Colak, Y. Z., U. Ozgul, D. D. Aslan, H. B. Cumurcu, C. Colak, and M. Durmus. “The Effects of Sedation With Propofol and Propofol- Ketamin Combination on Postoperative Cognitive Function in Elderly Patients Undergoing Spinal Anesthesia”. Annals of Medical Research, vol. 28, no. 6, June 2021, pp. 1201-5, http://www.annalsmedres.org/index.php/aomr/article/view/3819.