Guide — Airway Management
Difficult Airway Assessment
The time to plan and prepare for a difficult airway is before the attempt, not in the middle of a failing one. This guide covers the predictors — LEMON, the 3-3-2 rule, Mallampati, and the mask and supraglottic mnemonics — the difficult-airway algorithm, and where video laryngoscopy and the rescue devices fit.
9 min read · Airway Management
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
Overview
Predicting airway difficulty matters because the time to plan and prepare is before the attempt, not during a failing one. A structured screen lets the team anticipate the hard intubation, stage the right equipment, choose an awake technique when appropriate, and brief a plan B and plan C — all before the first laryngoscopy rather than scrambling after it.
The predictors come as a small set of mnemonics: LEMON and the 3-3-2 rule for the intubation itself, the Mallampati classes for the oropharyngeal view, and MOANS and RODS for the mask and supraglottic backups. For the respiratory therapist, recognizing these signs and preparing the difficult-airway cart is the contribution that most changes how the attempt goes.
Key Concepts
LEMON is the workhorse screen for a difficult intubation — five elements, each a quick bedside observation.
| Letter | Assessment |
|---|---|
| L | Look externally — facial trauma, beard, large tongue, obesity, abnormal anatomy |
| E | Evaluate 3-3-2 — 3 fingers mouth opening, 3 fingers floor-of-mouth (hyomental), 2 fingers thyrohyoid |
| M | Mallampati — class I to IV view of the oropharynx |
| O | Obstruction / Obesity — anything narrowing or crowding the airway |
| N | Neck mobility — limited movement predicts difficulty |
The M in LEMON is the Mallampati class — how much of the oropharynx is visible on mouth opening, as a proxy for tongue size. A higher class predicts a more difficult laryngoscopic view.
| Class | Structures visible |
|---|---|
| Class I | Soft palate, fauces, uvula, and pillars all visible |
| Class II | Soft palate, fauces, and uvula visible |
| Class III | Soft palate and base of the uvula visible |
| Class IV | Only the hard palate visible |
Intubation is not the only thing that can be difficult, so the backups have their own screens. MOANS predicts difficult bag-mask ventilation and RODS predicts a difficult supraglottic airway; difficult cricothyrotomy is screened for as well.
| Mnemonic | Predicts | Elements |
|---|---|---|
| MOANS | Difficult bag-mask ventilation | Mask seal, Obesity/Obstruction, Age, No teeth, Stiff lungs |
| RODS | Difficult supraglottic airway placement | Restricted opening, Obstruction, Distorted anatomy, Stiff lungs |
| LEMON | Difficult laryngoscopy / intubation | Look, Evaluate 3-3-2, Mallampati, Obstruction, Neck mobility |
Assessment & Findings
When the screen flags difficulty, the approach follows a difficult-airway algorithm such as the ASA pathway — built around keeping the patient oxygenated while the team works through its options.
- Call for help early. An anticipated difficult airway is a team event. Summon additional skilled hands and the difficult-airway equipment before starting, not once an attempt has already failed.
- Keep the patient oxygenated. Oxygenation is the governing priority throughout the algorithm. Between attempts, return to mask or supraglottic ventilation rather than pressing on through desaturation.
- Consider an awake technique. When the airway looks genuinely difficult, securing it while the patient keeps breathing — an awake approach — can be safer than committing to apnea after induction.
- Move through plan A, B, and C. Have a defined sequence: a primary plan, a backup, and a rescue. The point of naming them in advance is to move decisively rather than improvising under pressure.
- Recognize CICO and escalate. The can’t-intubate-can’t-oxygenate situation escalates to a supraglottic rescue and then a surgical airway by cricothyrotomy. Video laryngoscopy improves the glottic view and is a first-line tool for the anticipated difficult airway.
RT Priorities / Interventions
The RT recognizes the predictors, prepares the difficult-airway cart, preoxygenates thoroughly, supports oxygenation throughout, and anticipates the rescue steps.
- Recognize the predictors. Run LEMON and the 3-3-2 rule, note the Mallampati class, and flag the MOANS and RODS features so the whole team knows a difficult airway is expected before induction.
- Prepare the difficult-airway cart. Have the video laryngoscope, a bougie, supraglottic devices, and a surgical airway kit out and checked — the rescue tools staged before, not searched for during.
- Preoxygenate thoroughly. Maximize the oxygen reserve before the attempt so there is the widest possible margin of safe apnea time when the airway proves hard.
- Support oxygenation and anticipate the rescue. Maintain oxygenation between attempts and stay a step ahead of the algorithm — ready to hand over the supraglottic device or the surgical kit the moment the plan moves to rescue.
Common Pitfalls
- Not assessing before attempting. Skipping the screen forfeits the entire advantage of prediction — the team discovers the difficulty mid-attempt, when the options are narrowest.
- Removing oxygenation in a CICO panic. Pulling the supraglottic device or abandoning ventilation when things go wrong removes the one thing keeping the patient alive. Keep oxygenating.
- Fixating on repeated laryngoscopy. Another look at the cords while the saturation falls is the classic error. Oxygenate and move to the rescue rather than taking attempt after attempt.
- Having no backup plan. Walking in with only plan A leaves nowhere to go when it fails. The backup and the rescue must be defined — and staged — before the first attempt.
Board Exam Pearls
- Know LEMON and the 3-3-2 rule — 3 fingers mouth opening, 3 fingers floor-of-mouth, 2 fingers thyrohyoid.
- Mallampati runs I to IV; a higher class predicts a worse laryngoscopic view.
- MOANS predicts difficult mask ventilation; RODS predicts a difficult supraglottic airway.
- CICO escalates to cricothyrotomy — the surgical airway is the end of the rescue pathway.
- Keep oxygenating between attempts, and reach for video laryngoscopy first line in the anticipated difficult airway.
FAQ
What does the LEMON assessment evaluate?
LEMON is a structured bedside screen for a difficult intubation. L is Look externally for features such as facial trauma, a beard, a large tongue, obesity, or abnormal anatomy. E is Evaluate the 3-3-2 rule of mouth opening and jaw geometry. M is the Mallampati class. O is Obstruction or Obesity. N is Neck mobility, where limited movement predicts difficulty. Taken together the elements estimate, before the attempt, how hard the laryngoscopy is likely to be.
What is the 3-3-2 rule?
The 3-3-2 rule is the E in LEMON — a quick finger-based estimate of the geometry that allows a laryngoscopic view. It checks 3 fingers of mouth opening between the incisors, 3 fingers along the floor of the mouth from the chin to the hyoid (the hyomental distance), and 2 fingers from the hyoid to the thyroid notch (the thyrohyoid distance). Falling short on any of the three suggests the anatomy will make aligning the airway axes and seeing the cords more difficult.
What do the Mallampati classes describe?
The Mallampati classification grades how much of the oropharynx is visible when the patient opens the mouth and protrudes the tongue, as a proxy for tongue size relative to the oral cavity. Class I shows the soft palate, fauces, uvula, and pillars; class II shows the soft palate, fauces, and uvula; class III shows the soft palate and the base of the uvula; and class IV shows only the hard palate. A higher class predicts a more difficult laryngoscopic view.
What is the can't-intubate-can't-oxygenate (CICO) pathway?
CICO is the airway emergency in which the patient can be neither intubated nor adequately oxygenated by mask or supraglottic device. It is the failure point a difficult-airway algorithm is built to avoid, and once reached it demands immediate escalation: call for help, place or optimize a supraglottic airway as a rescue, and if oxygenation still fails proceed to a surgical airway by cricothyrotomy. The governing priority throughout is oxygenation, not another look at the cords.
Put it to work
The airway assessment starts well before the laryngoscope — it starts with recognizing the patient whose gas exchange is failing and who will need the airway. Work a blood gas through the interpreter to read that deterioration.
Open the ABG Interpreter →Related Resources
Sources
- Apfelbaum JL, Hagberg CA, Connis RT, et al. 2022 American Society of Anesthesiologists practice guidelines for management of the difficult airway. Anesthesiology. 2022;136(1):31-81.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.