Kishnani, P., L. K. Jain, K. Patel, and D. Chauhan. “A Study of Intrathecal Fentanyl and Butorphanol As an Adjuvant to 0.5% Bupivacaine [heavy] for Lower Limb Surgeries: Randomized Control Study”. International Journal of Health Sciences, vol. 6, no. S3, Apr. 2022, pp. 1600-8, doi:10.53730/ijhs.v6nS3.5709.