Difficult Airway Assessment
How to anticipate a difficult airway before induction — LEMON criteria, clinical interpretation, and airway planning.
Level 1 — Quick Learn
Medical students and junior residents
What is LEMON?
LEMON is a simple bedside assessment used to predict difficult laryngoscopy and intubation before airway management.
LEMON is not a scoring system — it is a structured way of thinking about airway risk.
L — Look externally
Check for visible features that may suggest difficulty:
- Facial abnormalities
- Obesity
- Beard
- Short neck
- Poor dentition
These features may interfere with mask ventilation or laryngoscopy.
E — Evaluate (3-3-2 rule)
Assess airway geometry using finger breadths:
- Mouth opening — ≥3 finger breadths
- Mandibular space — ≥3 finger breadths
- Thyromental distance / laryngeal position — ≥2 finger breadths
Reduced space suggests limited room for laryngoscope manipulation.
M — Mallampati classification
Evaluate visibility of oropharyngeal structures. Higher class (III–IV) suggests:
- Limited visualization of the glottis
- Increased difficulty in glottic exposure
O — Obstruction
Look for conditions such as:
- Tumors
- Infection
- Edema
Obstruction may cause difficulty in ventilation and inability to intubate — this is a high-risk finding.
N — Neck mobility
Assess ability to extend the neck. Limited mobility prevents alignment of:
- Oral axis
- Pharyngeal axis
- Laryngeal axis
This makes laryngoscopy more difficult.
How to interpret LEMON
No single finding defines a difficult airway. Risk increases when:
- Multiple abnormalities are present
- Or critical findings exist — such as obstruction
Clinical meaning
LEMON does not answer: 'Is intubation possible?' It helps answer: 'How should I prepare?'
Key takeaway
LEMON is not about prediction alone — it is about preparation.