Efficacy of Magnesium Sulphate versus Dexamethasone with Bupivacaine in Ultrasound-guided Transverse Abdominis Plane Block for Postoperative Pain Relief in Lower Abdominal Surgery: A Randomised Double-blinded Clinical Study

Introduction: Transversus Abdominis Plane (TAP) block is an effective regional anaesthesia technique used to provide analgesia for lower abdominal surgeries. Adjuvants like magnesium sulphate and dexamethasone needs to be explored with regards to prolonged duration and efficacy of analgesia when combined with local anaesthetics such as bupivacaine. Aim: This study aimed to assess the efficacy of 200 mg of magnesium sulphate versus 8 mg of dexamethasone as adjuvants to 0.25% bupivacaine in ultrasound-guided TAP blocks in patients undergoing lower abdominal surgeries under subarachnoid anaesthesia. Materials and Methods: The present randomised, doubleblinded, clinical study was conducted at Department of Anaesthesiology, Dr. DY Patil Medical College, Hospital and Research Centre in Pune, Maharashtra, India, from January 2023 to January 2025, eighty American Society of Anaesthesiologists (ASA) grade I and II patients aged 18-65 years, scheduled for lower abdominal surgeries under spinal anaesthesia were recruited and divided into two groups to receive TAP block postoperatively with either 18 mL of 0.25% bupivacaine with magnesium sulphate 200 mg in 2 mL saline (Group A, n=40), or 18 mL of 0.25% bupivacaine with dexamethasone 8 mg (Group B, n=40). Total duration of analgesia, Visual Analogue Scale (VAS) scores, first rescue analgesic, haemodynamic parameters and any related side-effects were observed in each group post block. The Chi-square test was applied to assess categorical variables, while the student's t-test was utilised for comparisons of continuous variables. A p-value of less than 0.05 was considered to indicate statistical significance. Results: Both groups were comparable in demographic characteristics with mean (SD) age being 27.6±7.78 and 28.8±8.15 years in group A and group B, respectively. Group A had 57.5% female patients and 42.5% male patients, while group B had 65% female patients and 35% male patients. The mean duration of analgesia was significantly longer in group B (501±43.02 mins) compared to group A (399±29.93 mins), (p<0.001). Visual Analog Scale (VAS) scores showed significant differences beginning at 4 hours post block, with group B reporting lower VAS scores than group A at 4, 6, and 8 hours, (p<0.05). Time to first rescue analgesia was also significantly delayed in group B (580±48.58 mins) compared to group A (448±32.50 mins), (p<0.001). Minimal side-effects such as nausea and vomiting were observed in both groups, with no statistically significant difference. Conclusion: The addition of dexamethasone to bupivacaine significantly prolongs analgesia duration, reduces pain scores and delays the need for rescue analgesia without any adverse effects, making it a more suitable adjuvant for TAP blocks in lower abdominal surgeries.