Comparison of Different Doses of Dexmedetomidine as Adjuvant for Infraumbilical Surgery in Patients Receiving Bupivacaine Spinal Anesthesia: A Randomized Controlled Trial.

Background: Infraumbilical surgery today is done preferentially under subarachnoid block. The relatively short duration of analgesia is a limiting factor which is overcome by adding an adjuvant to intrathecal bupivacaine. We aimed to determine optimum dose of intrathecal dexmedetomidine as adjuvant to 0.5% hyperbaric bupivacaine in infraumbilical surgery.

Methods: A parallel group, double blind, randomized controlled trial was done with 105 adult patients posted for infraumbilical surgery under subarachnoid block. All subjects received 3.0 mL (15.0 mg) of 0.5% hyperbaric bupivacaine. Groups D5.0, D7.5, and D10.0 (n = 35 each) received additionally 5.0, 7.5, and 10.0 mcg intrathecal dexmedetomidine as adjuvant. The onset time of sensory block, its peak level and time to this level, maximum motor block and time to it, total duration of analgesia (time to first rescue), and vital parameters were recorded at intervals. Postoperative analgesia was assessed by visual analog scale score at 15 and 30 minutes, then every 30 minutes until 2 hours and then every hour until 6 hours. Treatment emergent adverse events (bradycardia, hypotension, and sedation) were documented.

Results: Maximum sensory level achieved was higher in Group D10.0 than in the other two groups. There was significant and dose-dependent shortening of the mean time to peak sensory block (3.9, 3.3, and 2.9 min; P ＜ 0.001) and peak motor block (5.6, 5.3, and 4.8 min; P ＜ 0.001), and prolongation of postoperative analgesia duration (206.9, 220.8, and 244.0 min; P ＜ 0.001) with escalating doses (5.0, 7.5, and 10.0 mcg, respectively) of dexmedetomidine. Hemodynamic effects and adverse events were comparable in the three groups.

Conclusions: Intrathecal dexmedetomidine (10.0 mcg), as adjuvant to 0.5% hyperbaric bupivacaine (15.0 mg), facilitates rapid onset sensory and motor block and prolongs duration of postoperative analgesia in spinal anesthesia without significant adverse effects. Although absolute differences are modest, the results are better compared to 5.0 and 7.5 mcg doses.