Three Axis Alignment, Two Curve Theory and the Three Column Model


The ‘sniffing the morning breeze position’, better termed ‘ear-to-sternal notch’ positioning, is a combination of atlanto-occipital extension and neck flexion (neck flexion of 35° and face plane extension of 15° is cited as ideal) and is considered optimal for direct laryngoscopy

  • this position was originally described by Chevalier Jackson as the “Boyce-Jackson” position in 1913
  • the position was termed the sniffing position by Magill in 1936

The three axis alignment theory, often used to explain why the ‘sniffing the morning breeze’ position is optimal for direct laryngoscopy, is inadequate. Keith Greenland has proposed a ‘two curve theory’ that better explains the processes involved in optimising the direct laryngoscopy view.


Bannister and MacBeth proposed the 3 axis alignment theory in 1944

  • They proposed that the optimal position for direct laryngoscopy brings the laryngeal axis, the pharyngeal axis and the axis of the mouth into alignment with the line of vision
  • Adnet et al (2001) showed using MRI that this is not achieved by the ‘sniffing’ position (in non-anaesthetised volunteers) — in fact, unless the patient has a flip top head, such alignment is anatomically impossible (see figure from Greenland, 2008 here)


Normal position

  • primary curve is the oropharyngeal curve
  • secondary curve is the pharyngo-glotto-tracheal curve
  • point of inflection is the base of the epiglottis, the tangent of this point is the laryngeal vestibule axis

Successful laryngoscopy and tracheal intubation requires alignment of both curves with the line of sight and the trachea.

Effect of manoeuvres

  • Head lift flattens the secondary curve
  • neck extension flattens the primary curve
  • sniffing position dose both
  • the laryngoscope completes flattening of the primary curve


Two main types of video laryngoscopes (VL):

  • Hyperangulated VL
  • Standard geometry VL

Video laryngoscopes that conform to the primary curve (hyperangulated blades) have great success at visualising the larynx but passing the tube may be difficult

  • the camera at the tip points upwards towards the laryngeal vestibule axis
  • those that conform to the primary curve require a curved stylet, a J with a reverse curve near the tip will work best (e.g. Pentax AirwayScope, Glidescope, C-Mac Dorges blade) – these may be best when inline stabilisation of the cervical spine is performed
  • in other instances those that flatten the primary curve (e.g. C-Mac standard blade) may be best, these require a stylet or bougie that is straight to the tip with a 35 degree ‘hockey stick’ bend at the tip (coude tip)


  • Lee LC. Two curves theory does not clearly explain laryngoscopy and intubation. Br J Anaesth. 2011 Jun;106(6):909-10; author reply 910-1. PubMed PMID: 21576102.


The Three Column Model, developed by Keith Greenland (2008), groups the anatomical structures that affect airway management into 3 columns and can be used:

  • as a framework for assessing the airway and prediction of difficult airways
  • to predict which devices are useful for intubation

Posterior column (aka ‘posterior complex’)

  • comprised of structures posterior to the upper airway, particularly the cervical spine
  • affects the ability to position the head and neck in the optimum position for laryngoscopy, which Greenland calls the ‘static phase’ of layrngoscopy
  • optimum positioning requires flexion the lower cervical spine and extension of the occipito-atlanto-axial complex

Middle column (aka ‘air passage’ )

  • pathology affecting the lumen of the the airway

Anterior column (aka ‘anterior complex’)

  • a triangular-shaped pyramid that contains the submandibular space, glossal muscles and laryngeal skeleton
    • has vertices at the temporo-mandibular joints and the lower incisors, with the apex at the hyoid
    • the upper border is formed by the superior surface of the tongue
    • see diagram here from Greenland, 2008
  • the anterior column is displaced by the laryngoscope when it is placed in the mouth and moved in an attempt to expose the glottis; Greenland calls this the ‘dynamic phase’ of laryngoscopy (mouth opening and movement of the laryngoscope to achieve glottic exposure)
  • the anterior column is affected by any pathology that decreases the size of the pyramid or decreases the compliance of the tissues within it, as well as the range-of-movement at the temporomandibular joints and the stylohyoid ligament


  • Posterior column
  • Middle column
  • Anterior column

Posterior column

  • Assessment
    • assess range-of-movement at atlanto-occipital joint (flexion-extension)
  • Examples of pathology
    • rheumatoid arthritis
    • ankylosing spondylitis
    • cervical spine fusion
    • Halo
    • hard cervical spine collar
    • manual in-line stabilisation (MILS)
  • Suggested devices
    • hyperangulated blade video laryngoscopy
    • Direct laryngoscopy with a McCoy blade
    • LMA as a conduit with bronchoscope and Aintree catheter
    • ILMA

Middle column

  • Assessment
    • History and examination (e.g. hoarse voice, stridor)
    • CT/ MRI
    • nasopharyngoscopy
  • Examples of pathology
    • foreign bodies
    • tumours
    • infections, such as abscesses or epiglottitis
    • obstructive sleep apnoea
    • laryngeal oedema
    • upper airway burns
  • Suggested devices
    • Standard blade video laryngoscopy
    • Direct laryngoscopy with a Macintosh blade
    • LMA as a conduit with bronchoscope and Aintree catheter
    • (Avoid ILMA)

Anterior column

  • Assessment
    • thyromental distance, TMJ-TMJ distance, TMJ-to-incisor distance
    • overbite/ micrognathia
    • Mallampati score
  • Examples of pathology
    • decreased size of the anterior column: micrognathia, Marfan’s
    • decreased compliance: Ludwig’s angina, haemorrhage, radiotherapy
    • forward protruding upper incisors (“relative micrognathia”)
    • macroglossia
  • Suggested devices
    • hyperangulated blade video laryngoscopy (conforms to primary curve rather than compresses the anterior column)
    • Direct laryngoscopy with a straight blade (directly lifts epiglottis, narrow profile, compresses the anterior column)
    • LMA as a conduit with bronchoscope and Aintree catheter
    • (Avoid McCoy blade)
    • (Avoid ILMA)

Journal articles and textbooks

  • Adnet F, Borron SW, Dumas JL, Lapostolle F, Cupa M, Lapandry C. Study of the “sniffing position” by magnetic resonance imaging. Anesthesiology. 2001 Jan;94(1):83-6. PubMed PMID: 11135726.
  • Adnet F, Borron SW, Lapostolle F, Lapandry C. The three axis alignment theory and the “sniffing position”: perpetuation of an anatomic myth? Anesthesiology. 1999 Dec;91(6):1964-5. PubMed PMID: 10598648. [free full text]
  • Greenland KB. Airway assessment based on a three column model of direct laryngoscopy. Anaesthesia and intensive care. 2010; 38(1):14-9. [pubmed]
  • Greenland KB. A proposed model for direct laryngoscopy and tracheal intubation. Anaesthesia. 63(2):156-61. 2008. [pubmed] [free full text]
  • Greenland KB, Eley V, Edwards MJ, Allen P, Irwin MG. The origins of the sniffing position and the Three Axes Alignment Theory for direct laryngoscopy. Anaesth Intensive Care. 2008 Jul;36 Suppl 1:23-7. Review. PubMed PMID: 18724555.
  • Greenland K. The ramped position and its relationship to the 2-curve theory. Anesth Analg. 2011 Dec;113(6):1524-5; author reply 1525. PubMed PMID: 22116972.
  • 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 Nov;105(5):683-90. Epub 2010 Sep 15. PubMed PMID: 20846964. [Free Full Text]
  • Lee LC. Two curves theory does not clearly explain laryngoscopy and intubation. Br J Anaesth. 2011 Jun;106(6):909-10; author reply 910-1. PubMed PMID: 21576102. [Free Full Text]

FOAM and web resources

CCC 700 6

Critical Care


Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.

After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.

He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE.  He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.

His one great achievement is being the father of three amazing children.

On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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