Airway Assessment

RE-EXAMINING THE FOUNDATIONS OF AIRWAY ASSESSMENT AND MANAGEMENT
In airway assessment, the discovery of abnormal signs and symptoms often leads to the
presumption of the “difficult airway”. The determination of an abnormality during the assessment
phase is only the first step towards a working diagnosis. Unless we understand the fundamentals
of airway anatomy, laryngoscopy and intubation, evaluation of an airway is fruitless.
With the advent of supraglottic airway devices, more intuitive video laryngoscopes and other
developments in airway equipment, airway management is becoming easier. This trend could
lead to the incorrect assumption that airway assessment is less important. This is far from the
truth.
There is a disconnect between assessment and its application. There is a divergence in
teaching between pattern recognition and conceptual understanding. This article presents an
anatomical foundation for successful direct laryngoscopy and tracheal intubation and a model
for structured airway assessment.
I) THE TWO-CURVE THEORY
In 1944, Banister and Macbeth explored the anatomical basis of direct laryngoscopy via the
description of the “three-axis alignment theory” 1 . The three-axis theory was a refinement
of Magill’s formal description of the “sniffing position” as the preferred intubating position 2 .
Although contentious, the theory has been a mainstay of airway teaching 3-8 .
A novel anatomical airway concept was first proposed in 2008 9 . A Bézier spline, consisting
of primary (oro-pharyngeal) and secondary (pharyngo-glotto-tracheal) curves, serves as the
foundation of the anatomical model (Figure 1) 10 . The inflection point of these curves occurs
in the laryngeal vestibule – the space from the epiglottis to the glottis 10 . Successful direct
laryngoscopy requires alignment of the primary curve and laryngeal vestibule with the line
of sight 10,11 . Intubation of the trachea is facilitated by alignment of the secondary curve and
laryngeal vestibule 10 .
Figure 1. The airway passage is divided into two curves (primary and secondary).
The meeting point of these curves occurs in the laryngeal vestibule 10 .
37 Airway Assessment