Shafa, Amir, et al. “Comparison of Pre-Emptive Analgesic Effect of Rectal Ketamine and Caudal Bupivacaine in Pediatric Lower Abdominal Surgery”. Iranian Journal of Pediatric Surgery, vol. 4, no. 2, Dec. 2018, pp. 61-70, doi:10.22037/irjps.v4i2.22280.