Comparative evaluation of different doses of intrathecal neostigmine as an adjuvant to bupivacaine for postoperative analgesia

OBJECTIVE: To study the efficacy and safety of intrathecal neostigmine at dose of 50 μg and 150 μg as an adjuvant to bupivacaine for postoperative analgesia under spinal anesthesia. MATERIALS AND METHODS: 75 patients of either sex, belonging to American Society of Anesthesiologists (ASA) physical status I and II in the age group of 30-65 years scheduled to undergo lower abdominal and lower limb surgeries were allocated randomly into 3 groups of 25 each. Spinal anesthesia was administered in Group I (control group) with 12.5 mg (2.5 ml) of 0.5% hyperbaric bupivacaine, in Group II (50 μg group) with 12.5 mg (2.5 ml) of 0.5% hyperbaric bupivacaine and 50 μg (0.1 ml) of neostigmine methylsulphate and in Group III (150 μg group) with 12.5 mg (2.5 ml) of 0.5% hyperbaric bupivacaine and 150 μg (0.3 ml) of neostigmine methylsulphate. Hemodynamic parameters, onset and level of sensory block were recorded. Postoperative analgesic assessment was made in terms of total Visual Analogue Scale-Pain (VAS-P) scores in 24 hrs, duration of analgesia (time to requirement of first analgesic) and total number of rescue analgesic (diclofenac sodium 75 mg intramuscularly) consumption in 24 hours. Side effects were recorded. RESULTS: The total VAS-P score in group I was 23.12 ± 3.21, which was higher than the VAS-P score in group II (18.4 ± 2.92) and group III (16.24 ± 1.85). The total duration of analgesia was significantly prolonged in neostigmine groups (224.40 ± 23.28 min in group I, 367.60 ± 42.15 min in group II and 625.60 ± 87.70 min in group III). In group I, the patients required 2.48 ± 0.51 number of analgesics in 24 hours, which was much higher than required in group II (1.92 ± 0.64) and group III (1.32 ± 0.47). The incidence of nausea and vomiting was more with 150 μg neostigmine group compared to 50 μg neostigmine. CONCLUSIONS: The administration of intrathecal neostigmine in dose of 50 μg as an adjuvant to bupivacaine produces hemodynamically stable analgesia with minimal side effects.