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Difficult Airway Assessment (LEMON)

Estimate the likelihood of difficult laryngoscopy or intubation before induction using the LEMON assessment. Evaluate five airway criteria and receive a risk level with pre-induction strategy guidance.

Based on: ASA 2022 · DAS 2015

Input

L

Look externally

Facial anatomy, jaw geometry, neck profile

Receding jaw, large incisors, beard, short or thick neck, facial trauma

E

Evaluate 3-3-2

Mouth opening / hyoid-mental distance / thyromental distance

Inter-incisor ≥3, hyomental ≥3, thyromental ≥2 finger breadths

M

Mallampati

Mouth wide open, tongue fully extended, no phonation

Class III or IV indicates difficult glottic view

O

Obstruction

Any process physically narrowing or blocking the airway

Epiglottitis, peritonsillar abscess, neck hematoma, foreign body, tracheal stenosis

N

Neck mobility

Can the patient extend the neck for the sniffing position?

Limited by: ankylosing spondylitis, rheumatoid arthritis, cervical surgery, obesity, collar

Overview

Systematically evaluate difficult intubation risk before induction. Five LEMON criteria — each targeting a different anatomical constraint. A structured prompt for airway planning, not a diagnostic certainty.

Evidence Summary

LEMON assessment

LEMON evaluates five independent anatomical constraints: external look, 3-3-2 geometry, Mallampati class, obstruction, and neck mobility. Two override conditions — Mallampati IV and obstruction — result in High risk regardless of total score.

  • Mallampati III–IV: sensitivity 60–70%, specificity 80–90% for difficult laryngoscopy
  • Multiple findings compound risk — each abnormality narrows the margin for error
  • Primary goal is oxygenation, not intubation success (ASA 2022, DAS 2015)

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