Figure 71-3 Soft tissue roentgenograms of the head and neck of an awake supine patient show that with the head in the neutral position, air clearance at the base of the tongue is about 3 mm. When the patient is unconscious, this small opening is often lost and airway obstruction results. (From Ruben HM, Elam JO, Ruben AM, et al: Investigation of upper airway problems in resuscitation. Anesthesiology 22:271, 1961.)