Effect of i.v. Magnesium Sulphate versus i.v. Dexamethasone on Intraoperative Haemodynamic and Postoperative Analgesia after Spinal Anaesthesia in Lower Limb Surgeries: A Randomised Clinical Study

Abstract

Introduction: Intrathecal adjuvants have gained favour in recent years with the goal of extending the duration of a block. Among these, Dexamethasone possesses anti-inflammatory and analgesic action and can be given as an adjuvant to local anaesthetics to enhance the efficacy of regional anaesthesia, as well as to decrease the intensity of shivering. The addition of Magnesium sulphate (MgSO4) to spinal anaesthesia helps in improving postoperative analgesia in an orthopaedic setting. Aim: To compare the effects of Intravenously (i.v.) MgSO4 and i.v. dexamethasone on intraoperative haemodynamics, the time to achieve dermatome T10 intraoperatively, and to compare postoperative Visual Analogue Scale (VAS) scores between the two groups at 1, 3, 6, 12, and 24 hours after surgery. Materials and Methods: This randomised clinical trial was conducted, and patients were randomly divided into two groups. Group M (n=40): MgSO4 40 mg/kg given 15 minutes before spinal anaesthesia in 100 mL normal saline infusion i.v. Group D (n=40): Dexamethasone 8 mg given 15 minutes before spinal anaesthesia in 100 mL normal saline infusion i.v. The parameters assessed included haemodynamic parameters, time to achieve dermatome T10 intraoperatively, postoperative VAS score at 1, 3, 6, 12, and 24 hours after surgery, and any side-effects like sedation, respiratory depression, nausea, vomiting, pruritus, urinary retention, bradycardia, and hypotension. Statistical testing was conducted using the statistical software Statistical Package for Social Sciences (SPSS) 28.0. Results: There was no significant difference in demographic variables (age and gender) between the two groups (p-value>0.05). However, the decrease in mean heart rate, Systolic Blood Pressure (SBP), Diastolic Blood Pressure (DBP), and Mean Arterial Blood Pressure (MAP) was greater in group D compared to group M at different time intervals (p-value<0.05). Additionally, dermatome level T10 was achieved earlier in group D by approximately two minutes compared to group M (6.95±0.39 minutes versus 5.03±0.16 minutes, respectively, p-value<0.001). Conclusion: An i.v. infusion of 8 mg dexamethasone in 100 mL normal saline was more effective compared to an i.v. infusion of 40 mg/kg MgSO4 in terms of achieving more stable haemodynamics intraoperatively and achieving the T10 dermatome level earlier.

Keywords

• analgesics
• bupivacaine
• injections
• postoperative pain
• subarachnoid block