Letters to the Editor: Letters & Announcements
To the Editor
I want to clarify a statement made by El-Orbany et al.1 in a recent review wherein they comment that “recently, Greenland et al.2 performed a magnetic resonance imaging (MRI) study to evaluate the external auditory meatus–sternal notch relationship as a marker that indicates a proper SP [sniffing position] …. They found better axes alignment in the SP.”
The sniffing position was described >70 years ago as the optimal patient position for direct laryngoscopy.3 The 3-axes alignment theory (TAAT) was based on work in 19442 when the laryngoscope blade was the only device available to anesthesia personnel.
After my study wherein the markers for the sniffing position were delineated, I developed a new airway concept called the “2-curve theory”4,5 to understand the impact that head and neck positioning has, not only on tracheal intubation using laryngoscope blades, but for all airway devices.
After superimposing the 2 curves (solid curved line) and the point of inflection (“X”) onto the original figure examining the markers for the sniffing position, the new figure (Fig. 1) shows anticlockwise rotation of the nasopharyngeal–glottis line (dotted line) with the patient in the sniffing position. This line is identical to the tangent at the point of inflection.
The line of sight with direct laryngoscopy is outside the airway passage. In contrast, when using other devices such as videolaryngoscopes and optical stylets, the operator views the glottis somewhere along the primary and secondary curves, and the TAAT is not applicable. The physical properties of the 2 curves and the point of inflection in various head–neck positions as well as the impact of these airway devices on the latter, provides insight into airway management that the TAAT fails to do. In my view, the 2-curve theory is more comprehensive in understanding all aspects of airway management than is the TAAT.
An appreciation of the airway configuration as 2 curves in various head and neck positions provides the operator with the ability to manage the normal airway and also troubleshoot when it becomes difficult.
Keith Greenland, MBBS, MD, FANZCA, FHKAM
Department of Anaesthesia and Perioperative Medicine
Royal Brisbane & Women's Hospital
Herston, Brisbane, Queensland, Australia
1. El-Orbany M, Woehlck H, Ramez Salem M. Review article: head and neck position for direct laryngoscopy. Anesth Analg 2011;113:103–9
2. Greenland KB, Edwards MJ, Hutton NJ. External auditory meatus–sternal notch relationship in adults in the sniffing position: a magnetic resonance imaging study. Br J Anaesth 2010;104:268–9
3. Bannister F, Macbeth R. Direct laryngoscopy and tracheal intubation. Lancet 1944;244:651–4
4. Greenland K. The sniffing and extension–extension position: the need to develop the clinical relevance. Anaesthesia 2008;63:1013–4
5. Greenland KB, Edwards MJ, Hutton NJ, Challis VJ, Irwin MG, Sleigh JW. Changes in airway configuration with different head and neck positions using magnetic resonance imaging of normal airways: a new concept with possible clinical applications. Br J Anaesth 2010;105:683–90