The 90% effective dose of intrathecal hyperbaric bupivacaine for Cesarean delivery under combined spinal–epidural anesthesia in parturients with super obesity: an up-down sequential allocation study

Purpose To determine the 90% effective dose (ED 90 ) of intrathecal hyperbaric bupivacaine for Cesarean delivery under combined spinal–epidural anesthesia (CSE) in parturients with super obesity (body mass index [BMI] ≥ 50 kg·m −2 ). Methods We enrolled parturients with BMI ≥ 50 kg·m −2 with term, singleton vertex pregnancies undergoing elective Cesarean delivery under CSE. An independent statistician generated the 0.75% hyperbaric bupivacaine dosing regimen in increments of 0.75 mg using a biased-coin up-down sequential allocation technique. This was combined with 15 μg fentanyl, 150 μg morphine, and normal saline to a volume of 2.05 mL. The initial and maximum doses were 9.75 mg and 12 mg, respectively. Participants, clinical team, and outcome assessors were blinded to the dose. The primary outcome was block success, defined as T6 block to pinprick within ten minutes and no intraoperative analgesic supplementation within 90 min of spinal injection. We determined the ED 90 using logistic regression. Results We enrolled 45 parturients and included 42 in the analysis. All doses achieved a T6 level within ten minutes, and the primary outcome occurred in 0/1 (0%) of the 9.75-mg doses, 2/3 (67%) of the 10.5-mg doses, 21/27 (78%) of the 11.25-mg doses, and 11/11 (100%) of the 12-mg doses. The ED 90 of hyperbaric bupivacaine was 11.56 mg (95% confidence interval, 11.16 to 11.99). Four parturients (9.5%) had sensory level higher than T2, but none was symptomatic or required general anesthesia. Conclusion The estimated ED 90 of hyperbaric bupivacaine with fentanyl and morphine in parturients with super obesity undergoing Cesarean delivery under CSE was approximately 11.5 mg. Study registration ClinicalTrials.gov (NCT03781388); first submitted 18 December 2018.