Comparison of median effective concentration of spinal ropivacaine in primipara and multipara labor analgesia

Abstract

Background: The existing literature on the median effective concentration (EC50) of local analgesics in primipara during labor is extensive. However, studies focusing on multipara are less prevalent. This study aims to determine and compare the EC50 of spinal ropivacaine without opioids in multiparas and primiparas during labor analgesia. Methods: A total of 30 primiparous and 30 multiparous women were enrolled and divided into two groups. All participants received CSE analgesia for labor, with ropivacaine administered intrathecally without opioids. The concentration of spinal ropivacaine was determined using the up-and-down method, starting with an initial concentration of 0.1% and adjusting in increments of 0.01%. Effective analgesia was defined as a numerical rating scale (NRS) score ≤3 within 10 minutes following spinal administration. The primary outcome was the EC50 (with a 95% confidence interval [CI]) for the two groups. Results: The EC50 for spinal ropivacaine was 0.054% (95% CI, 0.033-0.063%) in primipara and 0.072% (95% CI, 0.044-0.084%) in multipara, there was significant difference between the two groups. Conclusion: The EC50 in the multipara group was significantly higher than that in the primipara group (P < 0.05). Trial registration: This study was registered on the Chinese Clinical Trial Registry (Identifier: ChiCRT2400087716) on August 2, 2024.