Effect of Addition of Magnesium Sulphate to Fentanyl and Hyperbaric Bupivacaine in Spinal Anaesthesia for Abdominal Hysterectomy: A Randomised Clinical Study

Introduction: Subarachnoid block is the most acceptable and popular mode of anaesthesia for gynaecological surgeries. Addition of opioids to intrathecal bupivacaine is routinely practised. Magnesium sulphate (MgSo4), when used intrathecally has an advantage in preventing central sensitisation to peripheral nociceptive pain because it is an N-Methyl-D-Aspartate Receptor (NMDA) antagonist.

Aim: To find out the efficacy of MgSO4 as intrathecal additive to combination of fentanyl and hyperbaric bupivacaine in prolonging duration of analgesia.

Materials and Methods: This randomised clinical study was done between June 2022 to November 2022 in women of American Society of Anaesthesiologists (ASA) grade I and II aged 50 to 70 years scheduled for abdominal hysterectomy under spinal anaesthesia. They were randomly divided into two groups of 30 each (group ‘S’ and group ‘M’). Group ‘S’ received spinal anaesthesia with 3 mL (15 mg) of hyperbaric bupivacaine, 0.5 mL (25 μg) of Fentanyl and 0.1 mL of 0.9% normal saline while group ‘M’ received 3 mL of hyperbaric bupivacaine, 0.5 mL (25 μg) of Fentanyl and 0.1 mL (50 mg) of 50% MgSO4 intrathecally. End points of observation were time for onset of sensory and motor block and duration of analgesia. Data was entered in Microsoft Excel using Statistical Package for Social Sciences (SPSS) version 25.0.

Results: Demographic profile was comparable between both the groups. Delay in onset of sensory block was observed in group ‘M’ (9±0.68 minutes) compared to group ‘S’ (4.88±0.47 minutes) (p<0.001). Similarly, onset of motor blockade too was delayed in group ‘M’ (11.92±0.71 minutes) compared to group ‘S’ (6.83±0.65 minutes) (p<0.001). Postoperative analgesia was significantly prolonged in group ‘M’ (262±8.3 minutes) compared to group ‘S’ (235±12.3 minutes) with a p-value of <0.001. Haemodynamic profile and side-effects showed no significant difference between both the groups.

Conclusion: Addition of MgSO4 (50 mg) to combination of fentanyl and hyperbaric bupivacaine when given intrathecally prolongs the duration of spinal analgesia significantly in patients undergoing abdominal hysterectomy without significant side-effects.