Dose response of perineural magnesium sulphate in ultrasound guided infraclavicular brachial plexus block– A randomized double-blind study

Regional anaesthesia is the choice of anaesthesia for procedures involving the upper limb as it provides effective post-operative pain relief. Brachial plexus block (BPB) has evolved over the years as an important weapon in the armamentarium of anaesthesiologists. Local anaesthetics alone might not provide prolonged pain relief after the surgery because of its limited duration of action. Adding adjuvant to local anaesthetic is one way to prolong the analgesia. Different adjuvants have their own pros and cons. Magnesium sulphate (MgSO4), being a N-methyl-D-aspartate (NMDA) antagonist is an adjuvant to local anaesthetic in central neuraxial block, peripheral nerve blocks and fascial plane blocks. MgSO4 has been known to prolong the duration of analgesia as well as shorten the onset time of block. Different doses of perineural MgSO4 (between 100mg and 250 mg) have been used in clinical practice in brachial plexus block to increase the duration of analgesia. Studies with dose beyond 250 mg have not been used in brachial plexus block. Hence, we planned to compare the doses 125 mg, 250 mg and 500 mg of magnesium sulphate as an additive in infraclavicular brachial plexus block.