Application of programmed intermittent epidural bolus mode in labor analgesia and its effect on umbilical cord blood flow and blood gas in umbilical arteryPAN Xuelin¹,LIU Qing²,ZHANG Ying²,TANG Yong¹(1.Department of Anesthesiology， Sichuan Jinxin Women and Children’s Hospital，Chengdu 610011，China；2.Department of Anesthesiology， Affiliated Hospital of Traditional Chinese Medicine， Southwestern Medical University，Luzhou 646000，China）