Efficacy of magnesium sulfate added to bupivacaine in transversus abdominis plane block for postoperative analgesia after inguinal herniorrhaphy

Abstract

Background Transversus abdominis plane block (TAPB) has proven to be an effective component of multimodal analgesic regimens for a variety of abdominal procedures. Magnesium sulfate (MgSO4) N-methyl-D-aspartate receptor antagonist has the potential to be an ideal adjuvant in TAPB. We studied the efficacy of MgSO4 as an adjuvant to bupivacaine in TAPB in patients scheduled for inguinal hernia repair. Patients and methods A total of 50 adult male patients aged 20–60 years, American Society of Anesthesiologists class I or II, and scheduled for elective primary unilateral open inguinal hernia repair were studied. Patients were randomly allocated into two groups: group 1 (n=25) included 18 ml of 0.25% bupivacaine with 2 ml 0.9% NaCl, and group 2 (n=25) included 18 ml of 0.25% bupivacaine with 2-ml MgSO4 10% (200 mg). They were evaluated for pain at 0, 1, 2, 3, 4, 8, 12, 16, 20, and 24 h. Time to first rescue analgesic and duration of postoperative analgesia were noted. Results Group 2 showed longer duration of postoperative analgesia (P<0.001); lower postoperative visual analog scale scores during rest, where P values at 4, 8, 12, 16, and 20 h postoperatively were less than 0.001, 0.038, 0.037, 0.015, and 0.006, respectively; and lower postoperative visual analog scale scores during movement, where P values at 4, 8, 12, 16, and 20 h postoperatively were less than 0.001, 0.001, 0.001, 0.009, and 0.037, respectively. Group 2 patients had longer time till rescue analgesia, less total dose of opioids, and more patient satisfaction. Conclusions MgSO4 (150 mg) as an adjuvant to bupivacaine in ultrasonographic‑guided TAPB prolongs the duration of analgesia, reduces postoperative pain scores, and decreases demands for rescue analgesics.