Comparison of two different doses of magnesium sulphate for spinal anaesthesia.- A prospective, randomized double blind study

Background: The present study aim was designed to compare and evaluate the efficacy of adding two different doses of magnesium sulphate to 0.5% hyperbaric levobupivacaine for spinal anaesthesia in terms of block characteristics, haemodynamic and safety profile. Methods: Ninety American Society of Anaesthesiologist (ASA) grade I?II patients undergoing elective infra-umbilical surgeries under spinal anaesthesia were randomly allocated into three groups. Group C (n=30, control group) received 3 mL (15 mg) of 0.5% hyperbaric levobupivacaine; Group M50 (n=30): received 3 mL (15 mg) of 0.5% hyperbaric levobupivacaine + 50 mg of magnesium sulphate. Group M100 (n=30) received 3 mL (15 mg) of 0.5% hyperbaric levobupivacaine + 100 mg of magnesium sulphate.A standard protocol was followed after which a blinded observer assessed the sensory and motor blocks. The onset and duration of sensory (pin-prick) block, onset, intensity and duration of motor block were recorded. Results: All the subarachnoid blocks were adequate. The addition of magnesium sulphate to intrathecal levobupivacaine had not only increased the time to onset of sensory block (p=0.007) but also prolonged the duration of sensory (p<0.001) and motor block (p<0.001) to statistically significant level in a dose dependent manner. Conclusions: Addition of magnesium sulphate does not offer any further advantage in terms of haemodynamic stability. However, it certainly increases the duration of sensory block to a significant level.