Fig. 4. Posterior atlantodental interval (PADI) in millimeters measured preoperatively and during general anesthesia. Mask position: during airway management. Intubation position: during orotracheal intubation. Flat pillow position: after orotracheal intubation with the head positioned on a flat pillow. Protrusion position: after orotracheal intubation with the head positioned on a donut-shaped pillow on top of the flat pillow. * P < 0.05.