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. 1, pp. 673–679, Jan. 2022.