# Airway Assessment and the Difficult Airway Algorithm

## Airway Assessment

### History

A thorough airway history begins with reviewing previous anesthesia records for prior intubation grade, equipment used, and difficulties encountered. Important historical features include obstructive sleep apnea, snoring, or CPAP use; head and neck surgery, radiation therapy, or trauma; rheumatologic conditions such as rheumatoid arthritis (which can cause atlantoaxial instability and cricoarytenoid arthritis) and ankylosing spondylitis; congenital syndromes including Pierre Robin, Treacher Collins, Down syndrome, and Goldenhar; pregnancy (which causes airway edema, weight gain, and worsening Mallampati class); acromegaly (macroglossia, subglottic narrowing); and morbid obesity (redundant pharyngeal tissue, short thick neck).

### Physical Examination Predictors

#### Mallampati Classification

The Mallampati classification is performed with the patient sitting upright, mouth maximally open, tongue protruded, and without phonation. Class I shows the soft palate, fauces, uvula, and pillars. Class II shows the soft palate, fauces, and upper uvula. Class III shows the soft palate and base of uvula. Class IV shows only the hard palate. Sensitivity is approximately 60% and specificity 70% for difficult intubation — moderate predictive value when used alone, but best used in combination with other assessments.

| Mallampati Class | Structures Visible | Difficulty Prediction |
|---|---|---|
| I | Soft palate, fauces, uvula, pillars | Usually easy |
| II | Soft palate, fauces, upper uvula | Usually easy |
| III | Soft palate, base of uvula only | Possibly difficult |
| IV | Hard palate only | Likely difficult |

#### Thyromental Distance (TMD)

The distance from the thyroid notch to the mentum with the neck fully extended should be at least 6 cm (3 fingerbreadths). A distance below this suggests potentially difficult laryngoscopy because it reflects limited mandibular space available to displace the tongue during laryngoscopy.

#### Neck Mobility and Extension

Assessed at the atlanto-occipital joint, normal extension is 35 degrees. It is reduced in cervical spondylosis, ankylosing spondylitis, cervical spine precautions, and rheumatoid arthritis. The "sniffing position" alignment of oral, pharyngeal, and laryngeal axes requires adequate extension.

#### Mouth Opening

The inter-incisor distance (IID) should normally be 3 cm or more (2 fingerbreadths). Less than 3 cm may preclude standard laryngoscope blade insertion. Causes of limited opening include TMJ dysfunction, oral submucous fibrosis, scleroderma, post-radiation fibrosis, and infection (Ludwig angina).

#### Upper Lip Bite Test

In Class I, the lower incisors can bite above the upper lip vermillion border. In Class II, they can bite below the vermillion. In Class III, they cannot bite the upper lip at all. Class III predicts difficult intubation by assessing jaw protrusion (mandibular subluxation).

#### Other Predictors

A neck circumference above 40-43 cm is associated with difficult intubation (especially with OSA). BMI above 30 is associated with difficult mask ventilation. Prominent upper incisors, loose or missing teeth, dental prosthetics, a beard (which impairs mask seal), and a short thick neck with receding chin or high arched palate are all relevant.

### Composite Assessment

No single test is reliably predictive alone. Combining multiple factors improves predictive value. Various scoring systems attempt this, including the El-Ganzouri multivariate risk index, the Wilson risk score, and simplified scoring systems. The LEMON mnemonic for emergency airway assessment covers Look externally, Evaluate 3-3-2, Mallampati, Obstruction, and Neck mobility.

### Predictors of Difficult Mask Ventilation

The MOANS mnemonic covers Mask seal issues (beard, facial trauma), Obesity/Obstruction, Age over 55, No teeth (edentulous), and Stiff lungs (reduced compliance, COPD, asthma). The BONES mnemonic (Han criteria) covers Beard, Obese, No teeth, Elderly, and Snoring/OSA. The most dangerous situation is when difficult mask ventilation and difficult intubation occur together.

| Mnemonic | Target Prediction | Letters and Meaning |
|---|---|---|
| **LEMON** | Difficult intubation (emergency) | **L**ook externally, **E**valuate 3-3-2, **M**allampati, **O**bstruction, **N**eck mobility |
| **MOANS** | Difficult mask ventilation | **M**ask seal, **O**besity/Obstruction, **A**ge >55, **N**o teeth, **S**tiff lungs |
| **BONES** | Difficult mask ventilation (Han) | **B**eard, **O**bese, **N**o teeth, **E**lderly, **S**noring/OSA |
| **RODS** | Difficult SGA placement | **R**estricted mouth opening, **O**bstruction, **D**istorted anatomy, **S**tiff lungs |

### Difficult Supraglottic Airway Placement Predictors

The RODS mnemonic covers Restricted mouth opening, Obstruction (supraglottic pathology), Distorted anatomy, and Stiff lungs (high airway pressures).

## The ASA Difficult Airway Algorithm (2022 Update)

### Key Principles

Anticipation and preparation are paramount. Every plan should include a primary approach (Plan A) and backup plans (Plans B, C, D). Oxygenation should be continuously assessed throughout the algorithm. Help should be called early, and decision-making should be shared with the patient when possible, particularly regarding awake versus asleep approaches.

### Initial Decision: Awake Intubation vs. Intubation After Induction

Factors favoring awake intubation include anticipated difficult airway with predicted difficult mask ventilation and difficult intubation, known difficult airway from prior records, significant aspiration risk combined with a difficult airway, airway pathology that may worsen with induction, and a cooperative patient. Factors favoring intubation after induction include predicted easy mask ventilation even if intubation may be difficult, an uncooperative patient, urgency precluding an awake technique, and confidence that mask ventilation or an SGA will provide oxygenation backup.

### Algorithm Flow After Induction

#### Step 1: Initial Intubation Attempt

The first attempt uses direct or video laryngoscopy with optimization of positioning (sniffing position, ramping in obese patients), external laryngeal manipulation or BURP, and appropriate blade selection. Attempts should be limited: 3 attempts by one operator (some guidelines say 2), with a total of 3-4 attempts before declaring failure.

#### Step 2: Failed Intubation — Can Ventilate

When intubation fails but ventilation is possible, help should be called and oxygenation maintained via face mask or SGA. Alternative intubation approaches include video laryngoscopy (if not already used), SGA as a conduit for intubation (flexible bronchoscope through SGA), flexible bronchoscopic intubation, intubating LMA (Fastrach), lightwand, and retrograde intubation. If the case is non-emergent, waking the patient should be considered.

#### Step 3: Cannot Intubate, Cannot Oxygenate (CICO)

If ventilation remains impossible after SGA attempts, emergency invasive airway access is required. Cricothyrotomy using the scalpel-bougie-tube technique is preferred. Needle cricothyrotomy with jet ventilation has a higher complication rate. Surgical tracheostomy is typically too slow for an emergency.

### Extubation of the Difficult Airway

An extubation strategy should be formulated before extubating, with consideration of an airway exchange catheter and staged extubation in the ICU.

## Preparation for the Difficult Airway

### Equipment

Essential equipment includes multiple laryngoscope blades (Macintosh, Miller, various sizes), a video laryngoscope immediately available, supraglottic airways (multiple sizes, including an intubating LMA), a flexible bronchoscope, a bougie and stylets (standard and specialized), a cricothyrotomy kit (scalpel, bougie, 6.0 cuffed tube), jet ventilation equipment, and an end-tidal CO2 confirmation device.

### Human Factors

The airway plan should be discussed with the team preoperatively. Roles should be assigned for a CICO scenario. Cognitive aids (difficult airway algorithm posters, CICO checklists) should be used. A failed airway should be declared verbally and clearly to the entire team. Time awareness is critical: prolonged attempts without oxygenation cause harm.

<image>The ASA 2022 Difficult Airway Algorithm presented as a flowchart: starting with initial assessment and decision between awake intubation and intubation after induction. Branching pathways for successful intubation, failed intubation with adequate ventilation (alternative techniques listed), and the CICO emergency pathway leading to invasive airway access. Color coding: green for successful paths, yellow for backup options, red for the emergency CICO pathway. Key decision points are highlighted with diamond shapes.</image>

<image>A photographic-quality illustration showing the four Mallampati classes (I through IV) as viewed during oral examination: Class I showing full visualization of soft palate, uvula, and tonsillar pillars; Class II showing partial uvula; Class III showing only the base of uvula and soft palate; Class IV showing hard palate only. Each class labeled with its associated difficulty prediction and approximate incidence in the general population.</image>

<image>An anatomical diagram showing the alignment of the three axes during laryngoscopy: the oral axis (OA), pharyngeal axis (PA), and laryngeal axis (LA). Three panels demonstrate: (1) neutral head position with all three axes misaligned, (2) head elevation (flexion of lower cervical spine) partially aligning PA and LA, and (3) atlanto-occipital extension (sniffing position) aligning all three axes for optimal glottic visualization. Annotations show how neck pathology (cervical spondylosis, C-spine immobilization) limits this alignment.</image>

## Clinical Pearls

No single airway assessment tool is sufficiently sensitive or specific alone — always use a combination of assessments (Mallampati plus TMD plus mouth opening plus neck mobility plus body habitus). The most dangerous situation is not "cannot intubate" but "cannot intubate and cannot oxygenate," so predictors of difficult mask ventilation should always be assessed alongside intubation difficulty. Repeated laryngoscopy attempts cause bleeding and edema that progressively worsen conditions; the third attempt is usually worse than the first. Video laryngoscopy should be the first-line approach when difficulty is anticipated — there is no benefit to "trying direct first." The awake intubation is the safest approach when both difficult intubation and difficult rescue oxygenation are anticipated, and pressure to proceed should not override this judgment. A cricothyrotomy plan with immediately available equipment should always exist, because seconds matter in CICO. After a difficult airway encounter, thorough documentation and patient counseling are essential, including consideration of MedicAlert registration.

## References

- Apfelbaum JL, et al. 2022 American Society of Anesthesiologists practice guidelines for management of the difficult airway. *Anesthesiology*. 2022;136(1):31-81.
- Frerk C, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults. *Br J Anaesth*. 2015;115(6):827-848.
- Langeron O, et al. Prediction of difficult mask ventilation. *Anesthesiology*. 2000;92(5):1229-1236.
- Shiga T, et al. Predicting difficult intubation in apparently normal patients: a meta-analysis. *Anesthesiology*. 2005;103(2):429-437.
- Cook TM, et al. Major complications of airway management in the UK: results of the Fourth National Audit Project (NAP4). *Br J Anaesth*. 2011;106(5):617-631.