Effect of two different dosages of adjunct magnesium sulfate on interscalene nerve blockade: A double blind randomized controlled trial

Interscalene nerve block is very commonly performed for clavicle & proximal humerus surgeries. However very few studies have evaluated the effect of add on magnesium sulphate to local anaesthetic for interscalene nerve block. Sixty patients of American Society of Anaesthesiologist (ASA) physical status I and II undergoing surgeries for fracture clavicle and proximal humerus were recruited in this trial. Following randomisation, ultrasound guided interscalene block was performed with 10ml of 2% lignocaine and 20ml of 0.5% bupivacaine either with adjunct 125 mg (MS 125 group, n=30) or 250 mg (MS 250 group, n=30) magnesium sulphate. Primary outcome was to measure and compare the postoperative analgesia, duration of sensory and motor blockade. There was no significant difference between the groups in the duration of sensory blockade [MS 125 v/s MS 250; Mean±SD [Median]; 505.3±44.6 (500) minutes v/s 501.1±45.9(498) minutes; p= 0.65], duration of motor blockade [MS 125 v/s MS 250; Mean±SD [Median]; 314.9±31.1(307) minutes v/s 311.4±34.2(305) minutes; p= 0.7] and the duration of post-operative analgesia [MS 125 v/s MS 250; Mean±SD [Median]; 519±46.1(512) minutes v/s 498±95.8(507 minutes); p=0.43]. Magnesium sulfate at the dose of 125 mg is equally effective as 250 mg for prolonging sensory and motor blockade as well as for post-operative analgesia when used as an adjunct to bupivacaine and lignocaine during interscalene brachial plexus blockade. Our study is limited by small sample size. Further studies with larger sample size are needed.