C.H., M., and L. N. G. “Effects of Fentanyl on Isobaric Ropivacaine in Subarachnoid Anaesthesia for Lower Abdominal and Lower Extremity Surgeries”. International Journal of Research in Medical Sciences, vol. 4, no. 7, Jan. 2017, pp. 2850-5, doi:10.18203/2320-6012.ijrms20161963.