Uma Mandal, Indranil Halder, and Keya Chakraborty, “Comparative study of bupivacaine-fentanyl versus bupivacaine-clonidine in patients undergoing spinal anaesthesia for lower abdominal surgery”, Int. J. Heal. Clin. Res., vol. 5, no. 2, pp. 843–849, Jan. 2022.