Efficacy of spinal additives neostigmine and magnesium sulfate on characteristics of subarachnoid block, hemodynamic stability and postoperative pain relief: A randomized clinical trial.

Background: Intrathecal neostigmine and magnesium sulfate (MgSO4) produce substantial antinociception, potentiate analgesia of bupivacaine without neurotoxicity.
Aims: The aim was to investigate the effect of neostigmine and MgSO4 on characteristics of spinal anesthesia (SA), hemodynamic stability and postoperative analgesia when added to 0.5% hyperbaric bupivacaine for SA.
Subjects and Methods: In this prospective, randomized, double-blind study 75 American Society of Anesthesiologist status I and II adult females posted for major gynecological surgery were assigned to one of the three groups (n = 25). Group N received Neostigmine 25 μg, Group M received MgSO4 50 mg, Group C received 0.5 ml saline as an adjuvant to 17.5 mg hyperbaric bupivacaine. Onset, duration of block, heart rate, mean arterial pressure, postoperative analgesia, analgesic requirement, and adverse effects were recorded. Data expressed as mean (standard deviation) or number (%). P <0.05 were statistically significant.
Results: The three groups were comparable in characteristics of SA. The mean duration of analgesia was significantly longer in Group N (5.1 h) followed by Group M (4.2 h) and Group C (3.8 h) (P = 0.0134). Analgesic requirement was significantly less in Group N followed by Group M and Group C (P = 0.00232). The pain score was significantly less in Group M (P < 0.05). The incidence of hypotension and vasopressor requirement was lowest (48%) in Group N than in Group M (64%) and Group C 84% (P = 0.0276). The incidence of bradycardia and atropine requirement was the lowest in Group M (P = 0.0354). Sedation was observed in 56% patients in Group M compared to 20% in Group N and 8% in Group C (P = 0.0004).
Conclusion: Intrathecal Neostigmine and MgSo4 does not affect characteristics of SA. Postoperative analgesia of neostigmine was better than MgSO4. Neostigmine provides some protection against hypotension of SA whereas MgSO4 protects against bradycardia.