Prasad G. V., K., and V. J. Sharma. “A Comparative Study of Hemodynamic Changes and Adverse Effects of Intrathecal Bupivacaine With Fentanyl and Intrathecal Bupivacaine With Clonidine in Infra-Umbilical Abdominal and Lower Limb Surgery”. International Surgery Journal, vol. 6, no. 11, Oct. 2019, pp. 4048-55, doi:10.18203/2349-2902.isj20195121.