Fig. 3. Arterial partial pressure of oxygen (Pao2) at different levels of inspiratory oxygen concentration. The Pao2was measured by serial arterial blood gas analyses at baseline, after 3 and 5 min of preoxygenation, and after 1, 2, and 3 min of apnea. Three levels of fraction of inspired oxygen (Fio2) were compared (21, 50, and 100%—cumulative) as well as fluid resuscitation (□) versus no fluid resuscitation (•). preox = preoxygenation with Fio221, 50, or 100% after 3 and 5 min.