G. Doğanay, P. Ekmekçi, B. K. Kazbek, H. Yılmaz, G. Erkan, and F. Tüzüner, “Effects of alfentanil or fentanyl added to propofol for sedation in colonoscopy on cognitive functions: Randomized controlled trial”, Turkish Journal of Gastroenterology, vol. 28, no. 6, pp. 453–459, Jan. 2017.