Pokharel, K., T. R. Rahman, S. N. Singh, B. Bhattarai, N. Basnet, and S. Khaniya. “The Efficacy and Safety of Low Dose Epidural Butorphanol on Postoperative Analgesia Following Cesarean Delivery”. Journal of Nepal Medical Association, vol. 47, no. 170, Apr. 2008, doi:10.31729/jnma.310.