A randomized sequential allocation study on the optimum programmed intermittent epidural boluses interval time with different concentrations of ropivacaine combined with the dural puncture epidural technique for labor analgesia - Mao, Jingjing; Chen, Yi; Sun, Linsen; Xu, Xiaoxiao; Xu, Kai; Ren, Tingting; Xiong, Xiangsheng; Zhao, Weibing (Frontiers in Pharmacology, 2025)