Comparison of the Effects of Adding Dexmedetomidine Versus Midazolam to Intrathecal Bupivacaine on Postoperative Analgesia

Background: Dexmedetomidine and midazolam both modulate spinal analgesia by differentmechanisms, and yet, no human studies are available to compare them for postoperative analgesiaafter neuraxial administration.Objectives: We investigated the addition of dexmedetomidine or midazolam to intrathecalbupivacaine on the duration of effective analgesia and clinical safety profile.Study Design: Prospective, randomized, double blind, placebo controlled study.Setting: University teaching hospital.Methods: The study cohort included a consecutive and prospective series of patients, referredfor endourological procedures. The patients were randomly allocated into 3 groups (20 patientseach) to receive intrathecally 3 mL of 0.5% hyperbaric bupivacaine in combination with 5 mcg ofdexmedetomidine (dexmedetomidine group), 1 mg of midazolam (midazolam group) or 0.5 mL of0.9% saline (control group). The groups were compared to the regression time of sensory block,duration of effective analgesia (defined as the time interval between administration of intrathecaldrug to the time of first analgesic request or a numeric rating scale ≥ 4.0), sedation score, and sideeffects in the first 24 hours.Statistics: One way-ANOVA, Kruskal Wallis test, and Chi-square test (χ2), significance level: P < 0.05.Results: The duration of effective analgesia (time to first analgesic request) was significantlyprolonged in the dexmedetomidine group (286 ± 64 minutes, P < 0.01) when compared withmidazolam group (236.9 ± 64.9 minutes) and the control group (212.7 ± 70.2 minutes). Pairwisecomparisons among the 3 groups with Bonferroni adjustment revealed that patients from thedexmedetomidine group were more sedated in comparison to the midazolam and control groups atthe end of the first 15 minutes after intrathecal injection [χ2 (2) = 7.157, P = 0.028], with a meanrank sedation score of 35.58 for dexmedetomidine, 25.00 for midazolam, and 30.93 for control.No significant differences in the side effects were observed during the study period. Midazolam didnot lengthen the time of the two segment sensory regression or the time to first request analgesia.Limitation: The study cannot be extrapolated to muscle cutting surgeries under spinalanaesthesia.Conclusions: The addition of dexmedetomidine (5 mcg) to 3 mL of intrathecal hyperbaricbupivacaine (0.5%) significantly prolongs the duration of effective analgesia in comparison to1 mg midazolam or placebo (0.9% normal saline) with a comparable incidences of side effects.Key words: Dexmedetomidine, midazolam, intrathecal, spinal anaesthesia, subarachnoid block,postoperative painPain Physician 20