Conventional lateral radiography was used in 18 elderly male patients to investigate the changes induced by general anaesthesia in the upper airway. The effect of tongue traction under anaesthesia was studied similarly in another 11 patients. Following induction of anaesthesia, there were highly significant approximations to the posterior pharyngeal wall of the soft palate (median change 1.3 mm, 95% confidence interval (Cl) 0.3-2.6 mm; P = 0.006), tongue base (mean change 6.5 mm, 95% Cl 5.3-7.7 mm; P less than 0.001) and epiglottis (mean change 3.8 mm, 95% Cl 3.1-4.5 mm; P less than 0.001). Apparent radiographic occlusion of the airway occurred most consistently at the level of the soft palate (17 of 18 patients), sometimes at the level of the epiglottis (four patients), but the tongue base did not touch the posterior pharyngeal wall in any patient. Traction on the tongue failed to clear the nasopharyngeal obstruction. Attempted inspiration under anaesthesia caused major secondary collapse of the pharynx, with multiple sites of obstruction, similar to that found in obstructive sleep apnoea.

Soft tissue lateral neck radiography was used in 22 male patients older than 60 yr, to determine the cause of pharyngeal airway obstruction during anaesthesia, before and after insertion of a Guedel airway. In six of the patients, the airway was radiologically and clinically clear with the head in the neutral position. Nine patients showed obstruction of the airway by a "shelf" of tongue, but seven were cleared clinically by dorsiflexion at the atlanto-occipital joint, and the remaining two by the Esmarch-Heiberg manoeuvre. In four of the 22 patients, the Guedel airway was lodged in the vallecula in the neutral position. This was cleared clinically by dorsiflexion at the atlanto-occipital joint in all these patients. In three patients the Guedel airway was obstructed by the epiglottis, but this was cleared by dorsiflexion at the atlanto-occipital joint in two; in the third patient, the Guedel airway slipped into the vallecula after dorsiflexion at the atlanto-occipital joint and remained there despite the Esmarch-Heiberg manoeuvre. There was only one instance in 66 trials of a clinically obstructed airway without an apparent radiological cause. However, there were 10 instances in 66 trials of a clinically clear airway with an apparent radiological cause for obstruction.

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