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HLT-RESP80-05 · Lesson 2 · 32 clock hours · theory

Airway Assessment and Difficult Airway Prediction

Objective. Students will apply standardized airway assessment tools — including the Mallampati classification, thyromental distance, and mouth opening evaluation — to simulated patient scenarios and identify features predicting a difficult airway.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why Airway Assessment Matters

The ability to secure a patient's airway is one of the most critical skills in respiratory therapy. Before any intubation attempt or advanced airway procedure, you must systematically evaluate the patient to predict whether the airway will be easy or difficult to manage. A missed difficult airway can lead to hypoxia, brain injury, or death within minutes. Standardized assessment tools exist precisely to reduce that risk by giving every clinician a shared, repeatable language.

This lesson covers the core assessment tools you will use in clinical practice and that appear on the NBRC CRT and RRT examinations: the Mallampati classification, thyromental distance measurement, and mouth opening evaluation. You will also learn how to combine these findings into a clinical prediction of difficult airway.

The Mallampati Classification

The Mallampati classification is a visual scoring system that estimates how much of the oropharynx is visible when a patient opens their mouth wide and protrudes the tongue without phonating. It predicts the difficulty of visualizing the larynx during laryngoscopy.

How to perform it: Seat the patient upright if possible. Ask the patient to open the mouth as wide as possible and extend the tongue fully without making a sound. Use a penlight to illuminate the oropharynx. Observe which structures are visible.

The four classes:

Mallampati Class III or IV is a recognized predictor of difficult intubation. Document the class on every pre-procedure airway assessment form.

Thyromental Distance

Thyromental distance (TMD) is the straight-line distance from the thyroid notch (the V-shaped notch at the top of the thyroid cartilage) to the tip of the mandible (mentum), measured with the patient's head in the fully extended position and the mouth closed.

How to perform it: Place the patient supine or seated with the neck extended. Use a rigid ruler or tape measure. Place one end at the thyroid notch and the other at the tip of the chin.

Clinical interpretation: A TMD of less than approximately 6 cm (about three finger-breadths) is generally considered a predictor of difficult laryngoscopy, because a short distance indicates limited space for the tongue to displace anteriorly during direct laryngoscopy. A TMD of 6 cm or more is generally reassuring, though it must be interpreted alongside other findings.

Mouth Opening Evaluation

Adequate mouth opening is required to insert a laryngoscope blade and visualize the glottis. The standard measurement is the inter-incisor distance — the gap between the upper and lower incisors (or gum ridges in edentulous patients) when the mouth is opened maximally.

Clinical interpretation: An inter-incisor distance of less than approximately 3 cm (about two finger-breadths) is associated with restricted access for laryngoscopy and can predict a difficult intubation. Also note any jaw abnormalities, limited neck mobility, or restricted temporomandibular joint movement.

Additional Predictors of Difficult Airway

No single test is perfectly predictive. Clinicians use a combination of findings. Additional features to assess and document include:

Difficult Airway Prediction: Putting It Together

A difficult airway is typically defined as a situation in which a trained clinician encounters difficulty with mask ventilation, laryngoscopy, or tracheal intubation. When two or more predictors of difficulty are present, you should alert the supervising physician or licensed practitioner immediately, ensure backup equipment is available, and document your findings.

Scope of practice reminder: As a respiratory therapist, you perform airway assessments and communicate findings to the team. Advanced decisions about airway management strategy are made collaboratively with the physician or advanced practice provider. Never delay alerting the team when you identify a potentially difficult airway.

Safety Points

Key terms8

Mallampati ClassificationA four-class visual scoring system that grades oropharyngeal visibility when the patient opens the mouth maximally and protrudes the tongue; Classes III and IV predict a more difficult laryngoscopic view.
Thyromental Distance (TMD)The straight-line distance from the thyroid notch to the tip of the chin with the neck fully extended; a measurement less than approximately 6 cm suggests limited space for tongue displacement and predicts difficult laryngoscopy.
Inter-incisor DistanceThe maximum gap between the upper and lower incisors (or gum ridges) when the mouth is fully open; less than approximately 3 cm indicates restricted mouth opening and potential intubation difficulty.
Difficult AirwayA clinical situation in which a trained clinician anticipates or encounters difficulty with mask ventilation, laryngoscopy, or tracheal intubation, often due to anatomical or pathological features.
LEMON MnemonicA systematic bedside airway assessment framework: Look externally, Evaluate the 3-3-2 rule, Mallampati score, Obstruction/obesity, Neck mobility.
LaryngoscopyDirect or indirect visualization of the larynx using a laryngoscope blade; the procedure most directly affected by airway anatomy when performing orotracheal intubation.
Faucial PillarsThe paired mucosal folds on either side of the oropharynx flanking the tonsillar area; their visibility is a key landmark in Mallampati classification.
Thyroid NotchThe V-shaped superior depression of the thyroid cartilage; the starting landmark for measuring thyromental distance.

Worked examples4

1. A patient sits upright, opens the mouth wide, and protrudes the tongue. The examiner can see the soft palate, the entire uvula, and both faucial pillars. What Mallampati class is this, and what does it predict?
  1. Step 1: Identify which structures are visible — soft palate, uvula, and faucial pillars are all visible.
  2. Step 2: Match the findings to the Mallampati classification: all four key structures (soft palate, uvula, faucial pillars, tonsillar area) visible = Class I.
  3. Step 3: Interpret the clinical significance: Class I is associated with a generally easy laryngoscopic view and low predicted difficulty with intubation.
Answer: Mallampati Class I. This finding predicts a generally easy airway and favorable laryngoscopic view.
2. You measure a patient's thyromental distance. The thyroid notch to chin tip measures 5.2 cm with the neck fully extended. Is this finding reassuring or concerning, and why?
  1. Step 1: Recall the clinical threshold — a thyromental distance less than approximately 6 cm is considered a predictor of difficult laryngoscopy.
  2. Step 2: Compare the measured value: 5.2 cm is less than 6 cm.
  3. Step 3: Conclude that the finding is concerning — the short distance suggests limited anterior space for tongue displacement during direct laryngoscopy, predicting potential difficulty.
Answer: Concerning. A TMD of 5.2 cm falls below the approximately 6 cm threshold and is a recognized predictor of difficult laryngoscopy.
3. A patient can open their mouth a maximum of 2.4 cm (inter-incisor distance). They are also Mallampati Class III. How many difficult-airway predictors are present, and what action should the respiratory therapist take?
  1. Step 1: Evaluate mouth opening — 2.4 cm is less than the approximately 3 cm threshold, so this is one predictor of difficult intubation.
  2. Step 2: Evaluate the Mallampati class — Class III (soft palate and base of uvula visible, faucial pillars not visible) is a recognized predictor of difficult laryngoscopic view, so this is a second predictor.
  3. Step 3: Count total predictors — two predictors are present (restricted mouth opening + Mallampati Class III).
  4. Step 4: Apply scope-of-practice principles — the respiratory therapist should promptly document both findings, alert the supervising physician or licensed practitioner, and ensure that backup airway equipment is prepared before any intubation attempt.
Answer: Two difficult-airway predictors are present. The respiratory therapist should document the findings, immediately alert the supervising physician, and help ensure backup airway equipment is available.
4. Using the LEMON mnemonic, a student assesses a patient and finds: external appearance normal, mouth opens 3.5 cm, thyroid notch to chin 6.5 cm, floor of mouth to thyroid notch 2.5 cm, Mallampati Class II, no obstruction, and full neck extension. Summarize whether this patient is predicted to have an easy or difficult airway.
  1. Step 1: Look externally — no abnormal features noted (favorable).
  2. Step 2: Evaluate 3-3-2 rule — mouth opening 3.5 cm (≥3, favorable); hyoid-to-chin approximately 6.5 cm (≥3 finger-breadths, favorable); thyroid notch to floor of mouth 2.5 cm (approximately 2 finger-breadths, favorable).
  3. Step 3: Mallampati Class II — slightly elevated but not a high-risk class (mildly elevated).
  4. Step 4: Obstruction/obesity — none noted (favorable).
  5. Step 5: Neck mobility — full extension (favorable).
  6. Step 6: Synthesize findings — all LEMON components are within acceptable ranges or only mildly elevated; no two high-risk predictors are simultaneously present.
Answer: This patient is predicted to have a generally easy airway. Only one mild predictor (Mallampati Class II) is present; all other LEMON components are within normal limits.
In class: Practice Mallampati classification and mouth-opening measurement on fellow students and on standardized patient photographs, recording findings on a structured assessment form. · Review and discuss a set of de-identified case photographs and brief histories; for each case, complete a difficult-airway prediction checklist and propose an airway strategy with rationale. · Participate in a structured class discussion using NBRC-style multiple-choice questions on airway assessment, reviewing answer rationale after each question.
Materials: Standardized patient photographs, difficult-airway prediction checklists, Mallampati reference chart, tongue depressors, penlight, Egan's Fundamentals of Respiratory Care, NBRC content outline
Check: Scored assessment worksheet: student correctly classifies all four Mallampati images and flags ≥90% of difficult-airway indicators in case set; pass = 80% or higher.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Airway Management / Patient Assessment
1. A patient opens the mouth fully and protrudes the tongue. The examiner can see the soft palate but only the base of the uvula; the faucial pillars are not visible. Which Mallampati class does this represent?
Airway Management / Patient Assessment
2. Which thyromental distance measurement would most strongly predict a difficult laryngoscopic intubation?
Airway Management / Patient Safety
3. Only the hard palate is visible when a patient fully opens their mouth and protrudes the tongue. What Mallampati class is assigned, and what clinical action is most appropriate before an elective intubation?
Airway Management / Assessment Technique
4. When measuring thyromental distance, the patient's head should be positioned in which way?
Airway Management / Clinical Decision-Making
5. A patient has a Mallampati Class II airway and an inter-incisor distance of 2.5 cm. How should the respiratory therapist interpret these findings?
Airway Management / Assessment Tools
6. In the LEMON airway assessment mnemonic, what does the letter 'N' represent?
Airway Management / Patient History and Assessment
7. Which of the following patient histories would most increase a respiratory therapist's concern about a potentially difficult airway, independent of current physical examination findings?
Airway Management / Assessment Technique
8. A respiratory therapy student performs a Mallampati assessment on a classmate and records Class I. Later she reassesses the same classmate in a supine position and records Class III. Which statement best explains this discrepancy?
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