Effect of 3 Different Doses of Intrathecal Dexmedetomidine (2.5µg, 5µg, and 10 µg) on Subarachnoid Block Characteristics: A Prospective Randomized Double Blind Dose-Response Trial.

BACKGROUND The extended analgesic efficacy of intrathecal dexmedetomidine (ITD) has been investigated in a few clinical trials; however, there is a lack of conclusive evidence upon its ideal dosage. OBJECTIVES To elucidate the dose-response relationship between ITD and subarachnoid block characteristics, particularly the duration of analgesia and differential analgesia (DA: defined as time difference from the offset of motor blockade to the first analgesic requirement on numerical rating scale = 4.0). STUDY DESIGN Prospective, randomized double blind active control trial. SETTING Medical college teaching hospital. METHODS Ninety adult (18 - 60 years) patients undergoing elective lower abdominal and lower limb surgeries were randomized into 3 groups to receive intrathecal 0.5% bupivacaine 3 mL with 2.5 µg (group BD2.5), 5µg (group BD5), or 10 µg (group BD10) dexmedetomidine in 0.5 mL normal saline. The 2 segment sensory regression times (TSSRT), duration of motor blockade analgesia, DA, and perioperative adverse effects were assessed. The primary outcome was duration of analgesia and DA. STATISTICS ANOVA, Kruskal Wallis test, Chi-square (x2), and Fisher's exact test, significance: P < 0.05. RESULTS The onset of sensory block was significantly earlier in group BD10 compared with group BD5 (P = 0.035) and BD2.5 (P = 0.010) while the onset of motor block was significantly earlier in group BD10 compared with BD2.5 (P = 0.020). There was a significant and dose-dependent prolongation of the duration of sensory block (127.50, 149.17, and 187.50 minutes; P < 0.001), motor block (258.50, 331, and 365 minutes; P < 0.001), analgesia (306.17, 396.50, and 512 minutes; P < 0.001), and DA (47.67, 65.50, and147 minutes; P < 0.001) with escalating doses of ITD, respectively. Group BD10 required significantly fewer rescue analgesics compared with other 2 groups (P = 0.001). Except for mild sedation which was significantly higher in group BD10; all the groups were comparable with respect to hemodynamic and other adverse effects. LIMITATIONS Lack of placebo group, exclusion of higher doses (15µg) of ITD, and short duration of postoperative follow-up. CONCLUSIONS The addition of 10 µg compared with 2.5 µg or 5µg ITD to 0.5% hyperbaric bupivacaine is associated with significantly earlier onset of sensory and motor block as well as prolonged duration of sensory block, motor block, analgesia, and DA with a comparable adverse effect profile.