A randomized controlled trial to evaluate the effect of addition of epidural magnesium sulphate on the duration of postoperative analgesia in patients undergoing lower abdominal surgeries under epidural anaesthesia

Background: Noxious stimuli release excitatory neurotransmitters such as glutamate and aspartate, which bind to various receptors including N-methyl-D-aspartate (NMDA) receptors. Magnesium is a NMDA antagonist and has antinociceptive effects in animal and human models of pain. The addition of magnesium to postoperative epidural infusion may decrease postoperative pain and requirement of opioids. Methods: Sixty patients undergoing elective total abdominal hysterectomies were enrolled to receive either 1ml of magnesium sulfate (50 mg/ml) (Group M) or 1 ml of saline (Group C) in the epidural anaesthetic solution (9ml of 0.125% bupivacaine) for postoperative analgesia. Fentanyl 1µg/kg was given epidurally as rescue analgesia. Haemodynamic parameters, pain assessment using a visual analogue scale (VAS), and fentanyl consumption were recorded in the postoperative period. Results: There was significant difference between groups in the time to first analgesic requirement. Compared with Group C, patients in Group M received smaller doses of epidural fentanyl (P< 0.001). The cumulative fentanyl consumption in 24 h was significantly lower in Group M (119±56 mg) as compared to Group C(267.8± 92 mg)(P < 0.001). Patients in Group M had less pain as measured via VAS score in the first hour of the postoperative period (P < 0.001). The groups were similar with respect to haemodynamic and respiratory variables, sedation, pruritus, and nausea. Conclusion: Administration of magnesium to epidural local anaesthetic solution provides longer duration of postoperative analgesia and reduced postoperative fentanyl consumption without added side-effects.DOI: http://dx.doi.org/10.4038/slja.v21i1.4435