Effect of Low Dose Intravenous Magnesium Sulphate on Sensory Regression Time in Patients undergoing Spinal Anaesthesia- A Randomised Placebo-controlled Double-blinded Study

Introduction: Adjuvants like intravenous (i.v.) Magnesium Sulphate (MgSO4) are used to improve the efficacy and duration of spinal anaesthesia and postoperative analgesia. But it is unclear, whether this prolongation of duration of analgesia is an independent effect of MgSO4 or it is because of increased duration of spinal anaesthesia itself.

Aim: To evaluate the effect of intraoperative i.v. low dose MgSO4 on two-segment regression time of sensory block, regression time up to L2 dermatome from the highest level of sensory block and postoperative analgesic requirement.

Materials and Methods: This randomised placebo-controlled blinded study was conducted in the Department of Anaesthesia, Fakhruddin Ali Ahmed Medical College and Hospital, Barpeta, Assam, India from September 2020 to August 2021. A total of 60 patients, satisfying American Society of Anaesthesiology (ASA) physical status I and status II, aged between 40-70 years, patients undergoing femur fracture surgery under spinal anaesthesia were enrolled in the present study. Patients in the magnesium group (Group M, n=30) received MgSO4 5 mg/kg infusion, and control group (Group C, n=30) received at the same volume of saline during operation. Unpaired t-test was used to test the significance in normally distributed continuous variable and Mann-Whitney U test was used to test the significance of the difference between the quantitative variables. The software Predictive Analytics Software (PASW) 18.0 was used for statistical analysis and the graphs have been generated using the Microsoft Excel 2007. A p-value of less than 0.05 has been considered to be significant.

Results: There were no significant differences between the two groups with respect to patient characteristics (age, weight, and height).The mean time for two segment regression in the group M was prolonged by around 13 minutes, as compared to group C (104.96±11.37 minutes versus 91.2±11.86 minutes, respectively, p<0.001). The mean regression time up to L2 dermatome in the group M was prolonged by 15 minutes as compared to the group C. (171.23 minutes versus 156.43 minutes, respectively, p=0.0003). The total consumption of tramadol in the group M was significantly lesser than the control group (192.5±58.03 mg and 245.0±43.74 mg, respectively, p=0.0002).

Conclusion: An i.v. infusion of 5 mg/kg MgSO4 prolongs two segment regression time upto L2 dermatome and reduces postoperative opioid consumption without any complication in patients undergoing femur fracture surgery under spinal anaesthesia.