Comparative analgesic efficacy of adding magnesium sulphate to bupivacaine in serratus anterior plane block to reduce pain after mastectomy

Abstract

Background: Magnesium sulphate has been used as an adjuvant to anaesthetic mixtures in peripheral nerve blocks. This study aimed to assess the efficacy of magnesium sulphate as an adjuvant to bupivacaine in ultrasound-guided serratus anterior plane (SAP) block for postoperative analgesia in patients undergoing modified radical mastectomy.
Methods: This randomised, double-blinded, controlled trial included adult female patients undergoing modified radical mastectomy under general anaesthesia. The patients were randomised into two groups that underwent ultrasound-guided SAP block. The control group received 28.5 ml of plain bupivacaine 0.5% and 1.5 ml of 0.9% normal saline, while the study group received 28.5 ml of bupivacaine 0.5% and 1.5 ml (750 mg) of magnesium sulphate. All patients were hospitalised postoperatively for at least 24 hours. Both the time to first request for analgesia and the postoperative pain score using the visual analogue scale (VAS) were recorded.
Results: Compared to the control group, the magnesium sulphate group had a significantly longer mean time to first analgesic request (666 vs 462 minutes, p < 0.001), as well as lower VAS at rest (at 4 and 8 hours postoperatively) and VAS at movement (at 2, 4 and 8 hours postoperatively). However, analgesic consumption was comparable between the two groups (p > 0.05). The percentage of satisfied surgeons was significantly higher in the magnesium sulphate group (95% vs 65%, p = 0.018), but patients’ satisfaction did not differ significantly (p = 0.292).
Conclusion: Adding magnesium sulphate during SAP blockade can enhance the analgesic effect and prolong the time to first analgesic request in patients undergoing radical mastectomy.