Improvement in postoperative pain relief by the addition of midazolam to an intrathecal injection of buprenorphine and bupivacaine

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Abstract
Background and objective: Intrathecal injections of the benzodiazepine midazolam have been reported to cause antinociception in animals and pain relief in human beings, including the potentiation of opioid analgesia. This study compared the efficacy of the addition of midazolam to a mixture of buprenorphine and bupivacaine used for spinal anaesthesia. Methods: The study was prospective, randomized, and observer blinded. It involved 60 patients (30 per group), ASA I and II, age 20-40 yr, undergoing minor and intermediate lower abdominal surgery under spinal anaesthesia. Patients were randomized into two groups: the control group received a spinal injection of hyperbaric bupivacaine (15 mg) plus buprenorphine (0.15 mg) and the experimental group received a spinal injection of the same two drugs and doses but supplemented with intrathecal midazolam (2 mg). Results: The duration of postoperative analgesia in the control group was 9.24 ± 2.57 h (mean ± SEM), and 21.33 ± 12.69 h in the midazolam treated group (P < 0.001). Patients treated with intrathecal midazolam had better pain relief judged by visual analogue score on coughing (P = 0.0013) and a nursing mobility score (P < 0.0001). Adverse effects were minor and their incidence was similar in both groups. Conclusions: We conclude that intrathecal midazolam 2 mg improves the quality and duration of postoperative pain relief afforded by intrathecal buprenorphine and bupivacaine.