Comparison of the ED50 of intrathecal hyperbaric ropivacaine co-administered with or without intrathecal dexmedetomidine for cesarean section: A prospective, double-blinded, randomized dose-response trial using up-down sequential allocation method

Study objective: Studies have showed that intrathecal dexmedetomidine as supplements to local anesthetics can improve the quality of the spinal anesthesia and reduce the local anesthetic requirement of spinal anesthesia for cesarean section. However, the magnitude of this effect has not been fully quantified. Therefore, we conducted the present study to investigate the ED50 of intrathecal hyperbaric ropivacaine with or without dexmedetomidine for cesarean section in healthy parturients. ED50 values obtained were compared to estimate the effect of intrathecal dexmedetomidine versus placebo on ropivacaine requirement. Design: Single-blinded, prospective, randomized study. Setting: Department of Anesthesia, Women's Hospital, Zhejiang University School of Medicine. Patients: Sixty healthy parturients under elective cesarean section with combined spinal-epidural anesthesia were randomized into Group C (intrathecal ropivacaine alone) and Group D (intrathecal ropivacaine + 5 mu g dexmedetomidine). Interventions: The dose of intrathecal ropivacaine for the first parturient in both groups was 11 mg. An increment or decrement of 0.5 mg intrathecal ropivacaine was made for the subsequent parturient based on the effective or ineffective response of the previous parturient. Effective dose was defined as a bilateral T6 or above sensory block level was achieved within 15 min after induce of spinal anesthesia and no additional epidural anesthetics was required during surgery. The Dixon and Massay sequential method and Probit regression were applied to calculate the ED50 of intrathecal ropivacaine in both groups. Measurements: Characteristics of spinal anesthesia and side effects were recorded. Main results: The ED50 of hyperbaric ropivacaine calculated by Dixon and Massay formula was 11.4 mg (95% CI, 11.1-11.7 mg) in Group C, and 9.4 mg (95% CI, 9.0-9.7 mg) in Group D (P < 0.05). While using the Probit regression, the ED50 of intrathecal hyperbaric ropivacaine was 11.1 mg (95% CI, 10.7-11.6 mg) in Group C, and 9.1 mg (95% CI, 8.6-9.5 mg) in Group D. Shivering was less observed in Group D than in Group C (P < 0.05). There was no significant difference in the onset time of sensory block or motor block, the incidence of hypotension, bradycardia, nausea and vomiting, sedation and pruritus between the two groups. Conclusion: Under the conditions of the present study, intrathecal dexmedetomidine (5 mu g) reduced the ED50 of intrathecal hyperbaric ropivacaine by approximately 18% for cesarean section in healthy parturients under combined spinal-epidural anesthesia.