ED50 and ED95 of Spinal Isobaric Ropivacaine in Patients Undergoing Cesarean Delivery

Objective To evaluate the effect of isobaric ropivacaine used in spinal anesthesia on cesarean section. Methods A total of 180 cases scheduled for cesarean section from August 2012 to April 2013 in Guangzhou Women and Children Medical Center were randomly divided into 9 groups and each group had 20 cases. Each group were given isobaric ropivacaine 7 mg (group R7),8 mg(group R8),9 mg(group R9),10 mg(group R10),11 mg(group R11),12 mg(group R12),13 mg(group R13),14 mg(group R14), and 15 mg(group R15),respectively. Every subject was punctured in L3~L4 intervertebral space,then isobaric ropivacaine was injected into the subarachnoid space. The time to T6 sensory block onset, anesthetic effect, Apgar scores, and adverse events were recorded. A dose was considered effective if an upper sensory level to pin prick of T6 or above was achieved and epidural supplementation was not required intraoperatively. The doses of isobaric ropivacaine for effective analgesia in 50 % and 95 % of patients(ED50 and ED95) and 95 % confidence interval(CI) were calculated by Probit method. General data among 9 groups had no significant difference(P>0. 05). The study protocol was approved by the Ethical Review Board of Investigation in Human Beings of Guangzhou Women and Children Medical Center. Informed consent was obtained from each participating patient. Results With the dose increased, the time to T6 sensory block onset shortened gradually. The incidence rates of hypotension in group R14 and group R15 were higher than those in other groups(P<O. 05). The ED50 and ED95 (95%CI) of isobaric ropivacaine was 8. 0 mg[(6. 9~ 8. 7) mg] and 12. 7 mg [(11. 8~14. 5) mg],respectively. Conclusions The ED50 and ED95 of ropivacaine used in spinal anesthesia for cesarean section were 8. 0 mg and 12. 7 mg. With the dose increased,the incidence rate of hypotension increased gradually. Key words: cesarean section; ropivacaine; hypotension; anesthesia, spinal