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A Reconsideration of Three Axes Alignment Theory and Sniffing Position

Chou, Hsiu-chin M.D.*; Wu, Tzu-lang M.D.

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To the Editor:—
It is interesting to read the recent study by Adnet et al., 1 its accompanied editorial, and other related reader comments on the “sniffing position.” We applaud the efforts of Adnet et al. in challenging the classic three axes alignment theory 2 and conducting subsequent studies 1,3 to prove their conviction. From our experience as clinicians, we believe the sniffing position is by no means a “gold standard” for laryngoscopy. It is simply one alternative among several techniques, such as laryngeal lift 4 or the BURP 5 maneuver, to facilitate laryngeal visualization in some clinical situations, such as in patients with limited head extension or obesity as found in the study of Adnet et al.1
Adnet et al.2 showed that a successful direct laryngoscopy does not require alignment of the three (oral, pharyngeal, and laryngeal) anatomic axes. Adnet et al.3 further demonstrated that anatomic alignment of the three axes is impossible to achieve in neutral head position, simple head extension, or sniffing position. Adnet et al.1 concluded that the sniffing position is not any better than simple head extension for facilitating direct laryngoscopy. Thus, we are convinced that the three axes alignment theory is invalid and standard practice doctrine must be rewritten. As clinicians, we must ask, what is the mechanism of direct laryngoscopy? How can we explain the benefit of the sniffing position? To this end, we have proposed a “two axes, tongue, mobility, and space” approach, 6 as an outgrowth of the simple original teachings in Gillespie's classic textbook 7:
… In the normal position of the structures the line from the upper incisor teeth through the pharynx to the glottis is almost a right angle. This must be converted into a straight line by the laryngoscope to bring the glottis into the line of vision. To achieve this straight line the base of the tongue and the epiglottis must be lifted anteriorly…. In this (sniffing) position there is no tension on the muscles of the neck, and the distance from the teeth to the glottis is shortened….
We note that there is no hint of a laryngeal axis in Gillespie's teaching of direct laryngoscopy and explanation of sniffing position. In fact, the benefit of the sniffing position may also be illustrated by a simple geometric principle utilizing only the oral and pharyngeal axes. 6
Lastly, from experience, we find that in patients with a short mandibular ramus, 8 the sniffing position may worsen glottic exposure. However, if less head extension and more cervical flexion than usual are exerted, glottic exposure may be improved. We suggest that in patients with a short mandibular ramus, in whom the floor of oral cavity is already high (more toward the skull), 8 maximal head extension not only increases neck muscle tension but also raises the oral cavity floor even higher; thus, the glottis is further away from the teeth. We do not know if the 11% of negative effect of the sniffing position in the study of Adnet et al.1 represents a similar patient group.
Hsiu-chin Chou, M.D.*
Tzu-lang Wu, M.D.
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References

1. Adnet F, Baillard C, Borron SW, Denantes C, Lefebvre L, Galinski M, Martinez C, Cupa M, Lapostolle F: Randomized study comparing the “sniffing position” with simple head extension for laryngoscopic view in elective surgery patients. A nesthesiology 2001; 95: 836–41

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

3. 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

4. Krantz MA, Poulos JG, Chaouki K, Adamek P: The laryngeal lift: A method to facilitate endotracheal intubation. J Clin Anesth 1993; 5: 297–301

5. Knill RL: Difficult laryngoscopy made easy with a “BURP.” Can J Anaesth 1993; 40: 279–82

6. Chou HC, Wu TL: Rethinking the three axes alignment theory for direct laryngoscopy. Acta Anaesthesiol Scand 2001; 45: 261–2

7. Gillespie NA: Endotracheal Anesthesia, 3rd edition. Madison, University of Wisconsin, 1963, pp 76–80

8. Chou HC, Wu TL: Mandibulohyoid distance in difficult laryngoscopy. Br J Anaesth 1993; 71: 335–9

Cited By:

This article has been cited 1 time(s).

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