Thati Ajith Kumar, P.Sreedevi, Anjali Rajan, and Pramod Parthasarathy. “A Study of Safety and Efficacy of Analgesia and Anaesthesia Between Intrathecal Fentanyl and Butorphanol As Adjuvants With Bupivacaine 0.5% Heavy for Lower Limb Orthopedic Surgeries”. International Journal of Health and Clinical Research, vol. 4, no. 20, Nov. 2021, pp. 45-51, https://ijhcr.com/index.php/ijhcr/article/view/3175.