A comparison between epidural Butorphanol and Tramadol for postoperative analgesia, sedation and side effects using CSEA technique for surgeries below the level of umbilicus. International Journal of Biomedical and Advance Research, [S. l.], v. 7, n. 11, p. 537–542, 2016. DOI: 10.7439/ijbar.v7i11.3730. Disponível em: https://ssjournals.co.in/index.php/ijbar/article/view/3730. Acesso em: 11 mar. 2026.