Bagle, A. G.-, W. Thatte, and S. Choudhari. “Preemptive Caudal Anaesthesia in Children With Bupivacaine-Tramadol and Levobupivacaine-Tramadol: A Randomized, Double-Blind, Prospective Study”. Anaesthesia, Pain & Intensive Care, Jan. 2019, pp. 13-19, https://apicareonline.com/index.php/APIC/article/view/321.