Airway Assessment

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OVERVIEW

The goal of airway assessment is to identify patients who may have difficult airways, mandating alternate approaches to airway management

“History predicts the future” – whenever possible identify:

1. the patient’s previous intubation grade and previous difficulties with airway management
2. determine what techniques and manoeuvres were required to optimize airway management conditions

Airway assessment and prediction of the difficult airway is an inexact science, particularly in the critically ill and in emergency situations

• In patients who have never been intubated, there is no method of prediction of difficult intubation that is both highly sensitive and highly specific
• Despite these caveats, airway assessment is valuable as it helps the airway practitioner develop the mindset of anticipating difficulties and planning appropriately

Always be prepared to manage an unanticipated difficult airway

THE DIFFICULT AIRWAY

There are various definitions of “the difficult airway”, with no definition universally accepted

• In general terms, an airway is considered difficult when oxygenation and ventilation cannot be achieved in the desired manner
• ‘The difficult airway’ represents a complex interaction between patient factors, the clinical setting, and the skills and preferences of the practitioner

American Society of Anaesthesiologists Task Force definitions:

The difficult airway is “the clinical situation in which a conventionally trained Anesthesiologist experiences difficulty with facemask ventilation, difficulty in supraglottic device ventilation, difficulty in tracheal intubation or all three”

• difficulty with facemask ventilation is the inability of an unassisted anesthesiologist:
  • a) to maintain oxygen saturation, measured by pulse oximetry,
    92%; or
  • b) to prevent or reverse signs of inadequate ventilation during positive-pressure mask ventilation under general anesthesia
• Difficult laryngoscopy occurs when “it s not possible to visualize 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”

Incidence

• incidence of difficult airways is poorly defined, and varies according to the setting
• incidence of failed intubation (Cook and MacDougall-Davis, 2012)
  • ~ 1 in 1–2000 in the elective setting
  • ~ 1 in 300 during rapid sequence intubation in the obstetric setting
  • ~ 1 in 50–100 in the emergency department (ED), intensive care unit (ICU), and pre-hospital settings

Difficult airway prediction is neither sensitive nor specific

• The difficult airway may be – to some extent – inherently unpredictable. In particular it is influenced by situational factors, including the clinical setting and the skills of the airway proceduralist
• A Danish study of ~188,000 intubations by anaesthetists in Denmark found that of the ~3100 difficult airways (3 or more intubation attempts), 93% were unanticipated. When the provider anticipated difficult airway, only about 25% actually ended up being difficult. The numbers for predicting difficult bag-value mask ventilation were similar.
• Additionally, airway assessment is often constrained in emergency situations and in critically ill patients
  • lack of patient cooperation and critical illness often prevents assessment
  • Levitan et al, 2004 found that in a series of 850 patients “Mallampati scoring, neck mobility testing, and measurement of thyromental distance could have been done in only one third of our non-cardiac arrest ED intubations and in none of the rapid sequence intubation failures”.

PRE-OPERATIVE AIRWAY ASSESSMENT

HISTORY

General

• Reason for airway management (e.g. surgery and approach)
• AMPLE history (allergies, medications, past medical history, last meal, events)
• exercise capacity
• smoker

Airway compromise

• Upper airway obstruction symptoms – stridor, hoarse voice, orthopnoea, drooling, dysphagia
• risk factors — suspected airway burn, neck trauma

Risk factors for difficult airway management, including

• Infections of oropharynx and neck
• Previous surgery or radiotherapy to neck
• Problems with mouth opening – e.g. trauma, soft tissue disorders, arthridities
• Problems with neck mobility – e.g. cervical spine disruption, rheumatoid arthritis, cervical fusion (e.g. operative, ankylosing spondylitis, scleroderma)
• obesity, OSA
• oropharyneal or neck masses
• difficult dentition
• pregnancy
• recent intubation (swelling, trauma)
• angioedema
• craniofacial syndromes
• Burns
• Airway trauma – blunt or penetrating
• Airway obstruction

Chart review

• previous anaesthetics and operations
• previous difficulties with mask ventilation or laryngoscopy
• Reason for intubation that can make intubation difficult – tumour, airway tumour or infection, trauma to neck/face, respiratory failure
• Previous intubation grade (Cormack & Lehane) and manoeuvres performed to improve view
• Difficulty with bag-mask ventilation

EXAMINATION

General

• Level of consciousness + co-operation
• BMI

Face

• Beard
• craniofacial deformity

Mouth

• Mallampati grade I to IV
• Mouth opening — Inter-incisor distance (> 3cm = good, < 3cm = bad)
• Shape of palate
• Jaw protrusion

Teeth

• Edentuous
• Teeth prominence (upper incisors) and condition
• Relation of maxillary to mandibular incisors during normal jaw closure
• dentures/ caps/ crowns/ loose teeth

Neck

• Range of motion of head and neck
• thyro-mental distance <6cm
• Neck length and circumference/ thickness
• Compliance of mandibular space
• Sternomental distance

INVESTIGATIONS

• Nasal endoscopy
• Awake laryngoscopy
• Lateral neck xray
• CXR
• CT neck
• MRI neck

MALLAMPATI SCORE

Modified Mallampati Score

• Class I: Soft palate, uvula, fauces, pillars visible
• Class II: Soft palate, uvula, fauces visible
• Class III: Soft palate, base of uvula visible
• Class IV: Only hard palate visible

Other information

• insufficiently accurate to be used alone
• Class III/IV predicts difficult intubation, but only about 5% are actually difficult
• often infeasible in ED patients
• scoring varies depending on:
  • whether the patient phonates or whether the tongue is maximally protruded (improves the grade)
  • lies supine versus upright (worsens the grade)

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 3: Only epiglottis seen, none of glottis seen
• Grade 4: Neither glottis nor epiglottis seen

Intubation is likely to be difficult with a Grade 2b view or worse

THE 6D METHOD

As described by Rich, 2005; see this table.

USEFUL 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 LMA = RODS

• Restricted mouth opening
• Obstruction
• Distorted airway
• Stiff lungs or c-spine

Difficult surgical airway = SHORT

• Surgery
• Hematoma
• Obesity
• Radiation distortion or other deformity
• Tumor

References and Links

LITFL

• CCC — Difficult airway algorithms

Journal articles

• American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway. Anesthesiology. 2003 May;98(5):1269-77. Erratum in: Anesthesiology. 2004 Aug;101(2):565. PMID: 12717151. [Full Text]
• Bair AE, Caravelli R, Tyler K, Laurin EG. Feasibility of the preoperative Mallampati airway assessment in emergency department patients. J Emerg Med. 2010 Jun;38(5):677-80. doi: 10.1016/j.jemermed.2008.12.019. PMID: 19297115.
• Cook TM, MacDougall-Davis SR. Complications and failure of airway management. Br J Anaesth. 2012 Dec;109 Suppl 1:i68-i85. doi: 10.1093/bja/aes393. PMID: 23242753. [Free Full Text]
• Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia. 1984 Nov;39(11):1105-11. PMID: 6507827.
• Greenland KB. Airway assessment based on a three column model of direct laryngoscopy. Anaesth Intensive Care. 2010 Jan;38(1):14-9. PMID: 20191771.
• Mallampati SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, Liu PL. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J. 1985 Jul;32(4):429-34. PubMed PMID: 4027773.
• Nørskov AK, Rosenstock CV, Wetterslev J, Astrup G, Afshari A, Lundstrøm LH. Diagnostic accuracy of anaesthesiologists’ prediction of difficult airway management in daily clinical practice: a cohort study of 188 064 patients registered in the Danish Anaesthesia Database. Anaesthesia. 2015 Mar;70(3):272-81.PMID: 25511370.
• Rich JM. Recognition and management of the difficult airway with special emphasis on the intubating LMA-Fastrach/whistle technique: a brief review with case reports. Proc (Bayl Univ Med Cent). 2005 Jul;18(3):220-7. PMC1200729.
• Yentis SM, Lee DJ. Evaluation of an improved scoring system for the grading of direct laryngoscopy. Anaesthesia. 1998 Nov;53(11):1041-4. PMID: 10023271.
• Yentis SM. Predicting difficult intubation – worthwhile exercise or pointless ritual? Anaesthesia. 2002 Feb;57(2):105-9. PMID: 11871945.

FOAM and web resources

• Emergency Management of Anaesthetic Crises — Airway emergencies
• Resus.ME — Difficult airways can’t be reliably predicted (2014)
• Resus.ME — Mallampati assessment in ED airways (2014)

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