The effect of early epidural analgesia on the serum cortisol，endothelin ⁃1 and nitric oxide of parturients 

MA Huanhuan, XU Heng, ZHANG Yonghong, LIU Xiaoou.
The Journal of Practical Medicine . 2021, (10): 1312 -1316 .  DOI: 10.3969/j.issn.1006⁃5725.2021.10.016