Swathi Gajji and R.Rajeshwar Reddy, “Comparative study of epidural 0.2% ropivacine and fentanyl with 0.2%levobupivacine and fentanyl for postoperative pain relief for modified radical mastectomy”, Int. J. Heal. Clin. Res., vol. 5, no. 2, pp. 1032–1037, Jan. 2022.