To the Editor:—
A Cormach and Lehane 1grade III view of the glottus often is associated with difficulty in passing an endotracheal tube. This situation occurs infrequently; I estimate that I have encountered no more than 200 such patients during 30 yr of practice. In this letter, I describe a modification of a conventional intubation technique using a laryngotracheal spray cannula to identify the laryngeal aperture and guide the endotracheal tube into the trachea.
The LTA 360 Kit (Abbott Laboratories, North Chicago, IL) is a disposable syringe and cannula unit. The unit consists of a semi-flexible, curved white cannula, 3 mm in diameter and 20 cm in length, fused to a 4-ml syringe filled with 4 ml lidocaine HCl, 4%. A black mark 10.5 cm proximal to the rounded distal tip provides a visual aid for the depth of insertion. With the black mark at the glottis, the multiple perforations in the cannula lie beneath the vocal cord and spray the trachea with topical anesthetic.
I use the LTA kit before intubating all my adult patients. If during laryngoscopy I do not see the familiar anatomical landmarks of the larynx, I try one or more of the conventional maneuvers, such as changing the position of the head, changing laryngoscope blade, or asking an assistant to apply pressure to the thyroid and cricoid cartilages. If these maneuvers fail, I plan for an alternative technique to intubate the trachea. However, if I can see the epiglottis and the posterior margin of the larynx (Cormack and Lehane 1grade III), I will proceed with the intubation using the following technique.
With the laryngoscope in one hand and the LTA cannula in the other, I use the distal tip of the cannula to probe and identify the larynx. As I attempt to pass the cannula under the epiglottis and between the vocal cords, I try to displace the arytenoids posteriorly and to get a glimpse of the posterior commissure. I spray the larynx and trachea with the LTA lidocaine and then, while neither removing the laryngoscope from the hypopharynx nor removing the LTA cannula from between the vocal cords, I continue with the intubation sequence. With the LTA cannula resting against the right corner of the mouth, I insert the endotracheal tube between the LTA cannula (on the right) and the laryngoscope (on the left) and advance the endotracheal tube in the same direction as the cannula. When the endotracheal tube is presumed to be in the trachea, I remove the LTA cannula from the mouth, attach the tracheal tube to the anesthesia breathing circuit, and check for tracheal intubation by exhaled carbon dioxide and breath sounds.
I also have used this technique for two additional groups of patients (Cormach and Lehane 1grade II) who may present a challenge to intubate. One group includes patients with a short epiglottis, an epiglottis that does not adequately retract with a curved laryngoscope and continually slips off the tip of a straight blade. The second group of patients includes the morbidly obese, particularly those with obstructive sleep apnea, whose pharyngeal soft tissues impinge on a clear view of the distinct landmarks of the larynx.
Other related techniques have been described. Nolan and Wilson 2evaluated the use of a gum elastic bougie for tracheal intubation in a similar patients (Cormach and Lehane 1grades II and III). They first placed an elastic guide into the trachea and then threaded the endotracheal tube over the guide. I have not had an opportunity to compare their technique with mine. However, in my practice, the LTA cannula is more readily available then the gum elastic bougie.
My personal series using this LTA cannula technique for 3 yr includes approximately 30 patients. For these patients, this technique has been 100% successful. I offer three possible explanations for the success of this technique. (1) The thin LTA cannula is easier to view as it passes into the glottis than is the thicker endotracheal tube. (2) The LTA cannula improves the exposure of the glottis by displacing the arytenoid cartilage posterior and lifting the epiglottis. (3) By using the movement of the LTA cannula to instruct an assistant applying posterior pressure to the larynx, I optimize the position and exposure of glottis.
I must emphasize that when one decides to use this technique and to leave the LTA cannula in the trachea, one is committed to continuing the intubation sequence. If the patient requires ventilation by mask, the LTA cannula must be removed. Initially, this technique may feel awkward, but hopefully, this communication will encourage other anesthesiologists to try it. For anesthesiologists who already use the LTA cannula as part of their routine intubation technique, this technique may facilitate a difficult intubation and obviate the need for additional equipment and the risk of additional attempts at tracheal intubation.