Airway assessment

Identifying the “difficult to intubate patient”

* Long incisors / Overriding upper teeth
* Poor TMJ function / mouth opening < 3cm
* Mallampatti 3 or 4
* Small jaw
* Narrow palate
* Thryomental distance < 6 cm
* Rigid submandibular space from infection or tumour
* Impaired mobility of cervical spine

Identifying the patient likely to be difficult to mask ventilate

* Elderly
* Edentulous
* Obese
* Snorers / Sleep apnoea
* Bearded
* Patients with airway obstruction (stridor)

Pathologic Causes of a Difficult Airway

* Congenital and surgically induced facial and upper airway deformities
* Maxillofacial and airway trauma including oedema
* Airway tumours, abscesses and haematomas
* Cervical trauma
* Fibrosis of face and neck

Anatomical Causes of Difficult Airway

* Relative tongue/pharyngeal size
* Mallampati classification
* Extent of mandibular opening
* Mandibular space
* Thyromental distance
* Horizontal length of mandible
* Atlanto-occipital joint extension

Relative tongue/pharyngeal size

* Degree of visibility of oropharyngeal structures including extent of mandibular opening ie. Mallampati classification
* Best performed with patient sitting, head in extension, tongue out
* Correlates with laryngoscopic view:
Class 1= Grade 1 view 99-100% of the time
Class 4= Grade 3 or 4 view 100% of the time

Mallampati classification

* Class 1- soft palate, fauces, uvula, anterior and posterior pillars visible
* Class 2- soft palate, fauces uvula visible
* Class 3- soft palate, base of uvula visible
* Class 4- soft palate not visible

Mandibular Space

* Space anterior to the larynx determines how easily the laryngeal axis will fall in line with the pharyngeal axis when the atlanto-occipital joint is extended.
* If the thyromental distance is very short, the laryngeal axis will make a more acute angle with the pharyngeal axis and it will be more difficult for atlanto-occipital extension to bring these 2 axes into line.

Thyromental distance

* Distance should be measured from inside of mentum to thryoid cartilage.
* A thyromental distance of > 6 cm and a horizontal length of mandible of > 9 cm strongly suggest that direct laryngoscopy will be relatively easy

Atlanto-occipital joint extension

* When the neck is flexed on the chest (25-35°) and the atlanto-occipital joint is well extended head extended on the neck, the pharyngeal and laryngeal axes are brought more closely into a straight line-sniff position.
* When the atlanto-occipital joint cannot be extended, attempts to do so cause the convexity of the cervical spine to bulge anteriorly, pushing the larynx more anterior.