Examination and Evaluation of the Airway

Why examine and evaluate a patient's airway preoperatively?

1. Determine ease or difficulty of airway manipulation (intubation, mask ventilation)

2. To prepare the anesthetist

→ Selection of airway devices, techniques, and procedures

3. Minimize harm during subsequent airway management

4. Determine airway-related risks in order to

→ Discuss them with patients

→ Avoid risk-related problems

What are the three main mechanisms of injury that account for most serious airway complications?

1. Esophageal intubation

2. Failure to ventilate

3. Difficult intubation

Which airway issue can contribute to esophageal intubation, failure to ventilate, and other complications?

Difficult intubation

What is the key to anticipating difficult intubation in most cases?

Performing a thorough airway evaluation in advance

True or False: Most difficult intubations occur without warning and cannot be predicted

False

→ 98% or more can be anticipated with proper airway evaluation

Why is airway evaluation important for anesthetists?

It helps determine the anticipated ease or difficulty of airway management techniques

Types of airway management techniques

1. Bag-mask ventilation

2. Direct laryngoscopy (for tracheal intubation)

3. Blind airway techniques

4. Fiberoptic bronchoscopy

5. Cricothyrotomy/cricothyroidotomy

6. Tracheostomy

What are examples of blind airway techniques?

LMA and Combitube

What key questions should you ask a patient during airway evaluation?

History

→ Any problems with intubation before?

→ Have you been told you have a difficult airway?

Mouth

→ Any crowns, loose, chipped, or removable teeth

→ OSA, snore, or smoke

→ Anything removable in the mouth?

Conditions

→ Acid reflux or GERD

→ Diabetes

→ Clotting abnormalities

→ Congenital syndromes and abnormalities

Neck

→ Neck radiation

→ Arthritis

→ Circumference

Which types of joint issues can affect airway management?

1. TMJ disease → Limits mouth opening

2. Ankylosing spondylitis → Restricts neck and spine movement

3. Rheumatoid arthritis (RA)

4. Osteoarthritis (OA)

Clotting abnormalities should be asked about prior to what airway intervention?

Nasal airway

What two things should be evaluated separately based on history, examination, and diagnostic tests?

1. Ability to ventilate

2. Ability to intubate

What should you confirm before giving muscle relaxants during airway management?

Make sure you can intubate

What body position should the patient tolerate for a normal airway?

Ability to lie supine

What part of a patient's history is most reassuring for predicting easy intubation?

Past history of easy intubation

What mouth opening measurement suggests a normal airway?

Three finger-breadths

≥ 3-4 cm

What Mallampati class is associated with a normal airway?

Class I or II

What thyromental distance suggests a normal airway?

Three finger-breadths

→ From chin to thyroid notch with neck fully extended

→ Greater than 6 cm

What neck features suggest a normal airway?

→ Full range of motion

→ Slender neck without masses

What is the normal extension angle of the atlanto-occipital joint for airway assessment?

35 degrees

What are the airway assessment risk features for difficult intubation related to:

1. Mouth opening

2. Thyromental distance

3. Mallampati score

4. Neck movement

5. Mandible movement

6. Neck anatomy

7. Past intubation history

BE ABLE TO DISTINGUISH SIGNS OF DIFFICULT MASK VENTILATION FROM SIGNS OF DIFFICULT INTUBATION

1. < 4 cm

2. < 6 cm

3. Class III or IV

4. < 80% range of motion

5. Inability to advance mandible (poor prognathism)

6. Obese or thick neck

7. Positive history of difficult intubation

What percentage of the general adult population has difficult mask ventilation (DMV)?

5%

What are the main goals of face-mask ventilation?

1. Maintain airway patency

2. Oxygenation

How is difficult mask ventilation (DMV) defined?

Inability of an unassisted anesthesiologist to:

1. Keep SpO₂ > 92%

2. Prevent or reverse signs of inadequate ventilation during positive pressure mask ventilation under GA

Predictors of difficult mask/bag mask ventilation

BE ABLE TO DISTINGUISH SIGNS OF DIFFICULT MASK VENTILATION FROM SIGNS OF DIFFICULT INTUBATION

OBESE

1. Obese → BMI > 30

2. Beard

3. Elderly → > 57

4. Snores/OSA

5. Edentulous

In addition:

→ Mallampati class III or IV

→ Severely limited mandibular protrusion

→ Neck radiation

What condition can make mask ventilation severely difficult due to stiff tissues and limited mobility?

Neck radiation

Acronym used for airway evaluation

MOUTHS

M → Mandible: length and ability to sublux

O → Opening: measure mouth opening

U → Uvula: check visibility (Mallampati)

T → Teeth: check for loose, chipped, or cracked teeth

H → Head: assess neck flexion, extension, and rotation

S → Silhouette: look for upper body issues like kyphosis or large breasts

What mandibular issues can make direct laryngoscopy difficult?

1. Temporomandibular diseases like arthritis

2. Mandibular hypoplasia (small chin)

3. Overjet and overbite

4. Maxilla/mandible prognathism

5. Mandible retrognathism

What airway challenges can acromegaly cause?

1. Difficult laryngoscopy (DL)

2. Difficult mask ventilation (DMV)

3. Difficult intubation (DI)

Why is acromegaly associated with difficult DMV, DL, and DI?

1. TMJ arthritis

→ Limited range of motion

2. Small mouth opening

3. Large nose and tongue

4. Thick mandible

5. Overgrowth of soft tissues

→ Pharynx, larynx, and vocal cords

6. Central apnea or OSA

What congenital issues can make direct laryngoscopy difficult?

1. Torus palatinus

2. Cleft palate

3. Cleft lip

4. Micrognathia

What congenital abnormalities are most common in pediatrics?

Cleft palate and cleft lip

What should you check for when inspecting the lips during airway evaluation?

1. Chapped skin

2. Open sores

3. Scars

4. Abrasion

Why is poor dentition a concern during airway management?

Loose or damaged teeth can fall out, get lodged in the airway or bronchial tree, and lead to complications like abscess formation

Upper lip bite test is a modification of

Mandibular protrusion test

What finding on the upper lip bite test predicts a likely adequate laryngoscopic view?

The lower teeth can bite the upper lip at or above the vermilion border

What joint movement does the upper lip bite test help assess?

TMJ glide

What does a mouth opening < 3 cm suggest?

TMJ dysfunction

What does a mouth opening < 2.5 cm indicate?

May preclude normal direct laryngoscopy

What does a mouth opening < 2 cm indicate?

Limits laryngoscopic equipment

When mouth opening is limited, what should you rule out?

Pain vs mechanical cause

What are two main reasons for limited mouth opening at the TMJ?

Pain limitation and mechanical limitation

What should you assess when palpating the TMJ?

1. Movement

2. Pain

3. Crepitus

4. Clicking

What neck range of motion is considered normal for airway assessment?

More than 90° of flexion and extension

What does neck mobility < 80° indicate?

Triples the risk of a poor laryngoscopic view

To obtain a direct line of sight during intubation, the patient is positioned in the __________, which involves flexing the __________ and extending at the __________

1. Sniffing position

2. Lower cervical spine (flexing)

3. Atlanto-occipital joint (extending)

Why can't patients in a cervical collar be placed in the sniffing position?

Because the collar restricts neck flexion and extension

What is used to estimate the atlanto-occipital gap during airway assessment?

Upper-lower dental angle

What is the normal angle for the atlanto-occipital gap?

≥ 35°

Why is the atlanto-occipital gap important for direct laryngoscopy?

Reduced angle = Improper axial alignment

→ DL more difficult

What physical sign in diabetics may indicate limited joint mobility?

Prayer sign (interphalangeal joint gap)

What does a positive prayer sign indicate in airway evaluation?

Limited joint mobility

→ Can also affect the cervical spine, TMJ, and larynx

How much more likely are long-term type 1 diabetics to have intubation difficulty?

10 times more likely

What is the gold standard for oropharyngeal examination (OPE)?

Mallampati classification

What is the Mallampati classification based on?

Structures seen with maximal mouth opening and tongue protrusion

→ Without phonation

Mallampati classes

I: Soft palate, fauces, uvula, tonsillar pillars

II: Soft palate, fauces, and uvula

III: Soft palate and base of the uvula

IV: Only the hard palate is visible

What does a false positive mean in Mallampati Class IV?

The airway looks difficult on exam, but intubation ends up being easy

Cormack-Lehane classification

Grade I: Full view of the glottis

Grade II: Only the posterior commissure is visible, partial view of the glottis

Grade III: Only the epiglottis is seen

Grade IV: No epiglottis or glottic structure visible, only soft palate

True or false: One indicator by itself does not predict difficult airway

True

Three minimum requirements for successful direct laryngoscopy (DL)

1. The mouth must open (at least a little)

2. The three axes — oral, pharyngeal, and tracheal — must be at least somewhat aligned in the sniffing position

3. There must be space to displace the tongue and see the glottis

The amount of the _________ you can visualize correlates with the difficulty of intubation

Posterior pharynx

What anatomical feature can obscure the view of the pharynx and larynx during intubation?

A large tongue relative to the size of the mouth

A relatively large tongue that limits pharyngeal and laryngeal visualization is a common airway challenge in which condition?

Down syndrome

What are five predictive risk factors for difficult direct laryngoscopy?

1. Limited jaw movement

2. Poor head and neck movement

3. Receding chin (small mandible)

4. Buck teeth (prominent maxillary incisors)

5. Obesity

Which commonly cited risk factor for difficult laryngoscopy is not considered an independent predictor?

Obesity