Intrathecal dexmedetomidine as an adjuvant to plain ropivacaine for spinal anesthesia during cesarean section: a prospective, double-blinded, randomized trial for ED(50) determination using an up-down sequential allocation method

BACKGROUND: Intrathecal dexmedetomidine, as an adjuvant to local anesthetics, has been reported to improve the quality of spinal anesthesia and reduce the required local anesthetic dose. However, the optimal dosage regimen for intrathecal dexmedetomidine combined with plain ropivacaine for cesarean section (CS) remains undetermined. The present study aimed to determine the median effective dose (ED(50)) of intrathecal dexmedetomidine as an adjuvant to plain ropivacaine for spinal anesthesia during CS. METHODS: Sixty parturients undergoing CS were randomly assigned to either group: plain ropivacaine 8 mg (Group Rop(8)) or plain ropivacaine 10 mg (Group Rop(10)). The initial dosage of intrathecal dexmedetomidine in each group was 5 µg. The effective dose was defined as a bilateral sensory block at the level of T6 or above to pinprick attained within 10 min after intrathecal injection, without the need for supplementary intraoperative epidural anesthesia. Effective or ineffective responses were determined, followed by a 1 µg increment or decrement in the dose of intrathecal dexmedetomidine for the next parturient using up-down sequential allocation. ED(50) were calculated using probit regression. RESULTS: The ED(50) of intrathecal dexmedetomidine with plain ropivacaine was 5.9 µg (95% confidence interval [CI], 4.9–7.4 µg) in Group Rop(8) and 3.1 µg (95% CI, 0.1–4.8 µg) in Group Rop(10) (P < 0.05). Hemodynamic stability, side effects, patient satisfaction and neonatal outcomes were comparable between the two groups. CONCLUSIONS: The present data suggested that the ED(50) of intrathecal dexmedetomidine as an adjuvant to 8 mg and 10 mg plain ropivacaine in spinal anesthesia during cesarean section was approximately 6 µg and 3 µg, respectively. TRIAL REGISTRATION: Chinese Clinical Trial Registry, identifier: ChiCTR2200055928. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12871-023-02275-x.