Figure 71-5 Radiographs of the head and neck of an anesthetized patient show that combining backward head tilt with anterior mandibular displacement results in increased clearance at the tongue base to 22 mm (see Fig. 71-3 ). (From Ruben HM, Elam JO, Ruben AM, et al: Investigation of upper airway problems in resuscitation. Anesthesiology 22:271, 1961.)