Quick airway assessment

1.  Ask the patient to open their mouth wide then protrude their tongue: can assess Mallampati Score and TMJ  movement

 

2.  Neck Circumference

 

3.  Dentition: can assess incisional measurement and presence of any chipped or loose teeth

 

4.  Neck Range of Motion 

 

 

Thorough Airway assessment:

1. History : Medical, surgical and/or anesthetic factors

Anesthetic factors which could predispose to a difficult airway are:

     Edema                             Burns

     Bleeding                         Tracheal/oesophageal stenosis

     Perforation                      Pneumothorax

     Aspiration                       Tracheal compression

 

I I . General, physical and regional examination :

 

i. Patency of nares

 

ii. Mouth opening of at least 2 large finger breadths between upper and lower incisors in adults is desirable.

 

iii. Teeth: Prominent upper incisors or canines can impose a limitation on alignment of the oral/pharyngeal axes during laryngoscopy, especially with a large tongue. They can compound the difficulty during the direct laryngoscopy or bag-mask ventilation. An edentulous state, on the other hand, can render axis alignment easier but hypopharyngeal obstruction by the tongue can occur.

 

iv. Palate: A high arched palate or long, narrow mouth may present difficulty.

 

v. Assess Prognathism

 

vi. Temporo-mandibular joint movement: may be restricted by ankylosis/fibrosis, tumors, etc.

 

vii. Measurement of submental space: hyomental/thyromental length should ideally be greater than  6 cm/3 large finger breadths.

 

viii. Patient's neck : A short, thick neck is often associated with a difficult intubation. Any masses in the neck, extension of the neck, neck mobility or lack there of,  and ability to assume ‘sniffing’ position should be  thoroughly assessed.

 

ix. Any systemic or congenital disease requiring special attention during airway management (e.g. respiratory failure, significant coronary artery

disease, acromegaly, etc.).

 

x. Physiologic conditions: Pregnancy and obesity.

 

III. Specific tests for assessment

A. Anatomical criteria

1. Mallampatti test:

The Mallampati classification correlates tongue size to pharyngeal size. This test is performed with the patient in the sitting position, head in a neutral position, mouth wide open and the tongue protruding to its maximum. Patient should not be asked to say "awe" as it can result in a false elevation of the soft palate.

Classification is assigned, according to the extent the base of the tongue is able to mask the visibility of pharyngeal structures, into four classes: 

Class I : Visualization of the soft palate, fauces; uvula, anterior and the posterior pillars.

Class II : Visualization of the soft palate, fauces and uvula.

Class III : Visualization of soft palate and base of uvula.

Class IV: Only hard palate is visible. Soft palate is not visible at all.

 

 

2. Atlanto occipital joint (A-O) extension:

Assesses the ability to make a "sniffing" position for intubation (alignment of oral, pharyngeal and laryngeal axes). The patient is asked to hold their head erect, facing directly to the front, then is asked to extend the head maximally, and the examiner estimates the angle traversed by the occlusal surface of upper teeth. Measurement can be by simple visual estimate or more accurately with a goniometer. Any reduction in extension is expressed in grades:

Grade I : >35°

Grade II : 22°-34°

Grade III : 12°-21°

Grade IV : < 12°

Normal angle of extension is 35° or more.

 

 

3. Mandibular space

i . Thyromental distance:

The distance from the mentum to the thyroid notch while the patient’s neck is fully extended.  This measurement helps in determining how readily the laryngeal axis will fall in line with the pharyngeal axis when the A-O joint is extended. 

Alignment of these two axes is difficult if the thyromental distance is < 3 finger breadths or < 6 cm in adults; 6-6.5 cm is less difficult, while > 6.5 cm is normal.

 

i i . Sterno-mental distance:

The distance from the suprasternal notch to the mentum. It was measured with the head fully extended on the neck with the mouth closed. A value of less than 12 cm is found to predict a difficult intubation.

 

i i i . Mandibulo-hyoid distance:

Measurement of mandibular length from chin (mental) to hyoid should be at least 4 cm or three finger breadths. It was found that laryngoscopy became more difficult as the vertical distance between the mandible and hyoid bone increased.

 

iv. Inter-incisor distance:

It is the distance between the upper and lower incisors.  Normal is approximately 5 cm.  Less than 3cm can assist in predicting a difficult laryngoscopy and less than 2 cm can assist in predicting a difficult LMA insertion.

 

 

B. Direct laryngoscopy and fibreoptic bronchoscopy

Difficulty in intubation can be classified according to the view obtained during direct laryngoscopy into 4 grades. These 4 grades of laryngoscopic views were definedby Cormack and Lehane in 1984.

Grade I – Visualization of entire laryngeal aperture.

Grade II – Visualization of only posterior commissure of laryngeal aperture.

Grade III – Visualization of only epiglottis.

Grade IV  – Visualization of just the soft palate.

Grade III and IV predict difficult intubation.

An optimal position for alignment of axes of mouth, pharynx and larynx achieved by flexion of neck and extension of the head at the A-O joint is very important.

 

C. Radiographic assessment

1. From skeletal films

Lateral c-spine x-ray film of the patients with their head in a neutral position is required for the following measurement:

i . Mandibulo-hyoid distance:

i i . Atlanto-occipital gap:

i i i . Relation of mandibular angle and hyoid bone

iv. Anterior/Posterior depth of the mandible :

v. C1-C2 gap

 

2. Fluoroscopy for dynamic imaging (cord mobility, airway malacia, and emphysema).

 

3. Oesophagogram (inflammation, foreign body, extensive mass or vascular ring).

 

4. Ultrasonography (assessment of anterior mediastinal mass, lymphadenopathy, differentiates cyst from mass and cellulitis from abscess).

 

5. CT/MRI (congenital anamolies, vascular airway compression).

 

6. Video-optical intubation stylets (combines viewing capability with the familiar handling of intubation devices).

 

 

D. Indicators of difficult intubation

The classic signs altering the operator to difficulty of intubation may be summarised as follows:

a. Poor flexion–extension mobility of the head and neck.

 

b. A receding mandible and presence of prominent teeth.

 

c. A reduced A-O distance and a reduced space between C1 and the occiput.

 

d. Large tongue size – related more to the ratio of the anterior length of the tongue to the length of the chin or mandible.