Airway Assessment

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Definition

  • The purpose of an airway assessment is to predict and plan for a difficult airway
  • The definition of a difficult airway1 is: “the clinical situation in which a conventionally trained Anaesthesiologist experiences difficulty with facemask ventilation, difficulty in supraglottic device ventilation, difficulty in tracheal intubation or all three” where:
    • Difficulty with facemask ventilation is the inability of an unassisted anaesthesiologist:
      1. to maintain oxygen saturation, measured by pulse oximetry, 92%; or
      2. to prevent or reverse signs of inadequate ventilation during positive-pressure mask ventilation under general anaesthesia
    • Difficult laryngoscopy occurs when “it’s not possible to visualise any portion of the vocal cords with conventional laryngoscopy”
      • This typically corresponds to a Cormack and Lehane Grade IV laryngoscopy view
    • Difficult endotracheal intubation occurs when “proper insertion of the tracheal tube with conventional laryngoscopy requires more than three attempts or more than 10 minutes”

Pre-Operative Airway Assessment

LEMON Screening Tool to Predict Difficult Laryngoscopy

  • Look:
    • Dose the patient look like the stereotypical difficult intubation
  • Evaluate: 3:3:2 rule:
    • 3 fingers width of mouth opening
    • 3 fingers width of thyromental distance (from the thyroid cartilage to the mental process of the mandible)
    • 2 fingers width of distance from the hyoid to the thyroid
  • Mallampati score
  • Obesity and obstruction
    • Is the patient morbidly obese
    • Is there some sort of obstruction (e.g. abscess)
  • Neck mobility

BONES to Predict Difficult Bag Valve Mask Ventilation

  • Beard
  • Obesity
  • No teeth
  • Sleep apnoea or Snoring

Although the most valuable independent predictors of difficult mask ventilation as per RCoA analysis are: Age > 55 years, BMI > 26, lack of definition, facial hair, history of snoring. Alternatively MOANS can be used instead — mask seal features (e.g. beards, saliva or blood or anatomical features such as facial fractures or retrognathia), obesity, age > 55 years, no teeth, snoring or stiff

RODS to Predict Difficult Laryngeal Mask Airway Insertion

  • Restricted mouth opening
  • Obstruction; airway obstruction at or below the level of the glottis will not be relieved by the insertion of a supraglottic device
  • Distorted airway: unusual airway anatomy may prevent the supraglottic device from seating properly
  • Stiff lungs or c-spine/neck: decreased lung compliance (e.g. asthma) may make ventilation with a supraglottic device impossible and in patients with limited neck movement, the supraglottic device may form a poor seal

SHORT to Predict Difficult Surgical Airway

  • Surgery of the neck
  • Haematoma at the neck
  • Obesity at the neck
  • Radiation distortion or other deformity
  • Tumour

The ANZCA document outlines the essential components of the routine airway assessment:

  1. Presence of any previous anaesthesia issues
  2. Presence of any gastric reflux
  3. Presence of any obstructive sleep apnoea
  4. Body mass index
  5. Mouth opening
  6. Modified Mallampati score
  7. Dental status
  8. Thyro-mental distance
  9. Jaw protrusion
  10. Cervical spine movemen

History

  • General history elements:
    • Reason for airway protection/management
    • AMPLE history (allergies, medications, past medical history, last meal, events)
    • Exercise capacity
    • Smoker
  • Symptoms or risk factors for airway compromise:
    • Stridor, hoarse voice, orthopnoea, drooling, dysphagia
    • Risk factors - suspecterd airway burn, neck trauma, goitre
  • Risk factors for difficult airway management: infections of oropharynx and neck (e.g. Ludwig’s angina), problems with mouth opening (e.g. trauma, soft tissue disorders), problems with neck mobility (e.g. cervical spine disruption, rheumatoid arthritis, cervical fusion), , Obesity, OSA, oropharyngeal or neck masses, dentition, pregnancy, recent intubation, angioedema, burns

Chart Review

  • Whenever possible identify:
    • The patient’s previous intubation grade and previous difficulties with airway management
    • Determine what techniques and manoeuvres were required to optimise airway management conditions
    • History of airway-altering changes since the last anaesthetic (e.g. significant weight gain, C-spine surgery, head and neck radiotherapy etc.)

Examination

  • General
    • Level of consciousness and co-operation
    • Level of comfort (i.e. can the patient be positioned properly, or are they too short of breath)
    • BMI
    • Pregnancy
  • Face: facial hair, craniofacial deformities
  • Mouth
    • Mallampati grade (>2 predicts difficult airway)
    • Mouth opening (inter incisor distance)
    • Shape of palate (e.g. arched or narrow)
    • Jaw protrusion and patient’s ability to prognath (voluntarily protrude the mandible)
  • Teeth
    • Teeth prominence
    • Relaxation of maxillary to mandibular incisors during normal jaw closure
    • Dentures/caps/grows/loose teeth
  • Neck
    • Range of motion of head and neck
    • Thyro-mental distance <6cm
    • Mandibulo-hyoid distance <4cm
    • Sternomental distance <12cm
    • Neck length and circumference/thickness
    • Compliance of mandibular space

Investigations

  • Investigations to consider:
    • Neck ultrasound
    • Nasal endoscopy
    • Awake laryngoscopy
    • Lateral neck x-ray
    • Chest X-ray
    • CT/MRI neck
  • Mallampati score
    • Class I: Soft palate, uvula and faucial pillars visible
    • Class II: Soft palate and faucial pillars visible with the uvula partially obscured by tongue
    • Class III: Soft palate and base of uvula visible
    • Class IV: Only hard palate visible

  • Cormack-Lehane Classification
    • Grade 1: Full view of glottis
    • Grade 2a: Partial view of glottis
    • Grade 2b: Only posterior extremity of glottis seen or only arytenoid cartilages
    • Grade 3a: Epiglottis can be lifted from the posterior pharyngeal wall
    • Grade 3b: Epiglottis cannot be lifted from the posterior pharyngeal wall
    • Grade 4: Neither glottis nor epiglottis seen

  • Percentage of visible glottic opening (POGO)
    • It requires the observer to estimate how much of the glottis is not visualised

Mnemonics

  • Difficult intubation = LEMON
    • Look externally
    • Evaluate 3-3-2 rule
    • Mallampati score
    • Obstruction
    • Neck Mobility
  • Difficult BVM = BONES
    • Beard
    • Obese
    • No teeth
    • Elderly
    • Sleep Apnea / Snoring
  • Difficult surgical airway = SHORT
    • Surgery
    • Hematoma
    • Obesity
    • Radiation distortion or other deformity
    • Tumor

Other Notes

The ANZCA document outlining airway assessment describes it being mandatory to provide written information to the patient and their medical practitioner when a difficult airway is encountered as well as advice for them to get a medical alert bracelet.

Determining an Airway Management Plan

There are nine core airway management considerations:

  1. Is there information about any previous airway difficulties?
  2. Is there any altered cardiorespiratory physiology?
  3. What is the impact of the surgery on the airway?
  4. How difficult will it be to bag-and mask ventilate?
  5. How difficult is it to place a supraglottic airway?
  6. How difficult will it be to intubate the patient?
  7. How difficult will it be to perform an infraglottic airway?
  8. What is the risk of aspiration?
  9. How easy will they be to extubate safely?

Sources

Footnotes

  1. More on the definition of the anatomically difficult airway can be read at Recognition of the anatomically difficult airway ↩

Disclaimer: These notes are for educational purposes only and are not medical advice. I do not claim copyright for the content or images unless otherwise stated. For concerns or changes, create a new issue on GitHub.

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