Tanzeela Firdous, Ali Kashif, Sahira Nawaz Khan, Ayesha Waqar, Sufyan Ali, Sumayya Tariq, “Compare the Mean Non Hypoxic Apnea Duration of 20° Head up with Conventional Supine Position during Pre-oxygenation in Patients Undergoing Elective Surgery”, Pakistan Journal of Medical & Health Sciences, vol. 16, no. 07, p. 397, Aug. 2022.