Effect of Magnesium Sulphate on Anaesthetic Agent Requirements Under BIS-targeted Anaesthesia and Postoperative Analgesia: A Prospective Randomised Controlled Study

Introduction: Administration of an appropriate dose of anaesthetic drug and simultaneously achieving adequate depth of anaesthesia with minimal side effects is a challenge. Magnesium Sulphate (MgSO4 ) significantly reduces the requirements of anaesthetic agents. Aim: This study aimed to evaluate the impact of MgSO4 on requirements of propofol, vecuronium, and sevoflurane under Bispectral Index (BIS) guidance, along with associated changes in haemodynamic parameters and postoperative analgesia. Materials and Methods: The present prospective randomised double-blinded controlled study was conducted at Medical College and SSG Hospital, Vadodara, Gujarat, India, from November 2019 to October 2020. It was carried out among 100 patients undergoing elective tympanomastoidectomy under GA. Group M received MgSO4 40 mg/kg, and Group N received normal saline. Both groups received fentanyl 2 µg/kg as premedication. Induction was carried out using propofol infusion at 30 mg/kg/hr and was stopped at a BIS index of 40-50. Following intubation with succinylcholine, maintenance of anaesthesia was achieved using O2 + N2 O, sevoflurane and vecuronium, targeting a BIS index between 40 and 60. The primary parameters assessed included total propofol requirement for induction, intraoperative requirement of vecuronium and sevoflurane, haemodynamic variables {Heart Rate (HR), Mean Arterial Pressure (MAP)} and postoperative analgesic requirement. Haemodynamic variables were recorded at baseline (preinduction), during induction, immediately after intubation, every five minutes for the first 15 minutes, and then every 15 minutes until the end of surgery. Postoperative analgesia was assessed using Visual Analog Scale (VAS) scores at 0, 1, 2, 4, 6, and 12 hours, postoperatively. Statistical analysis was performed using the student’s t-test for normally distributed data and the Mann-Whitney U or Kolmogorov-Smirnov test for non-normally distributed data, with a p-value of <0.05 considered statistically significant. Results: The requirement of propofol was 101.6±21.21 mg in Group M while it was 141.6±14.14 mg in Group N (p<0.0001). Vecuronium requirement in Group M was 5.48±0.707 mg and in Group N it was 6.7±1.414 mg (p<0.0001). Sevoflurane consumption was 37.16±9.03 mg in Group M and 46.25±8.84 mg in Group N (p<0.001). The average duration of analgesia was 10.72±3.85 hours in Group M and 7±2.36 hours in Group N (p<0.0001). The number of rescue analgesia were less i.e., 1.44±0.54 in Group M than Group N which was 2.02±0.58 (p<0.0001). Conclusion: Magnesium Sulphate in GA significantly reduces the requirement of propofol, vecuronium and sevoflurane while maintaining BIS value of 40 to 60 with satisfactory postoperative analgesia.