Intravenous Magnesium Sulphate During Spinal Anaesthesia and its Effect on Postoperative Analgesia in Lower Abdominal Surgery

Background: The implementation of multimodal or "balanced" analgesia strategies, which utilise non-opioid analgesics alongside opioid analgesics, has become standard in modern anaesthesia. Magnesium sulphate (MgSO₄) acts as an N-methyl-D-aspartate (NMDA) receptor antagonist and possesses antinociceptive properties. This study evaluated the analgesic efficacy and hemodynamic effects of intravenous MgSO₄ infusion in patients undergoing lower abdominal surgery under spinal anaesthesia. Material and Methods: In this randomized controlled trial, 96 patients were allocated into two groups: Group M was administered 50 mg/kg of MgSO₄ intravenously over 15 minutes, followed by a continuous infusion of 15 mg/kg/hr, while Group N received an equivalent volume of normal saline until the conclusion of the surgical procedure. Time to first rescue analgesic requirement, total analgesic requirement within 24 hours, visual analog scale (VAS) scores, Ramsay sedation scores, block characteristics, and hemodynamics were noted in both the groups. Results: Individuals in Group M had a markedly extended duration until the initial rescue analgesia (184.47 ± 12.60 min) in contrast to Group N (145.93 ± 11.18 min; p < 0.001). The overall Tramadol intake during a 24-hour period was markedly reduced in Group M (168.32±29.34 mg) in contrast to Group N (253.46±38.21; p = 0.001). Haemodynamic metrics were consistent across both cohorts. Conclusion: Perioperative intravenous magnesium sulphate infusion significantly enhances postoperative analgesia and reduces rescue analgesic requirements without adverse hemodynamic complications.

Keywords: Magnesium sulfate; Spinal anaesthesia; Postoperative analgesia; Visual analogue scale, Rescue analgesia.