To the Editor:—
The purpose of passing a nasal RAE tracheal tube (NRT) (Mallinkrodt, St. Louis, MO) over a fiberoptic bronchoscope (FOB) to fiberoptically intubate through a standard Laryngeal Mask Airway ™ (LMA ™) (Laryngeal Mask Co., Henley on Thames, Oxon, UK) (fig. 1) is to gain a 5- to 6-cm greater depth of tracheal intubation compared with a standard endotracheal tube. 1,2A standard endotracheal tube, when fully inserted through an appropriately sized standard LMA ™, enters the trachea by a mere 1–2 cm. 1–3
Figure 1shows a 7.0-mm-ID NRT inside a No. 5 LMA ™ (upper left assembly) and a 6.0-mm-ID NRT inside a No. 4 LMA ™ (lower right assembly). In both assemblies, the distal tip of the NRT is positioned 1 cm proximal to the aperture bars, which then allows one to fiberoptically and sequentially identify the aperture bars, laryngeal structures, and the trachea. The NRT is also positioned within the shaft of the LMA ™ with the Murphy eye at the 12 o’clock position to facilitate passage of the tip of the NRT through the middle compartment of the aperture bars and then the vocal cords (over the FOB). With this spatial arrangement of the NRT inside the LMA ™ and assuming a distance from aperture bar to vocal cord of 4.0 cm, 3fully passing an Olympus BF type P40 FOB (Melville, NY) through a 7.0-mm-ID NRT and passing an Olympus BF type 3C FOB through a 6.0-mm-ID NRT results in the FOB entering the trachea by only 2 and 4 cm, respectively. Indeed, in a few patients (5–10%) with the 7.0-mm-ID NRT, No. 5 LMA ™, and the larger FOB combination, I have been unable to reach the trachea with the FOB by 0.5–1.0 cm; in these instances, the NRT must be advanced at the same time as the FOB is advanced. However, simultaneous NRT and FOB movement significantly complicates the procedure and disturbs the FOB view. The purpose of this letter to the editor is to point out that by simply cutting off the proximal 2 cm of the NRT, one gains a 2-cm greater depth of tracheal entry by the FOB, while maintaining adequate depth of tracheal intubation by the NRT, i.e. , satisfactory clinical performance by both the FOB and the NRT.