Evaluation of single epidural bolus dose of magnesium sulphate as an adjuvant to fentanyl for postoperative analgesia in total knee replacement surgery

Background: Magnesium has antinociceptive effects in animal and human models of pain. Magnesium has been used as an adjuvant by various routes, including intravenous, intrathecal and epidural in different dosage regimens. Forty patients undergoing Total Knee Replacement surgery were enrolled to receive either fentanyl (Group F) or fentanyl plus magnesium sulphate (Group FM) post operatively for epidural analgesia. Ventilatory frequency, heart rate, blood pressure, pain assessment using a visual analogue scale (VAS), sedation scores and fentanyl consumption were recorded in the postoperative period. This is a prospective, randomized, controlled study designed to assess the efficacy of single bolus administration of Magnesium epidurally as an adjuvant to epidural fentanyl for postoperative analgesia taken in National Institute of Medical Science, Jaipur. Materials and Methods: 40 Patients of ASA grade I and II aged 20 to 60 years of either gender undergoing Total Knee replacement surgery enrolled in study received combined spinal epidural anaesthesia with 4 ml of 0.5% hyperbaric bupivacaine intrathecally. After surgery patients were randomized into group F (epidural fentanyl 50μg in 10ml saline) and Group FM (epidural magnesium 75 mg along with fentanyl 50μg in 10 ml saline). Rescue analgesic is provided by Intravenous Tramadol if VAS score >4. Patient’s first analgesic requirement time and duration of analgesia were recorded. The groups were similar with respect to haemodynamic and respiratory variables, sedation, pruritis, and nausea. Co-administration of magnesium for postoperative epidural analgesia results in a reduction in fentanyl consumption without any side-effects. Result: Magnesium, the fourth most common cation in the body, has postsynaptic N-methyl Daspartate (NMDA) calcium channel blocker properties, and has been used successfully to potentiate opioid analgesia and to treat neuropathic pain. The duration of analgesia was significantly longer for Group FM compared to Group F. The frequency of rescue analgesics required in postoperative period in group FM was significantly less than that in Group F. Conclusion: The administration of magnesium as an adjuvant to epidural fentanyl for postoperative analgesia results in significantly lower VAS with prolonged duration of analgesia as compared to epidural fentanyl alone. Thus, Epidural magnesium was found to reduce the use of postoperative analgesia without increases in side.