Comparative dose-response study of hyperbaric ropivacaine for spinal anesthesia for cesarean delivery in singleton versus twin pregnancies

Study objective: It is controversial whether local anesthetic dose requirement for spinal anesthesia for cesarean delivery differs between patients with singleton and patients with multiple gestation pregnancies. The aim of this study was to determine and compare the ED50 and ED90 for hyperbaric ropivacaine used for spinal anesthesia for cesarean delivery in patients with singleton pregnancies versus patients with twin pregnancies. Design: Prospective, randomized, comparative dose-finding study. Setting: Operating room, Women's Hospital, Zhejiang University School of Medicine. Patients: 100 patients with singleton pregnancies (Group S) and 100 patients with twin pregnancies (Group T) presenting for scheduled cesarean delivery under combined spinal-epidural anesthesia were enrolled in the study. Interventions: Patients in Group S or Group T were randomly allocated to receive 9.5, 11, 12.5, 14 or 15.5 mg of hyperbaric ropivacaine intrathecally. A dose was considered effective when it achieved a bilateral sensory block level at the T6 dermatome or above within 10 min after intrathecal injection, there was no numerical rating scale (NRS) pain score >= 3 intraoperatively, and there was no requirement for epidural supplementation at any time during anesthesia and operation. Values for ED50 and ED90 for ropivacaine were determined using probit regression. The difference in ropivacaine dose requirement between patients with singleton pregnancies and patients with twin pregnancies was assessed by calculating relative median potency. Measurements: Success rates for different intrathecal doses of ropivacaine, side effects and neonatal outcomes were recorded. Main results: The estimated (95% confidence interval) values for ED50 and ED90 of intrathecal ropivacaine in patients with singleton pregnancies were 11.2 (10.2 to 12.0) mg and 15.7 (14.4 to 18.3) mg, respectively. The values for ED50 and ED90 in patients with twin pregnancies were 10.5 (9.5 to 11.3) mg and 14.8 mg (13.6 to 17.0) mg, respectively. The estimate of relative median potency for ropivacaine between patients with singleton and twin pregnancies was 0.94 (95% confidence interval 0.83 to 1.04). Conclusion: Patients with singleton and twin pregnancies have similar dose requirement for hyperbaric ropivacaine used for spinal anesthesia for cesarean delivery in the setting of combined spinal-epidural (CSE) anesthesia, no opioids, low weight cohort, insertion with the patients in the right lateral position, and nor epinephrine boluses.