Ni, X., X. Zhao, M. Li, Q. Li, and Z. Liu. “Thoracic Epidural Anesthesia for Gas-Free Trans-Umbilical Single Port Laparoscopic Cholecystectomy: A Case Report”. International Surgery Journal, vol. 4, no. 1, Dec. 2016, pp. 420-2, doi:10.18203/2349-2902.isj20164483.