164±17.1 min (P=0.001). The frequency of rescue analgesics required in 24-h postoperative period in Group FM (2.3±0.5) was significantly less than that in Group F (4.3±0.5) (P=0.001). VRS was significantly lower in Group FM up to 4 h in the postoperative period (P=0.001). Bromage scale was statistically insignificant at all points of time.ConclusionsThe administration of magnesium (75 mg) as an adjuvant to epidural fentanyl (1 μg/ kg) for postoperative analgesia results in significantly lower VRS with prolonged duration of analgesia as compared with epidural fentanyl (1 μg/kg) alone. Concomitant administration of magnesium also reduces the requirement of breakthrough analgesics with no increased incidence of side effects.

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