Optimum dose of spinal ropivacaine with or without single intravenous bolus of S-ketamine during elective cesarean delivery: a randomized, double-blind, sequential dose-finding study

BACKGROUND: Maternal hypotension after spinal anaesthesia occurs at a high rate during caesarean delivery and can lead to adverse maternal or foetal outcomes. The aim of this study was to determine the optimal dose of spinal ropivacaine for caesarean section with or without intravenous single bolus of S-ketamine and to observe the rates of hypotension associated with both methods. METHODS: Eighty women undergoing elective caesarean delivery were randomly allocated into either a ropivacaine only or ropivacaine with intravenous S-ketamine group. If the upper sensory level of the patient reached T6 and the visual analogue scale (VAS) scores remained below 3 points before delivery, the next patient had a 1/9th chance of receiving a lower dose or an 8/9th chance of receiving the same dose as the previous patient. If the patient had VAS scores of more than 2 points 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 patient VAS score of < 3 points before delivery and the incidence of post-spinal hypotension in both groups. Secondary outcomes included the rates of hypotension-related symptoms and interventions, upper sensory level of anaesthesia, level of sedation, neonatal outcomes, Edinburgh Postnatal Depression Scale scores at admission and discharge, 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. The rates of hypotension and associated symptoms were significantly lower in S-ketamine group than in the ropivacaine only group. CONCLUSIONS: A spinal dose of ropivacaine 12 mg with a single intravenous 0.15 mg/kg bolus dose of S-ketamine may significantly reduce the risk of hypotension and induce sedation before delivery. This method may be used with appropriate caution for women undergoing elective caesarean delivery and at a high risk of hypotension or experiencing extreme nervousness. TRIAL REGISTRATION: http://www.chictr.org.cn (ChiCTR2000040375; 28/11/2020). SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12884-021-04229-y.