Comparative dose-response study of intrathecal hyperbaric ropivacaine for cesarean delivery in preterm singleton versus twin pregnancies.

Introduction: Previously, we demonstrated that patients with full-term singletons and preterm twins require similar dose of intrathecal hyperbaric ropivacaine. However, these findings may be attributable to enrolled patients with preterm twin pregnancies. In this study, we aimed to determine the intrathecal dose requirements of hyperbaric ropivacaine for twins and singletons at equal gestational ages.

Methods: We enrolled 75 patients with preterm singletons and 75 patients with preterm twins scheduled for cesarean delivery under combined spinal-epidural anesthesia in this two-arm parallel, randomized, double-blind, dose-response study. Patients with singletons and twins were randomly assigned to receive one of five different doses of hyperbaric ropivacaine: 10, 12, 14, 16, or 18 mg. A probit regression model was used to determine the dose effective in 50% of patients (ED₅₀) and dose effective in 90% of patients (ED₉₀) values. The relative median potency was calculated to compare the ED₅₀ between patients with twins and singletons.

Results: Intrathecal ropivacaine ED₅₀ and ED₉₀ (with 95% CI) in patients with preterm singletons were 9.9 (7.2 to 11.5) mg and 16.8 (14.5 to 22.9) mg, respectively. In patients with preterm twins, these values were 9.2 (95% CI 6.4 to 10.8) mg and 15.6 (95% CI 13.6 to 20.6) mg. Between patients with preterm twins and preterm singletons, the relative potency (ED₅₀ ratios) was 0.933 (95% CI 0.72 to 1.15).

Conclusions: During preterm gestation, intrathecal hyperbaric ropivacaine dose requirements for scheduled cesarean delivery were not different between patients with twins and singletons.

Trial registration number: ChiCTR2100051382.