To the Editor:—
We read with interest the article by Adnet et al.1
entitled “Study of the ‘Sniffing Position’ by Magnetic Resonance Imaging.” Although we agree with the authors’ conclusion that in awake patients with normal airway anatomy, the sniffing position does not achieve alignment of the three anatomic axes as defined by them (mouth axis [MA], pharyngeal axis [PA], and laryngeal axis [LA]), we disagree with their assessment that there is no significant difference between anatomic angles observed in simple head extension versus
the sniffing position. Any head extension from the neutral position on a flat surface inevitably results in a degree of neck flexion, hence, the sniffing position. Furthermore, Bannister and Macbeth 2
as a procedural improvement recommended using the sniffing position during direct laryngoscopy; therefore, analysis of the effectiveness of Bannister and Macbeth’s 2
sniffing position for orotracheal intubation without the use of a laryngoscope is unreasonable.
The three anatomic spaces of the airway conduit, beginning at the mouth, passing through the pharynx, and ending at the laryngeal inlet, are not in a straight line. The pathway of this conduit changes its course from one segment to the next; hence, an axis may be assigned to each of these segments: laryngoscopic mouth axis (LMA), laryngoscopic pharyngeal axis (LPA), and laryngoscopic laryngeal axis (LLA) (fig. 1A
). The pharynx extends from the base of the skull to the lower border of the cricoid cartilage, and the laryngeal inlet is located caudal and inferior to the inlet of the mouth. Repositioning the patient’s head from the neutral position (fig. 1A
) to the sniffing position (fig. 1B
) may result in improved alignment of the LMA with both the LPA and LLA. However, adjustment of the position of the head and neck alone is not sufficient to align the three laryngoscopic axes; implementation of a laryngoscope is necessary for the creation of a straight line. The anteriad and caudad force exerted by a laryngoscope blade on the oropharyngeal structures of a patient with his or her head in the sniffing position not only displaces the soft tissues of the oropharyngeal cavity via
the conversion of a potential space to an actual space, but also aligns the laryngoscopic axes resulting in visualization of the vocal cords. The complete alignment of these three axes results in a laryngoscopic line (LL) (fig. 1C
), which we define as a straight line passing through the inferior extremity of the superior incisors and the center of the vocal cords. In contradistinction to the three anatomic axes described by Adnet et al.
these three laryngoscopic
axes (LMA, LPA, LLA) may be aligned and more closely represent a clinically relevant goal to be sought during orotracheal intubation. Therefore, during direct laryngoscopy, the only pertinent maneuver (head positioning) is that which facilitates the production of an LL by improving alignment of the LMA, LPA, and LLA. The true benefit of the sniffing position is that it assists the laryngoscopist in producing an LL. However, contrary to the authors’ conclusion, the sniffing position is superior to simple head extension. Not surprisingly, their results (table 1) 1
do not show any significant change in the angles of the anatomic axes when comparing their simple head extension to the sniffing position.
Bannister and Macbeth 2
never gave a distinct definition of their “anatomical” axes used for alignment; their objective was to improve airway conduit alignment and visualization of the vocal cords. Because their alignment relies on the use of a laryngoscope and manipulation of the patient’s head position, we believe they aligned the laryngoscopic axes, not the anatomic axes, as described by Adnet et al.1
Consequently, Adnet et al.1
should have taken into consideration the effect that a laryngoscope exerts on the anatomic structures comprising the oropharyngeal cavity during direct laryngoscopy. Therefore, we believe that although the anatomic axes described by Adnet et al.1
cannot be aligned, our three laryngoscopic axes can be, and the best position for doing so remains the sniffing position as described by Bannister and Macbeth 2
in 1944. The optimal head positioning for direct laryngoscopy and orotracheal intubation, the so-called sniffing position, remains the true “cornerstone of training in anesthesiology” in 2001, just as it was 57 yr ago.
The authors thank Mr. Billie Roberts, R.T., M.R. (Radiologic Technologist, Magnetic Resonance), and Ms. Toni Roberts, R.T., M.R. (Radiologic Technologist, Magnetic Resonance), of Cook County Hospital, Chicago, Illinois, for organizing the series of magnetic resonance imaging scans for this letter.
Kenneth D. Candido, M.D.
Ahmed H. Ghaleb, M.D.
Simin Saatee, M.D.
Arjang Khorasani, M.D.*
1. Adnet F, Borron SW, Dumas JL, Lapostolle F, Cupa M, Lapandry C: Study of the “sniffing position” by magnetic resonance imaging. A nesthesiology 2001; 94: 83–6
2. Bannister FB, Macbeth RG: Direct laryngoscopy and tracheal intubation. Lancet 1944; 2: 651–4
© 2001 American Society of Anesthesiologists, Inc.