@article{h. kocoglu2004patient-controlled,
  title={Postoperative patient-controlled analgesia with intravenous tramadol, intravenous fentanyl, epidural tramadol and epidural ropivacaine+fentanyl combination},
  author={s. aygun,h. kocoglu,s. goksu,m. karaca,u. oner},
  journal={European Journal of Gynaecological Oncology},
  volume={25},
  number={4},
  pages={498--501},
  doi = {10.12892/ejgo200404498},
  year={2004}
}