Abstract: AIM:To determine the median effective dose (ED₅₀)of spinal anesthesia 0.75% ropivacaine for cesarean section.METHODS:Thirty-two ASA Ⅰ-Ⅱ parturients undergoing elective cesarean section delivery with use of combined spinal-epidural anesthesia were enrolled in this study.The initial dose of was 12.8 Mg of 0.75%ropivacaine, and the dosing intervals were 98.4% of the preceding dosage.Doses for subsequent parturients were determined by the response of the previous parturient.Successful anesthesia was defined as a loss of sensation to an acupuncture stimulus at the T₇ level, full motor blockade within 10 minutes after administration of the local anesthetic, analgesia of incision and the satisfaction of skelaxin evaluated by one operator.ED₅₀ and its 95% confidence interval (CI)was determined with use of Dixon method.RESULTS:Five parturients were rejected out the study because of doubtful anesthsia.According to the rest twenty-seven parturients'data, the ED₅₀ of intrathecal 0.75% ropivacaine was 11.97mg (95% confidence interval [CI], 11.75-12.19 mg).CONCLUSION:The ED₅₀ of spinal 0.75% ropivacaine for cesarean delivery under the conditions of this study were 11.97mg.

Key words: cesarean section, combined spinalepidural anesthesia, ropivacaine, median effective dose