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You Can Smell the Difference

Adnet, Frédéric M.D., Ph.D.

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In Reply:—
We appreciate the interest shown in our article, as evidenced by the letters from Drs. Sosis, Candido et al., Froelich, Weinberg, and Lee, regarding the “sniffing position” studied using magnetic resonance imaging. 1 The commentators insist on the need for a clinical (rather than anatomic) evaluation of the sniffing position. First, our study was not intended to evaluate the sniffing position for improvement of the laryngoscopic view during general anesthesia. Our goal was only to demonstrate that the alignment of anatomic axes, as defined by Bannister and Macbeth, 2 was impossible in any of the three head positions tested. We agree with Dr. Sosis that the sum of α and β was numerically lowest in the sniffing position; however, this value was far from zero. Our conclusion that the sniffing position offers no improvement over simple head extension in terms of anatomic alignment of LA, PA, and MA has been challenged because the commentators believe that it does not correspond with the laryngoscopic view. This has no relevance in relation to our study. Again, our goal was not to evaluate the ability of head positioning to facilitate laryngoscopy (and intubation).
The pharyngeal axis is defined in our study as a line joining the anterior portion of the atlas and C2 (as illustrated in figs. 1A–C in the article), which corresponds to the axes drawn (but not defined) in the illustrations of Bannister and Macbeth, 2 who drew the pharyngeal axis as a line parallel to the posterior wall of the pharynx. We agree with Dr. Candido et al. that any head extension from the neutral position on a flat surface will inevitably result in a degree of neck flexion, which we calculated (table 2 in the article) and stated in our article. We have pointed out that the principal limitation of our study was that it was performed in healthy, nonanesthetized volunteers, but we insist (as stated in the Discussion) that first, the determination of anatomic axes and their movements do not necessitate anesthesia or laryngoscopy, and second, that the original study was performed in nonanesthetized patients, apparently without a laryngoscope blade in the mouth. 3 We stand by our assertion.
We were intrigued by the “new” laryngoscopic axes referred to but undefined by Candido et al. We are circumspect of their definition of the pharyngeal axis, but more importantly, we saw no fundamental difference between head extension and the sniffing position on the magnetic resonance images they provide (which incidentally do not illustrate the presence of a laryngoscope).
We agree with Dr. Froelich that our definition of the laryngeal axis is not standardized, but again, the goal of our study was to examine whether the axes that are used in the classic study of Bannister and Macbeth 2 and are disseminated through the general anesthesia literature actually contribute to anatomic alignment in the sniffing position. In the original study, the laryngeal axis is drawn as a straight line situated in the center of the larynx. 2 We have used the same representation of the study of Bannister and Macbeth 2 to define our axes. If one examines the original figure in the neutral position and our figure 1A, it seems that they have the same axes and the same angle between axes. 1,2 The correlation between head position and weight was not evaluated in our study but is relevant to a clinical study.
Finally, contrary to what the commentators would have the reader believe, we never stated that the sniffing position is not superior to simple head extension during laryngoscopy. We have simply observed that, if such a clinical advantage exists, the anatomic explanation cannot be found in the alignment of axes, a concept widely propagated in the literature. Dr. Sosis states that perhaps a more important question for anesthesiologists is, “Does the sniffing position facilitate laryngoscopy and tracheal intubation?” We are pleased that Dr. Sosis recognizes that we did not attempt to answer this question in the study. However, we have recently completed a randomized clinical trial to attempt to answer this question in 456 anesthetized surgical patients, which will be published in an upcoming issue of Anesthesiology.
Frédéric Adnet, M.D., Ph.D.
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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

3. Adnet F, Borron SW, Lapostolle F, Lapandry C: The three axis alignment theory and the “sniffing position”: Perpetuation of an anatomical myth? A nesthesiology 1999; 91: 1964–5

© 2001 American Society of Anesthesiologists, Inc.

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