Airway Assessment

Airway assessment is the bedside science of predicting which patient will be difficult to ventilate or intubate before induction of anaesthesia. NEET PG loves the scoring systems (Mallampati, Wilson), the precise cut-off values (thyromental distance, mouth opening, inter-incisor gap) and the definitions framed by the ASA Difficult Airway Task Force. Master the numbers and the mnemonics and this becomes a free mark.

Why it matters

A failed/difficult airway remains one of the leading causes of anaesthesia-related morbidity and mortality (hypoxic brain damage, death). Because most airway disasters occur in patients in whom difficulty was not anticipated, every patient must be screened. The aim of preoperative assessment is to convert an unanticipated difficult airway into an anticipated one, so that the plan, equipment and skilled help are ready.

High-yield: The single most important purpose of airway assessment is to anticipate difficulty so an awake/elective fibreoptic technique can be chosen rather than risking a "can't intubate, can't oxygenate" (CICO/CVCI) situation after induction.

Key definitions (ASA)

Term	Definition
Difficult mask ventilation	Inability of a trained anaesthetist to maintain SpO₂ > 90% with 100% O₂, or to prevent/reverse signs of inadequate ventilation by mask
Difficult laryngoscopy	Inability to visualise any portion of the vocal cords after multiple attempts at conventional laryngoscopy
Difficult intubation	Proper insertion of the tracheal tube requires > 3 attempts or > 10 minutes
Failed intubation	Failure to place the endotracheal tube after multiple attempts
CICO / CVCI	Can't intubate, can't oxygenate / can't ventilate — the airway emergency that mandates emergency front-of-neck access

High-yield: Difficult intubation classically = more than 3 attempts OR more than 10 minutes to intubate.

The history: predictors you must ask about

Before touching the patient, history flags difficulty:

• Previous difficult intubation — strongest single predictor; review old anaesthetic records.
• Congenital syndromes — Pierre Robin (micrognathia, glossoptosis, cleft palate), Treacher Collins, Goldenhar, Down syndrome (large tongue, atlanto-axial instability), Klippel-Feil (fused cervical vertebrae).
• Acquired — obesity/OSA, acromegaly, rheumatoid arthritis (atlanto-axial subluxation, cricoarytenoid involvement), ankylosing spondylitis (fixed flexed neck), scleroderma (restricted mouth opening), burns/radiation/neck surgery scarring, tumours, abscess (Ludwig's angina), pregnancy (oedema, breast enlargement).
• Symptoms — snoring, stridor, hoarseness, dysphagia, dyspnoea positional change.

Bedside examination — the core of NEET PG questions

1. Modified Mallampati classification

Patient sitting, head neutral, mouth opened maximally, tongue protruded, without phonation. Grade by the structures visible:

Class	Structures seen
Class I	Soft palate, uvula, fauces, both pillars (tonsillar pillars)
Class II	Soft palate, uvula, fauces (pillars hidden by tongue base)
Class III	Soft palate + base of uvula only
Class IV	Only hard palate visible; soft palate not seen

High-yield: Classes III and IV predict difficult intubation. The original Mallampati had 3 classes; Samsoon and Young added Class IV → the "modified" classification used today.

Mnemonic for what disappears: "Pillars → Uvula → Soft palate" vanish as the class worsens.

2. Thyromental distance (Patil's test)

Distance from the mentum (chin) to the thyroid notch with the neck fully extended.

• Normal > 6.5 cm (roughly 3 ordinary finger-breadths).
• < 6 cm → difficult intubation likely.
• Reflects the mandibular space available to displace the tongue during laryngoscopy.

3. Sternomental distance

Tip of chin → sternal notch, neck fully extended, mouth closed.

• < 12.5 cm predicts difficult intubation.

4. Mouth opening / inter-incisor gap

Distance between upper and lower incisors with mouth fully open.

• Normal ≥ 3 cm (≈ 2 finger-breadths).
• < 3 cm → difficult; restricted in TMJ disease, scleroderma, trismus.

5. Inter-incisor / mandibular protrusion test (Upper Lip Bite Test, ULBT)

Ability of lower incisors to bite the upper lip:

Class	Finding
I	Lower incisors bite upper lip above vermilion line
II	Lower incisors bite upper lip below vermilion line
III	Lower incisors cannot bite the upper lip

Class III ULBT predicts a difficult airway (tests mandibular protrusion / TMJ mobility).

6. Atlanto-occipital (neck) extension

Normal extension is ~35°. Reduced in ankylosing spondylitis, rheumatoid arthritis, cervical fusion. Limits the ability to achieve the "sniffing" position.

High-yield: No single bedside test is sufficiently sensitive AND specific. Use a combination (Mallampati + thyromental distance + mouth opening) — combined tests have far better predictive value than any one alone.

Wilson risk score

A composite weighted score using five factors, each scored 0–2 (max 10):

Factor	0	1	2
Weight	< 90 kg	90–110 kg	> 110 kg
Head/neck movement	> 90°	~90°	< 90°
Jaw (mouth opening + subluxation)	IIG ≥ 5 cm / subluxation +ve	IIG < 5 cm & subluxation = 0	IIG < 5 cm & subluxation −ve
Receding mandible	Normal	Moderate	Severe
Buck teeth (protruding)	Normal	Moderate	Severe

High-yield: A Wilson score ≥ 2 predicts ~75% of difficult intubations. Mnemonic: "WHJRB" → Weight, Head/neck Movement, Jaw, Receding mandible, Buck teeth.

The "1-2-3 / LEMON / 3-3-2" approach

A quick screen, especially in emergency/ED settings:

LEMON

1. L — Look externally (facial trauma, beard, large incisors, big tongue).
2. E — Evaluate the 3-3-2 rule.
3. M — Mallampati.
4. O — Obstruction/Obesity.
5. N — Neck mobility.

3-3-2 rule (in patient's finger-breadths):

• 3 fingers between the incisors (mouth opening).
• 3 fingers between the tip of chin and the hyoid (mandibular space).
• 2 fingers between the floor of mouth (hyoid) and thyroid notch (larynx position).

Inability to meet any of these predicts difficulty.

Predicting difficult MASK ventilation — "MOANS / OBESE"

Difficult intubation ≠ difficult mask ventilation; assess both.

MOANS (difficult bag-mask ventilation):

• M — Mask seal (beard, blood, facial deformity)
• O — Obesity / Obstruction (BMI > 26)
• A — Age > 55 years
• N — No teeth (edentulous)
• S — Stiff lungs / Snoring (OSA)

High-yield: The classic independent predictors of difficult mask ventilation = Beard, Edentulous, BMI > 26, Age > 55, Snoring/OSA (often remembered as BONES or the "5 predictors"). An edentulous patient is harder to mask-ventilate but easier to intubate.

Intra-operative grading — Cormack–Lehane

This is a laryngoscopic grade (assessed during direct laryngoscopy, not preoperatively), but examiners pair it with assessment:

Grade	View at laryngoscopy
I	Full view of glottis (vocal cords)
II	Only posterior commissure / arytenoids (IIa: partial cords; IIb: only arytenoids)
III	Only epiglottis visible (IIIa: liftable; IIIb: adherent)
IV	Neither glottis nor epiglottis seen

High-yield: Cormack–Lehane Grades III and IV = difficult laryngoscopy. Mallampati predicts before, Cormack–Lehane describes during.

Stepwise approach when difficulty is ANTICIPATED

When preoperative assessment flags a difficult airway, the safest plan keeps the patient breathing spontaneously and protects against loss of oxygenation:

Anticipated difficult airway → optimise & plan → awake technique preferred → topicalise/sedate → awake fibreoptic intubation (gold standard) → confirm tube placement (capnography) → induce after the airway is secured.

A numbered decision flow:

1. Recognise difficulty on assessment (combination of tests).
2. Call for help + prepare difficult airway cart (multiple blade sizes, bougie, video laryngoscope, supraglottic airways/LMA, fibreoptic scope, cricothyrotomy kit).
3. Pre-oxygenate thoroughly (3 min tidal breathing or 8 vital-capacity breaths).
4. Choose awake intubation (fibreoptic) when difficulty is high and certain.
5. If proceeding asleep, ensure ability to wake the patient and maintain mask ventilation.
6. Have a failed-intubation drill ready → LMA/SGA → if CICO → emergency front-of-neck access (cricothyroidotomy).

High-yield: The awake fibreoptic bronchoscope-guided intubation is the gold standard / technique of choice for the anticipated difficult airway because oxygenation and spontaneous ventilation are preserved throughout.

Unanticipated difficult intubation — the rescue ladder

Plan A (tracheal intubation) → optimise position, external laryngeal manipulation (BURP), bougie, video laryngoscope (max 3 + 1 attempts) → Plan B (supraglottic airway, e.g. 2nd-generation LMA to oxygenate) → Plan C (face-mask ventilation, wake the patient if possible) → Plan D / CICO → emergency front-of-neck access (scalpel cricothyroidotomy).

• BURP manoeuvre = Backward, Upward, Rightward Pressure on the thyroid cartilage to improve glottic view.
• Bougie (Eschmann introducer) — feel for tracheal "clicks" and "hold-up" to confirm tracheal placement.

Investigations / adjuncts

Airway assessment is overwhelmingly clinical/bedside; investigations are selective:

• Indirect/flexible nasendoscopy — for laryngeal pathology, tumours.
• Neck X-ray / soft-tissue lateral — retropharyngeal swelling, foreign body, tracheal deviation.
• CT/MRI — masses, airway compression, mediastinal involvement.
• Flow-volume loops — distinguish variable intra- vs extra-thoracic obstruction.
• Cervical spine imaging — rheumatoid arthritis (atlanto-axial subluxation), trauma.

Complications of an unrecognised difficult airway

• Hypoxaemia → hypoxic brain injury, cardiac arrest, death.
• Aspiration of gastric contents (esp. repeated attempts, full stomach).
• Airway trauma — dental damage, lip/tongue laceration, pharyngeal/oesophageal perforation.
• Oesophageal intubation (fatal if unrecognised — hence capnography is mandatory to confirm placement).
• Laryngospasm, bronchospasm, negative-pressure pulmonary oedema.
• Surgical airway complications (bleeding, false passage).

High-yield: Continuous waveform capnography (EtCO₂) is the gold standard to confirm correct tracheal tube placement — "no trace = wrong place." This is repeatedly examined.

Key differentials / look-alikes

• Difficult ventilation vs difficult intubation — assess separately; some patients are easy to intubate but hard to mask (and vice versa).
• Anticipated vs unanticipated — drives whether you choose awake fibreoptic vs a rescue drill.
• Upper vs lower airway obstruction — stridor (inspiratory = supraglottic/extrathoracic; expiratory = intrathoracic) helps localise.
• Mallampati (predictive) vs Cormack–Lehane (descriptive at laryngoscopy) — a classic distractor pairing.

Recently asked / exam angle

• "Which structures are visible in Mallampati Class III?" → Soft palate + base of uvula only.
• "Normal thyromental distance?" → > 6.5 cm; difficult if < 6 cm.
• "Components of Wilson score?" → Weight, Head/neck movement, Jaw, Receding mandible, Buck teeth.
• "Definition of difficult intubation?" → > 3 attempts or > 10 minutes.
• "Who added the 4th class to Mallampati?" → Samsoon and Young.
• "Cormack–Lehane grade indicating difficulty?" → III and IV.
• "Best/most reliable confirmation of tracheal tube?" → Capnography (EtCO₂).
• "Technique of choice for anticipated difficult airway?" → Awake fibreoptic intubation.
• "Sternomental distance cut-off?" → < 12.5 cm.
• "3-3-2 rule values?" → 3 (mouth), 3 (chin–hyoid), 2 (hyoid–thyroid notch).
• "Predictors of difficult mask ventilation?" → Beard, Obese, Aged, No teeth (edentulous), Snorer/OSA.
• "BURP stands for?" → Backward Upward Rightward Pressure.

Rapid revision

1. Mallampati: sitting, mouth open, tongue out, no phonation; III & IV = difficult.
2. Class IV Mallampati → only hard palate seen; added by Samsoon & Young.
3. Thyromental distance > 6.5 cm is normal; < 6 cm difficult (Patil's test).
4. Mouth opening (inter-incisor) ≥ 3 cm normal; < 3 cm difficult.
5. Sternomental distance < 12.5 cm predicts difficulty.
6. Wilson score ≥ 2 = difficult; factors = W-H-J-R-B.
7. 3-3-2 rule: 3 incisors, 3 chin-to-hyoid, 2 hyoid-to-thyroid notch.
8. Difficult mask ventilation: B-O-N-E-S / MOANS (Beard, Obese, No teeth, Elderly, Snoring).
9. Cormack–Lehane III & IV = difficult laryngoscopy (assessed during DL).
10. Difficult intubation = > 3 attempts or > 10 min.
11. Awake fibreoptic intubation = gold standard for anticipated difficult airway.
12. Capnography confirms ETT placement — "no trace = wrong place"; CICO → cricothyroidotomy.