• Mayank Gupta, Priyanka Gupta, and Dhananjay Kumar Singh.
• Department of Anaesthesia, ICU and Pain Shri Guru Ram Rai Institute of Medical and Health Sciences, Shri Mahant Indiresh Hospital Patel Nagar, Dehradun, Uttarakhand-248001.
• Pain Physician. 2016 Mar 1; 19 (3): E411-20.

BackgroundThe 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.ObjectivesTo 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 DesignProspective, randomized double blind active control trial.SettingMedical college teaching hospital.MethodsNinety 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.StatisticsANOVA, Kruskal Wallis test, Chi-square (x2), and Fisher's exact test, significance: P < 0.05.ResultsThe 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.LimitationsLack of placebo group, exclusion of higher doses (15µg) of ITD, and short duration of postoperative follow-up.ConclusionsThe 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.

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