Prasad G. V., K.; Sharma, V. J. 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. Int Surg J 2019, 6, 4048-4055.