Optimum Dose of Spinal Ropivacaine with or Without Single Intravenous Bolus of S-Ketamine During Elective Cesarean Delivery: A Randomized, Sequential Dose-Finding Study

Background Post-spinal hypotension has a high occurrence during cesarean delivery, and can lead to adverse maternal or fetal outcomes. The purpose of the study was to determine the optimal dose of spinal ropivacaine for cesarean section with or without intravenous single bolus of S-ketamine and to observe the incidences of hypotension of both methods. Methods Eighty women undergoing elective cesarean delivery were randomly allocated into Group ropivacaine or Group ropivacaine with intravenous S-ketamine. If the upper sensory level of the patient reached T6 and the visual analogue scale (VAS) scores continuously below 3 before delivery, the next patient had a 1/9th chance of receiving a lower dose or an 8/9th chance of receiving the same of previous dose. If the patient had VAS scores above 2 or needed an extra epidural rescue bolus before delivery, a higher dose was used for the next patient. The primary outcome was the successful use of spinal ropivacaine to maintain VAS of patients below 3 before delivery and the incidence of post-spinal hypotension of both groups. Secondary outcomes included the incidences of hypotension related symptoms and managements, upper sensory level of anesthesia, level of sedation, neonatal outcomes, Edinburgh postnatal depression scale scores on admission and discharging of hospital and post-operative analgesic effect. The 90% effective dose (ED90) and 95% confidence interval (95% CI) were estimated by isotonic regression. Results The estimated ED90 of ropivacaine was 11.8 mg (95% CI 11.7–12.7) with and 14.7 mg (95% CI 14.6–16.0) without intravenous S-ketamine using biased coin up-down sequential dose-finding method, and the incidences of hypotension and its related symptoms were significantly lower in S-ketamine group. Conclusions A spinal dose of ropivacaine 12 mg with single intravenous 0.15 mg/kg bolus dose of S-ketamine may significantly reduce the risk of hypotension and provide sedative status before delivery, thus the method could be cautiously used in parturients with high risks of hypotension or extreme nervousness. Clinical trial registration: http://www.chictr.org.cn (ChiCTR2000040375; 28 Nov 2020)