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

Background: The extended analgesic efficacy of intrathecal dexmedetomidine (ITD) has beeninvestigated in a few clinical trials; however, there is a lack of conclusive evidence upon its idealdosage.Objectives: To elucidate the dose-response relationship between ITD and subarachnoid blockcharacteristics, particularly the duration of analgesia and differential analgesia (DA: defined as timedifference from the offset of motor blockade to the first analgesic requirement on numerical ratingscale ≥ 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 limbsurgeries 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, andperioperative adverse effects were assessed. The primary outcome was duration of analgesia and DA.Statistics: ANOVA, Kruskal Wallis test, Chi-square (χ2), and Fisher’s exact test, significance: P < 0.05.Results: The onset of sensory block was significantly earlier in group BD10 compared with groupBD5 (P = 0.035) and BD2.5 (P = 0.010) while the onset of motor block was significantly earlier in groupBD10 compared with BD2.5 (P = 0.020). There was a significant and dose-dependent prolongation ofthe 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 BD10required significantly fewer rescue analgesics compared with other 2 groups (P = 0.001). Except formild sedation which was significantly higher in group BD10; all the groups were comparable withrespect to hemodynamic and other adverse effects.Limitations: Lack of placebo group, exclusion of higher doses (15µg) of ITD, and short duration ofpostoperative follow-up.Conclusions: The addition of 10 µg compared with 2.5 µg or 5µg ITD to 0.5% hyperbaric bupivacaineis associated with significantly earlier onset of sensory and motor block as well as prolonged durationof sensory block, motor block, analgesia, and DA with a comparable adverse effect profile.Key words: Analgesia, bupivacaine, dexmedetomidine, differential analgesia, intrathecal, pain,spinal anaesthesia