Real-time ultrasound guidance increases ropivacaine requirement for combined spinal–epidural anesthesia in cesarean delivery compared to landmark technique: a dose-finding study

Whether real-time ultrasound guidance changes the minimum local anesthetic dose (MLAD/ED50) of intrathecal ropivacaine with dexmedetomidine for cesarean delivery under combined spinal–epidural anesthesia (CSEA) remains unclear. We compared MLAD between ultrasound-guided and landmark-guided CSEA. In this randomized trial, 60 parturients undergoing elective cesarean delivery received CSEA at the L3–4 interspace with intrathecal ropivacaine plus dexmedetomidine 5 µg (ultrasound-guided, n = 30; landmark-guided, n = 30). MLAD was estimated using the Dixon up-and-down method (starting dose 10 mg; step size 0.5 mg). Hemodynamics, block characteristics, adverse events, intraoperative VAS scores, and neonatal Apgar scores were assessed as secondary outcomes. Baseline characteristics were similar. MLAD was higher with ultrasound guidance than with landmark guidance (10.14 mg [95% CI 9.87–10.41] vs 9.09 mg [95% CI 8.74–9.45]; p = 0.002), confirmed by probit regression (p = 0.004). Compared to baseline values at T0, both systolic and diastolic blood pressure decreased in both groups; however, the reduction at 5 min after injection was smaller in the ultrasound-guided group than in the landmark-guided group. Sensory/motor block profiles, adverse events, intraoperative VAS scores, and Apgar scores were comparable between groups. When performing ultrasound-guided CSEA at L3–4 for cesarean delivery, clinicians should anticipate a modestly higher intrathecal ropivacaine requirement than with the landmark technique. Both approaches provide comparable anesthesia quality and maternal–neonatal safety; therefore, intrathecal ropivacaine dosing recommendations should be technique-specific. ChiCTR2200058312