Magnesium Sulphate versus Neostigmine as an Additive to Bupivacaine In Spinal Anesthesia

Background: Spinal magnesium has been found to prolong the duration of analgesia in various surgical procedures. Spinally administered neostigmine causes analgesia in animals and humans by preventing the breakdown of synaptically released acetylcholine, The present study was designed to compare the analgesic efficacy and side effects of either intrathecal magnesium sulfate or neostigmine added to bupivacaine in patients receiving spinal anesthesia.. Methods: 60 patients were randomised into three groups with 20 patients. Group "I" received 3 mL (15 mg) of hyperbaric bupivacaine + 0.1 mL normal saline , Group "II" received 3 mL (15 mg) of hyperbaric bupivacaine + 0.1 mL (50 mg) of magnesium sulfate . Group''III" received 3 mL (15 mg) of hyperbaric bupivacaine + 0.1 mL (50 mcg) of neostigmine . Onset of sensory and motor block, peak sensory level, time to peak sensory level, time to best motor block, intraoperative hemodynamics side effects ,duration of analgesia, recovery of motor block ,visual analogue score, time to first analgesic request and postoperative side effects were noted. Results: Patients charcteristics and duration of surgery were comparable (P>0.5). Time of onset of sensory and motor blockade was significantly delayed in Group II compared with Group I and III. It was significantly shorter in GroupIII compared to Group I. The .highest sensory level showed non significant difference in the three groups. A statistically significant longer duration of analgesia was observed in GroupII and III compared with the control GroupI while in group III, it was significantly longer compared to group II. Also the recovery of both sensory and motor blockade was found to be statistically significantly longer in group II and III compared to Group I while group III showed significantly longer time compared to Group II. The hemodynamic parameters were comparable in the perioperative period in the three groups (P>0.05). The incidence of side-effects in the three groups were also comparable (P>0.05). Conclusion: The addition of 50 mg intrathecal magnesium or 50mcg neostigmine succeeded significantly and safely in prolonging duration of analgesia without increasing the incidence of side-effects. Also, there was a significant delay in the onset of both sensory and motor blockade in the magnesium group compared to the neostigmine group..