AIRWAY ASSESMENT - ICUNOTES

AIRWAY ASSESMENT

Objectives of airway assessment

Identify a potentially difficult airway.
Anticipate the type of difficulty likely to occur.
Prepare appropriate equipment and personnel.
Develop a primary and alternative airway plan.
Maintain oxygenation throughout airway management.
Reduce airway trauma and complications.
Anticipate difficulty with extubation and reintubation.

No single airway examination test can reliably predict all difficult airways.

Table of Contents

HISTORY

Previous Anaesthetic History

One of the most important components of airway assessment is asking about previous anaesthesia.

Specifically ask about:

Previous difficult intubation
Difficult mask ventilation
Difficult supraglottic airway placement
Multiple intubation attempts
Failed intubation
Previous awake intubation
Airway trauma
Dental injury
Aspiration
Difficult extubation

Medical History

Craniofacial abnormalities	Upper airway pathology	Conditions affecting cervical spine movement	Other important conditions
Micrognathia	Supraglottic tumours	Cervical spine instability	Acromegaly
Retrognathia	Laryngeal tumours	Rheumatoid arthritis	Obstructive sleep apnoea
Pierre Robin sequence	Airway oedema	Ankylosing spondylitis	Morbid obesity
Treacher Collins syndrome	Epiglottitis	Cervical spine trauma	Previous head and neck surgery
Goldenhar syndrome	Peritonsillar abscess	Previous cervical spine sur	Neck radiation
Down syndrome	Retropharyngeal abscess		Burns and contractures
Other congenital craniofacial abnormalities	Ludwig’s angina		Thyroid/neck masses
	Foreign body
	Airway stenosis

LOCAL AIRWAY EXAMINATION

FACE	NOSE	TEETH	ORAL CAVITY	NECK
Micrognathia	Nasal deformity	Loose teeth	Mouth opening	Neck circumference
Retrognathia	Nasal patency	Prominent/buck teeth	Tongue size	Neck length
Facial trauma		Protruding incisors	Palate	Neck mobility
Craniofacial abnormalities		Crowns and bridges	Mandibular size	Masses
Burns/contractures		Dentures	Oropharyngeal space	Scars
		Poor dentition	Masses or lesions	Radiation changes
			Mandibular protrusion	Cervical spine abnormalities

Airway Measurements

Measurement	How measured	Significance
Mouth opening	Inter-incisor distance	Reduced opening may restrict insertion and manipulation of airway devices
Thyromental distance	Mentum → thyroid notch with neck extended	Short distance suggests reduced mandibular space
Hyomental distance	Hyoid bone → mentum, usually with the neck in a neutral position	Short distance may indicate reduced submandibular space and increased difficulty with airway management
Sternomental distance	Mentum → sternal notch with neck extended	Gives information about neck length and extension
Neck mobility	Flexion/extension	Reduced movement may make laryngoscopy difficult
Mandibular protrusion	Ability of lower incisors to move beyond upper incisors	Assesses mandibular mobility

Approximate values used in airway assessment

Parameter	Favourable	Concerning
Mouth opening	>4 cm	<3 cm
Thyromental distance	>6.5 cm	<6 cm
Hyomental distance	>4 cm	<4 cm
Sternomental distance	>12.5 cm	<12 cm

Note: These are approximate clinical thresholds and should not be used in isolation.

Airway assessment TESTS

Always better to use a combination of tests

Oropharynx
Atlanto-Occipital Joint
Submandibular Space
Radiological

Mallampati Classification

Class	Structures visible	Interpretation
I	Soft palate, fauces, uvula and pillars	Generally favourable
II	Soft palate, fauces and part/base of uvula	Generally favourable
III	Soft palate and base of uvula	Increased likelihood of difficult laryngoscopy
IV	Hard palate only	Increased likelihood of difficult laryngoscopy

Important point

Mallampati is a predictor, not a diagnosis of difficult intubation.

It should always be interpreted together with other airway findings

Cormack–Lehane Classification

NOT a preoperative examination; it is an intraoperative laryngoscopic view

Grade	Laryngoscopic view
Grade I	Full view of glottis
Grade II	Partial view of glottis
Grade III	Epiglottis visible but glottis not visible
Grade IV	Neither glottis nor epiglottis visible

Modified classification

Grade	Description
IIa	Partial view of glottis
IIb	Only posterior glottic structures/arytenoids visible
IIIa	Epiglottis visible and can be lifted
IIIb	Epiglottis visible but cannot be lifted

Important distinction

Test	What it tells you
Mallampati	Preoperative airway assessment
Cormack–Lehane	Laryngoscopic view obtained during direct laryngoscopy

Temporomandibular Joint (TMJ) & Mandibular Examination

The TMJ and mandible are assessed because adequate mouth opening and mandibular mobility are important for insertion and manipulation of the laryngoscope and for achieving a good laryngeal view.

Examination / Test	Technique	Normal / Expected Finding	Significance
Inter-incisor distance (mouth opening)	Ask the patient to open the mouth maximally. Measure the distance between the upper and lower incisors.	Usually ≥ 3.5–4 cm	Reduced mouth opening may make insertion and manipulation of the laryngoscope difficult.
Mandibular protrusion	Ask the patient to move the lower jaw as far forward as possible.	Good forward movement of the mandible	Assesses the range of anterior mandibular movement. Restricted protrusion may be associated with difficult laryngoscopy.
Upper Lip Bite Test (ULBT)	Ask the patient to bite the upper lip with the lower incisors.	Class I: lower incisors can bite the upper lip above the vermilion line	Assesses mandibular mobility and dental relationship. Higher classes are associated with increased difficulty.
Delikan test	Ask the patient to protrude the mandible and assess whether the lower incisors can move in front of the upper incisors.	Lower incisors can protrude beyond the upper incisors	Specifically assesses the ability of the mandible to advance anteriorly relative to the maxilla.
TMJ movement	Assess mandibular opening, protrusion and lateral movements. Observe for pain, clicking or restriction.	Full, symmetrical movement without significant restriction	TMJ restriction can reduce mouth opening and mandibular mobility.
Mandibular morphology	Inspect for micrognathia, retrognathia, receding mandible and prominent incisors.	Adequate mandibular size and projection	Small or receding mandible reduces the available submandibular space and may make laryngoscopy difficult.

Are mandibular protrusion and the Delikan test the same?

They are closely related but are not exactly the same.

Mandibular protrusion is a general assessment of how far the patient can move the lower jaw forward.
The Delikan test is a specific assessment of the relationship between the lower and upper incisors during mandibular protrusion—specifically, whether the lower incisors can move in front of the upper incisors.

Therefore, mandibular protrusion describes the movement, whereas the Delikan test assesses the resulting anterior dental relationship.

Key distinction

ULBT: assesses whether the lower incisors can bite the upper lip.
Delikan test: assesses whether the lower incisors can protrude beyond the upper incisors.
Mandibular protrusion: assesses the overall forward movement of the mandible.

Upper Lip Bite Test

Class	Finding
Class I	Lower incisors can bite above the vermilion border of the upper lip
Class II	Lower incisors can bite the upper lip but not above the vermilion border
Class III	Lower incisors cannot reach the upper lip

Significance: Assesses mandibular mobility and ability to subluxate the mandible.Submandibular Space Examination

The submandibular space is extremely important because the tongue must be displaced into this space during direct laryngoscopy.

A small or poorly compliant submandibular space can make tongue displacement difficult.

Examination / Test	How assessed	Significance
Thyromental distance (TMD)	Measure from mentum to thyroid notch with neck extended	Estimates available submandibular space
Sternomental distance (SMD)	Measure from mentum to sternal notch with neck extended	Reflects mandibular/neck dimensions and extension
Mandibular length	Assess mandibular size/profile	Short mandible may reduce available space
Retrognathia / micrognathia	Inspect lateral facial profile	Posterior/small mandible reduces space for tongue displacement
Mandibular protrusion	Ask patient to protrude mandible	Assesses mobility of the mandible

Thyromental Distance

Mentum → thyroid notch

with the neck fully extended.

Approximate value	Interpretation
>6.5 cm	Generally favourable
<6 cm	May indicate increased difficulty

Why is TMD important?

During laryngoscopy, the tongue must be displaced into the submandibular space.

A short thyromental distance suggests:

Short mandible → reduced submandibular space → difficult tongue displacement → potentially difficult laryngoscopy

Atlanto-Occipital Joint Examination

The atlanto-occipital joint (AOJ) allows extension of the head on the cervical spine.

Adequate extension helps position the oral, pharyngeal and laryngeal axes for direct laryngoscopy.

Examination	Technique	Normal / expected	Difficult airway implication
Atlanto-occipital extension	Ask patient to keep the neck relatively fixed and extend the head backward	Approximately 35° extension	Restricted extension → impaired alignment for direct laryngoscopy
Cervical flexion	Ask patient to flex the neck forward	Approximately 40–50° flexion	Restricted flexion → inability to achieve optimal sniffing position
Head & neck positioning	Flex the neck and extend the head	Adequate combined movement	Restricted movement may predict difficult direct laryngoscopy

Conditions associated with restricted AO/cervical movement

Rheumatoid arthritis
Ankylosing spondylitis
Cervical spine trauma
Cervical spine surgery
Cervical spine instability
Advanced degenerative disease

Neck Examination

Examination	What to assess	Significance
Neck circumference	Measure/estimate neck size	Increased circumference associated with difficult airway, particularly in obesity/OSA
Neck length	Short vs long neck	Short thick neck may make airway management difficult
Neck mobility	Flexion and extension	Restricted movement
Neck masses	Thyroid, lymph nodes, tumours	May compress/displace airway
Scars	Previous tracheostomy, neck surgery	Suggest altered anatomy
Radiation changes	Fibrosis, reduced tissue mobility	May make airway manipulation difficult
Cervical spine examination	Stability and movement	Important before airway manipulation

Radiological Airway Examination

Radiological assessment is not routine. It is indicated when structural airway problems are suspected, such as:

Airway obstruction or stenosis
Neck or mediastinal mass
Craniofacial abnormality
Previous airway surgery or radiotherapy
Trauma
Cervical-spine abnormality

Common Imaging Modalities

Investigation	Main uses
Lateral neck X-ray	Upper-airway narrowing, epiglottic swelling, prevertebral swelling, foreign body
AP neck X-ray	Tracheal deviation or compression
Cervical-spine X-ray/CT	Fracture, instability, deformity or limited neck movement
CT neck ± chest	Airway narrowing, stenosis, tumour, abscess, tracheal deviation or compression
3-D CT reconstruction	Defines the site and length of complex airway stenosis
MRI neck	Soft-tissue and vascular involvement, especially in head-and-neck masses
Ultrasound	Superficial neck masses, tracheal position and airway procedures
Fluoroscopy	Dynamic airway collapse or cervical-spine movement

What to Assess

Radiology should determine:

Is the airway narrowed?
Assess the site, length and severity.
Is the airway displaced?
Look for tracheal deviation or distortion.
Is the airway compressed?
Identify masses, tumours, abscesses or mediastinal pathology.
Is neck movement safe?
Assess for cervical-spine instability, fracture or deformity.

Key Point

Radiology is an adjunct to clinical airway assessment, not a replacement.

Clinical examination identifies potential difficulty.
Imaging defines structural anatomy.
Endoscopy directly visualizes the airway.

Predictors of Difficult Mask Ventilation

OBESE mnemonic

Risk factor	Why it matters
Obesity	Increased upper-airway soft tissue and reduced respiratory reserve
Beard	Poor mask seal
Elderly age	Increased risk of difficult mask ventilation
Snoring / OSA	Increased upper-airway collapsibility
Edentulous state	Reduced facial support and mask seal
Facial abnormality	Difficulty obtaining an effective mask seal
Limited neck extension	May impair airway opening and positioning

	Meaning
O	Obese
B	Bearded
E	Elderly
S	Snorer
E	Edentulous

Difficult Supraglottic Airway Placement — RODS

	Meaning	Example
R	Restricted mouth opening	Severe trismus
O	Obstruction	Airway tumour/foreign body
D	Distorted airway	Trauma, surgery, oedema
S	Stiff lungs	High airway resistance/compliance problems

LEMON Airway Assessment

	Component	What to assess
L	Look externally	Facial abnormalities, obesity, prominent teeth, abnormal mandible
E	Evaluate	Mouth opening, thyromental distance and mandibular space
M	Mallampati	Oropharyngeal anatomy
O	Obstruction	Tumour, oedema, infection, abscess, foreign body
N	Neck mobility	Flexion and extension

LM-MAP Approach

Component	Assessment
L – Look	External facial and neck abnormalities
M – Mallampati	Oropharyngeal view
M – Measurements	Mouth opening, thyromental distance and related measurements
A – Atlanto-occipital movement	Neck extension
P – Pathology	Tumour, oedema, infection, obstruction

Wilson Risk Score

The Wilson risk score is a preoperative airway assessment tool used to estimate the likelihood of difficult laryngoscopy and tracheal intubation. It evaluates five factors, each scored from 0 to 2.

Factor	Score 0	Score 1	Score 2
Body weight	Normal or not significantly increased	Moderately increased weight	Markedly increased weight or obesity
Head and neck movement	Full movement	Moderately restricted movement	Severely restricted movement
Prominent maxillary incisors	No prominent incisors	Moderately prominent incisors	Very prominent incisors
Jaw movement	Normal mandibular mobility	Moderately reduced mobility	Severely reduced mobility
Mandibular recession	No recession; normal mandibular projection	Moderate recession	Marked retrognathia or severely receding mandible

Minimum score: 0
Maximum score: 10

The total score is calculated by adding the scores for all five factors:

Wilson score = body weight + head and neck movement + prominent maxillary incisors + jaw movement + mandibular recession

Total score	Interpretation
0–2	Lower likelihood of difficult intubation
3–4	Intermediate or increased risk
≥5	High risk of difficult intubation

A higher score indicates a greater likelihood of difficult laryngoscopy and intubation. The score is particularly concerning when several abnormalities are present together, such as obesity, restricted neck movement, prominent upper incisors, limited mandibular mobility and retrognathia.

Prediction scores support clinical assessment but do not replace it.

Four Ds of Difficult Airway

D	Meaning	Examples
Dentition	Abnormal teeth	Prominent/loose teeth
Distortion	Distorted airway anatomy	Tumour, oedema, blood, infection
Disproportion	Abnormal anatomical proportions	Large tongue, small/receding mandible
Dysmobility	Restricted movement	TMJ or cervical spine restriction