Spinal ropivacaine for cesarean section: A dose-finding study

Background: The dose-response relation for spinal ropivacaine is undetermined, and there are few data available for obstetric patients. Methods: In a prospective, randomized, double-blind investigation, the authors studied 72 patients undergoing elective cesarean delivery. An epidural catheter was placed at the L2-L3 vertebral interspace. Lumbar puncture was then performed at the L3-L4 vertebral interspace, and patients were randomized to receive a dose of spinal ropivacaine diluted to 3 ml with normal saline: 10 mg (n = 12), 15 mg (n = 20), 20 mg (n = 20), or 25 mg (n = 20). Sensory changes assessed by ice and pin prick and motor changes assessed by modified Bromage score were recorded at timed intervals. A dose was considered effective if an upper sensory level to pin prick of T7 or above was achieved and epidural supplementation was not required intraoperatively. Results: Anesthesia was successful in 8.3, 45, 70, and 90% of the 10-, 15-, 20-, and 25-mg groups, respectively. A sigmoid dose-response curve and a probit log dose-response plot were obtained, and the authors determined the ED50(95% confidence interval) to be 16.7 (14.1-18.8) mg and the ED95(95% confidence interval) to be 26.8 (23.6-34.1) mg. Duration of sensory and motor block and degree of motor block, but not onset of anesthesia, were positively related to dose. Conclusions: The ED50and estimated ED95for spinal ropivacaine were 16.7 and 26.8 mg, respectively. Ropivacaine is a suitable agent for spinal anesthesia for cesarean delivery.