A Comparison Between Epidural Butorphanol and Tramadol for Postoperative Analgesia, Sedation and Side Effects Using CSEA Technique for Surgeries below the Level of Umbilicus. Int J of Biomed & Adv Res 2016, 7 (11), 537-542. https://doi.org/10.7439/ijbar.v7i11.3730.