To the Editor:—
In the article by Adnet et al. , 1“Randomized Studies Comparing the ‘Sniffing Position’ with Simple Head Extension for Laryngoscopic View in Elective Surgery Patients,” the authors graded two views of each patient's larynx and the degree of difficulty with subsequent intubation. Their results showed no difference in laryngeal exposure between the extended head and sniffing position either at initial laryngoscopy or following repositioning of the head, except in obese patients and those with limited neck mobility. Visualization in these subgroups was best with the head in the sniffing position, but whether this observation was relevant to ease of intubation was not established. Approximately 11% of laryngoscopies were judged to be difficult, while fewer tracheal intubations proved problematic.
One can reasonably reinterpret the authors’ findings and formulate several generalizations that are applicable to all routine intubations. First, resting the head comfortably on a small pillow with the neck flexed and head extended is an acceptable position for laryngoscopy. Moving the head when a difficult laryngoscopy is encountered may sometimes improve visualization but is not likely to enhance the intubating process. Second, a standard technique of intubation, as described in the article by Adnet et al. , is suitable and successful with easy, as well as most, but not all, difficult laryngoscopies. Adnet's experience with intubations also defines the problem for which a solution must be found: a small number of patients required a complex approach to intubation involving participation of an assistant, multiple attempts at passing the endotracheal tube, and possible changes to the method of intubation. Although these patients were exposed to prolonged manipulation, none was harmed under conditions of a controlled trial for elective surgery. However, similar attempts could prove inadequate in other clinical settings, e.g. , emergency surgery for trauma, bowel obstruction, burns, ICU care, and obstetrics where successful first try intubation could be critical to patient outcome. Third, in practice, when a difficult laryngoscopy is encountered, the first view obtained by an experienced operator is probably the best. If the operator proceeds using a standard method of intubation, attempts at introducing the endotracheal tube will be as difficult as the ongoing laryngoscopy. Under this circumstance, the difficult laryngoscopy and difficult intubation appear inseparable, while in actuality, laryngoscopy and tracheal intubation are distinct processes and independent of each other. It is possible to experience a difficult laryngoscopy and yet easily intubate the trachea if the technique of intubation is correct. If an advance is to be made in improving intubation of patients with difficult laryngoscopies, it will not be found in attempts at bettering laryngeal view since near-maximal exposure has been attained with presently used equipment and techniques of laryngoscopy. The answer is to routinely use a technique of intubation that works equally well for both easy and difficult airways.
During difficult intubation, any technique must overcome physical obstacles within the upper airway that hinder movement of the endotracheal tube toward the glottis. Several considerations include:
Current techniques of laryngoscopy create a passage within the upper airway of unique size and shape for a given individual, which is not easily altered by manipulation carried out during laryngoscopy. The anesthesiologist is forced to use the passage through the upper airway as it exists at the time of initial laryngoscopy.
To reach the vocal cords, the endotracheal tube must travel through the laryngoscopic channel created by a curved laryngoscope blade without touching any part of the airway; otherwise, it will be deflected away from the glottic opening.
The endotracheal tube must have a correct shape and must be delivered in a proper direction towards the glottis in order to move freely through the laryngoscopic channel. Shape and direction are important in controlling the endotracheal tip and for successful intubation.
A practical means of providing and maintaining the endotracheal tube with a prescribed shape is to routinely employ a stylet within the endotracheal tube lumen. When properly combined and conformed, the endotracheal tube and stylet form a working unit—the oral tracheal stylet unit to be used for every routine intubation. 2
Does this approach to intubation, used safely and successfully over many years, expand the nature of investigations needed to develop the editorial suggestion “Common Practice and Concepts in Anesthesia: Time for Reassessment”3and help highlight the essential relationships between the airway, laryngoscopy, and tracheal intubation?