Bhargava, S., A. Tamaskar, N. Chakravarty, S. Shende, and R. V. Shidhaye. “Comparative Study of Thoracic Epidural Fentanyl With Sufentanil for Postoperative Pain Relief in Thoracic Surgery”. Anaesthesia, Pain & Intensive Care, Jan. 2019, pp. 260-4, https://mail.apicareonline.com/index.php/APIC/article/view/436.