D. Mermer, G. Turan, C. Koksal, B. A. Tas, F. Karadogan, and N. Akgun, “Correlation of integrated pulmonary index with clinical observation in unilateral and bilateral spinal anaesthesia in geriatric patients”, Int J Res Med Sci, vol. 4, no. 10, pp. 4438–4443, Dec. 2016.