Gupta, A.; Tiwari, T.; Kapoor, R.; Malik, A.; Abbas, H.; Singh, P. R. Comparative Study of Ropivacaine With Ropivacaine-Fentanyl and Ropivacaine-Fentanyl- Magnesium Sulfate in Epidural Anesthesia for Lower Limb Surgeries. Int Surg J 2018, 5, 1300-1305.