A dose-finding randomised controlled trial of magnesium sulphate as an adjuvant in ultrasound-guided supraclavicular brachial plexus block

Background and Aim: Magnesium sulphate (MgSO 4 ) has been used as an adjuvant in brachial plexus block with encouraging results; however, there is no consensus regarding its optimal dose. Thereby, we compared the efficacy of two doses of MgSO 4 as an adjuvant in ultrasound (USG) guided supraclavicular brachial plexus block. Methods: Ninety patients, aged 20–60 years, belonging to American Society of Anesthesiologists physical status 1 or 2, were given USG-guided supraclavicular block. Group B ( n = 30) received 20 ml of 0.5%bupivacaine + 5 ml normal saline (NS), Group BM 0.5 ( n = 30) received 20 ml of 0.5%bupivacaine + 3.75 ml NS and 125 mg MgSO 4 (1.25 ml) and Group BM 1 ( n = 30) received 20 ml of 0.5%bupivacaine + 2.5 ml NS and 250 mg MgSO 4 (2.5 ml). The primary outcome of study was the duration of post-operative analgesia. The normally distributed data were analysed using analysis of variance and categorical data analysed using Chi-square test. Results: Duration of post-operative analgesia was prolonged in Groups BM 1 and BM 0.5 (665.13 ± 97.874, 475.10 ± 53.294) min respectively as compared to Group B (272.03 ± 40.404 min: P = 0.00). The onset times of sensory and motor block were shorter in Group BM 1 (5.17 ± 2.2 min) as compared to Groups BM 0.5 and B (8.9 ± 2.3 and 17.7 ± 5.1 min: P = 0.00) respectively. Sensory and motor block durations were prolonged in Group BM 1 as compared to BM 0.5 and B ( P = 0.00). Conclusions: MgSO 4 as adjuvant in brachial plexus block increases the duration of post-operative analgesia. MgSO 4 in the dose of 250mg has greater efficacy as compared to 125 mg.