I read with interest the report of Johnson et al. ,1assessing the reasons for difficulties in advancing an endotracheal tube over a fiberoptic bronchoscope. They state that their study is the first to provide pictorial evidence of the laryngeal structures that obstruct passage of the endotracheal tube during fiberoptic intubation. I point out that this statement is not correct: I had already shown pictorial evidence of this in 2002, using a method similar to theirs.2 

They stated that the right arytenoid and the interarytenoid soft tissues were the sites of resistance to advancement of the endotracheal tube during awake fiberoptic orotracheal intubation.1This supports my statement in a review article on this topic that the main reasons for difficulty in advancing a tube over a fiberscope is that the tube tends to move posteriorly to the glottis.3Another possible reason for the difficulty, that they did not observe, but I did, was that the endotracheal tube entered the esophageal inlet.2 

There have been reports of esophageal intubation despite correct insertion of a fiberscope into the trachea.3,4I have found that a curved tube was often advanced directly into the esophageal inlet, without impacting on the arytenoid cartilage.2In such a case, resistance was felt, not because the tube was impacting on the arytenoids, but because it was pushing the midsegment of the fiberscope into the esophagus. These findings can explain why rotation of the tube does not always enable the tube into the larynx and why withdrawing the tube for a few centimeters (to remove the tube tip out of the esophagus) before rotating and advancing the tube would often facilitate tracheal intubation. I also have shown that cricoid pressure reduces the difficulty in advancing a tube over a fiberscope, by compressing the esophageal inlet.2 

Johnson et al.  have shown a variable finding that, when a fiberscope is located in contact with the arytenoids, it is more likely to be difficult to advance a tube into the trachea. They also stated that other factors (e.g. , awake vs.  anesthetized) may also have played a role. I suggest that the difference between their and my studies in the incidence of esophageal intubation may be caused by a difference in the head and neck position. Most patients in the study of Johnson et al.  1were neurosurgical cervical spine patients, and optimal positioning of the head and neck were limited, whereas in my study,2the head was placed on a pillow and mildly extended. The esophageal inlet is more likely to be open when the head is extended (imagine that, when one drinks, one would place the head and neck to a similar position to this, to open the esophageal inlet). Therefore, the incidence of an endotracheal tube migrating into the esophageal inlet, in theory, is reduced by placing the head and neck into the neutral position.

Fiberoptic intubation is an established useful method in patients with difficult airways. Nevertheless, as Johnson et al.  1pointed out, repetitive attempts at advancing a fiberscope into the trachea and advancing a tube over the scope increase the risk of injury to the larynx and surrounding tissues, leading to bleeding from, or edema of, the tissues. Because the causes of difficulty in tracheal intubation over a fiberscope and the inefficacy of each solution method have not been elucidated fully, we must continue to study to make fiberoptic intubation safer.

Kansai Medical University, Moriguchi City, Osaka, Japan. asait@takii.kmu.ac.jp

Johnson DM, From AM, Smith RB, From RP, Maktabi MA: Endoscopic study of mechanisms of failure of endotracheal tube advancement into the trachea during awake fiberoptic orotracheal intubation. Anesthesiology 2005; 102:910–4
Asai T, Murao K, Johmura S, Shingu K: Effect of cricoid pressure on the ease of fibrescope-aided tracheal intubation. Anaesthesia 2002; 57:909–13
Asai T, Shingu K: Difficulty in advancing a tracheal tube over a fibreoptic bronchoscope: Incidence, causes and solutions. Br J Anaesth 2004; 92:870–81
Koga K, Asai T, Latto IP, Vaughan RS: Effect of the size of a tracheal tube and the efficacy of the use of the laryngeal mask for fibrescope-aided tracheal intubation. Anaesthesia 1997; 52:131–5