Evaluation of magnesium sulfate as an adjuvant to bupivacaine for postoperative analgesia in ultrasound-guided transversus abdominis plane block in patients scheduled for lower segment caesarean section under subarachnoid block – A prospective, randomized, double-blind study

Abstract

Background and Aims: Various adjuvants such as magnesium sulfate (MgSO4), dexamethasone, and clonidine have been used in transversus abdominis plane (TAP) block to prolong the duration analgesia. MgSO4 is N-methyl D-aspartate receptor antagonist (NMDA) and presence of NMDA receptors in skin and muscle can prolong the duration of postoperative analgesia. We aimed to evaluate the effects of MgSO4 as an adjuvant to bupivacaine in ultrasound-guided (USG) TAP block for prolongation of duration of postoperative analgesia. Materials and Methods: Sixty pregnant patients of the American Society of Anesthesiologists physical Status I and II between age group of 18–35 years, scheduled for elective cesarean section under subarachnoid block were allocated randomly into two groups:- Group BM (bupivacaine + MgSO4) and Group B (bupivacaine + Normal saline). All patients received USG bilateral TAP block after caesarean section using either 25 ml of 0.25% bupivacaine and 0.3 ml (75 mg) of 25% injection MgSO4 or 25 ml of 0.25% Bupivacaine and 0.3 ml of normal saline on each side. All patients were evaluated for dynamic pain at 0, 30 min, 1, 2, 4, 6, 12, and 24 h, for postoperative analgesia and adverse effects. The normally and nonnormally distributed data were analyzed using unpaired t-test and Mann–Whitney U-test, respectively. P < 0.05 was considered statistically significant. Results: Duration of analgesia in Group BM (12.3 h. ±0.83666 h) and Group B (12.0333 h. ±1.24522 h) were comparable (P = 0.3348). The average pain scores at different time points did not differ significantly between the two groups (P > 0.05). Conclusion: MgSO4 as an adjuvant to bupivacaine in USG TAP block does not prolong duration of postoperative analgesia.