Anatomical shape of the airway.

The shape of the standard endotracheal tube does not conform to the anatomy of the airway and this nonconformity is probably the most injurious factor of tracheal intubation. In order to measure the tube recoil deformation pressure at different points of the airway, it is necessary to know the exact shape of the airway. The contours of the airway were studied from lateral radiographs in patients lying supine on the operating table, with the neck in the normal, extended and flexed position. A computer programme calculated the anterior and posterior contours of the airway as mean values of the original contours on the radiographs as well as of seven selected anatomical points. The mean configuration of the airway in non-intubated individuals was then presented in a standard coordinate system. The "ideal" shape of the airway was subsequently designed in accordance with our results, and this shape can be used clinically as a standard for comparison in cases with suspected pathological configurations.