Determination of the ED50 and ED95 of intrathecal ropivacaine for labor analgesia in multiparous women

With the implementation of China’s two-child policy,the number of multiparous women has increased significantly. However, most studies on labor analgesia have focused on nulliparous women, and research on analgesia for multiparous women remains relatively limited. This study aimed to determine the median effective dose (ED 50 ) and 95% effective dose (ED 95 ) of intrathecal ropivacaine for labor analgesia in multiparous women. Thirty multiparous parturients were enrolled. The initial dose of intrathecal ropivacaine was set at 3.0 mg. For each subsequent participant, the dose was adjusted by 0.3 mg increments or decrements based on the analgesic response of the previous subject. Effective analgesia was defined as a numerical rating scale (NRS) score ≤ 3 achieved within 10 minutes after intrathecal administration. If analgesia was effective, the ropivacaine dose for the subsequent patient in that group was decreased by 0.3 mg. Conversely, if analgesia was ineffective, the dose for the next patient in that group was increased by 0.3mg. For women with ineffective analgesia 10 minutes after intrathecal study drug administration,10 mL of 0.08% ropivacaine combined with 0.4 μg/mL sufentanil was administered epidurally as rescue analgesia. The ED 50 and ED 95 of intrathecal ropivacaine determined by Probit regression were 2.16 mg (95% CI: 1.83–2.39 mg) and 2.76 mg (95% CI: 2.49–3.02 mg), respectively. The incidence of adverse events during effective spinal analgesia was low. No cases of bradycardia, respiratory depression, hypotension, or motor block were observed. The ED 50 and ED 95 of intrathecal ropivacaine for labor analgesia in multiparous women during spontaneous latent phase labor were 2.16 mg and 2.76 mg, respectively. (www.chictr.org.cn, registration number: ChiCTR2100054379).