Transdermal nitroglycerin as an adjuvant to intrathecal neostigmine and bupivacaine for prolongation of postoperative pain relief

Objectives: Transdermal nitroglycerin patch is being used as an adjuvant to neostigmine for postoperative analgesia, besides its vasodilator effects on cardiovascular system. We aimed to evaluate the transdermal nitroglycerin for its capability to enhance analgesia when used as an adjuvant to intrathecal neostigmine and bupivacaine in elective lower abdominal surgeries. Methodology: We enrolled 60 adult ASA-1 and 2 patients undergoing lower abdominal surgeries under spinal anesthesia. In this double blind randomized study, patients were assigned into two groups, Group NT received transdermal nitroglycerin patch (5 mg/24 h) and Group NE received placebo patch along with 5 mu g of neostigmine and 15 mg of 0.5% hyperbaric bupivacaine. Spinal anesthesia was performed at L3-L4 level, with 25 gauge spinal needle and 3.5 ml of the drug solution was injected intrathecally per the group allocation. Sensory block was checked using pin prick method and motor block was assessed by modified Bromage scale. Pulse rate, blood pressure and SpO(2) were monitored. Intra-operative complications were noted. Sample size was calculated to be 60 with a total of two groups with alpha of 0.05 and a power of 90 %. Test for analysis among two groups was done by ANOVA for quantitative and Chi-square test for qualitative data. A p < 0.05 was considered as significant. Results: The characteristics of intraoperative block were comparable among two groups. The mean duration of analgesia in Group NT was significantly longer (p < 0.001) than in Group NE (476.9 +/- 17.3 vs. 386.9 +/- 17.2 min respectively). Group NE had higher VAS scores and the number of rescue analgesic requirement was significantly more in Group NE as compared to Group NT. Hemodynamic changes remained insignificant in both groups. Incidence of side effects were not significant in both the groups. Conclusion: We conclude that the transdermal nitroglycerin used as an adjuvant to intrathecal neostigmine and bupivacaine prolongs postoperative analgesia.