The three axis alignment theory and the "sniffing position": perpetuation of an anatomic myth?

To the Editor:—A review of the classic anesthesiology literature reveals a common thread in the instructions for direct laryngoscopy: To successfully visualize the larynx, one must align three (oral, laryngeal, and pharyngeal) anatomic axes. Placing a patient in the “sniffing position” is the accepted maneuver for aligning these axes. Recently, we evaluated a radiograph obtained during intubation in the sniffing position, drew lines along the axes (fig. 1), and did not observe this alignment. We then reviewed the literature to understand the origin of this concept. The sniffing position has been credited to Chevalier Jackson in 1913, although he did not use this terminology or demonstrate alignment of the axes diagramatically. He simply suggested that the patient be placed on a pillow in a natural position with the head extended. He went on to suggest that, in fact, the pillow might be removed, the thumbs placed on the forehead of the patient, and the forehead vigorously forced downward and backward, causing an anterior movement of the skull on the atlas and throwing the cervical vertebrae forward. After this proposal by Jackson, numerous authors offered their modifications of the technique. However, the first (only?) authors to study the problem experimentally were Bannister and MacBeth, whose frequently cited 1944 Lancet article graphically demonstrates the alignment of the three axes by use of an added pillow beneath the occiput, thus flexing the neck. The authors then propose that straightening the right angle formed by the axis of the mouth and the pharyngolaryngeal axis requires extension of the head on the atlantooccipital joint. They support their view with a series of drawings and radiographs. Although the authors’ drawings illustrate plainly that the axes may be brought into complete alignment, close examination of the radiographs shows that the drawing did not coincide with the radiograph. Whereas the hard palate is aligned with the larynx in the drawing, the angle of the larynx to the hard palate in the radiograph is roughly 36°. If one compares radiographs in the article, it becomes apparent that the laryngoscope shown in one radiograph (patient in sniffing position) is not in the mouth. Otherwise this patient would be missing all the upper incisors. Perhaps this is what was referred to previously in the article as “cooking” a diagram. In spite of this, the “three-axes rule” became reality. It would appear to us that, although the sniffing position may provide the best laryngeal view, the explanation of the benefit of the sniffing position based on alignment of the three axes is an error perpetuated since 1944 that deserves reexamination.