Airway assessment

 

List:

·        Theories

·        Approach

·        Tests

·        Syndromes

 

Theories:

Three axis theory

·      Oral

·      Pharyngeal

·      Laryngeal

Two column theory

·      Posterior-facing curve from mouth to pharynx

o  Flattened by extension of head

·      Anterior-facing curve from pharynx to larynx

o  Flattened by flexion of lower C spine

·      Point of inflection at base of epiglottis

 

Approach to assessment:

Will procedures be hard?

Red flags:

·      Airway infection

·      Airway cancer

·      Airway trauma

·      Airway radiation

·      Congenital abnormality

·      Previous difficult airway

Bag-mask ventilation:

·      Elderly

·      No teeth

·      Beard

·      ↓Jaw protraction

·      Obese

·      OSA (i.e. STOPBANG)

LMA insertion:

·      Small mouth

LMA ventilation:

·      Obese

·      Stiff neck

·      Stiff lungs

·      Abnormal upper airway

Laryngoscopy/intubation:

·      ↑MP

·      ↓TMD, TMH

·      ↓IID

·      ↓Neck ROM

·      Obesity

·      OSA (i.e. STOPBANG)

AFOI:

·      Abnormal anatomy

·      Obesity

·      Co-operation

FONA:

·      Obesity

·      Abnormal anatomy

Extubation:

·      Difficulty with intubation

·      Narcotic concentration

·      Airway swelling

What are the stakes?

·      Does surgery interfere with the airway?

·      What is the aspiration risk?

·      What is the patient’s cardioresp reserve?

 

Airway tests:

 

Difficult laryngoscopy:

 

Sensitivity

Specificity

Mallampatti

50%

80%

Thyromental distance (6cm)

37%

89%

Mouth opening (<3cm)

22%

94%

Upper lip bite

67%

92%

Thyromental height

83%

99%

(Cochrane review 2018 and Anesth Analg 2013)

 

Commentary:

Utility

·      Specificities (“Will this be an easy airway?”) are high

o   No one cares

·      Sensitivities (“Will this be a difficult airway?”) are low

o   Everyone cares

·      Low prevalence = negative predictive value is high regardless

o   Why bother

Relevance

·      Anatomically normal airways:

o   No room in the mouth = nasal fibreoptic

o   Anterior larynx = hyperangulated blade

·      Anatomically abnormal airways: there are no useful tests

o   i.e. trauma, infection, cancer, radiation, congenital

Upshot

·      Important to retrieve past anaesthesia notes

·      Important to make plan ABCD for every single anaesthetic

o   Less obvious alternative: check all equipment out loud

 

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