In this article Dr Ravi Bhagrath, Consultant Anaesthetist at Bart’s Health NHS Trust and co-author of the Difficult Airway Society (DAS) 2015 guidelines for management of unanticipated difficult intubation in adults, outlines how to perform a comprehensive airway assessment, the basis of every airway management plan.
Airway assessment is the cornerstone of good airway management. An airway evaluation should be carried out in all patients requiring sedation, anaesthesia, airway support or intervention. The 4th National Audit Project (NAP4) found that up to a quarter of patients had no recorded pre-operative airway assessment. Serious adverse events occurred even when no problem with airway management had been anticipated, emphasising the need for vigilance and a prepared airway strategy.
An airway strategy is a series of plans which can be adapted according to the clinical scenario, it provides a structured approach for dealing with difficulty should it arise. The strategy should be in place before induction of anaesthesia and discussed at the team brief and sign-in stage of the WHO Surgical Safety Checklist .
Airway assessment aims to predict if the patient’s anatomy might make bag-mask ventilation (BMV), supraglottic airway device (SAD) placement or intubation challenging or impossible. A good pre-operative assessment reduces the likelihood of an unanticipated difficult intubation and associated complications.
There are a number of different beside tests for assessing the airway but no single test is completely reliable   . Airway assessment should include history, examination and relevant investigations. If you think the airway may be difficult to manage, pause and consider if the procedure could be done under a local or regional anaesthetic techniques or to secure the airway with an awake tracheal intubation.
Key elements in the history
- Current symptoms including shortness of breath (dyspnoea), difficulty swallowing (dysphagia) and difficulty speaking (dysphonia)
- Symptoms of obstructive sleep apnoea (OSA). This will be discussed in more details as part of the activity on Airway Management in the Obese Patient, in Week 5
- Previous surgery or radiotherapy to the head, neck and mediastinum
- Review of any previous anaesthetic charts for indications of difficulty and which devices or techniques were used
- Whether the patient has been told they have a difficult airway or given a difficult airway alert card or form, such as the DAS Airway Alert Form
- Chronic medical problems that can make the airway more challenging including diabetes mellitus, ankylosing spondylitis and rheumatoid arthritis
A brief airway examination should include a general assessment of the patients body habitus, Mallampati score (see below), a test of neck extension and ability to protrude the lower jaw.
Other things to consider are:
- Is the patient obese, do they have a short neck or increased neck circumference?
- Do they have a beard? A beard can make bag mask ventilation difficult as it prevents a good seal between facemask and skin, it may also mask a small lower jaw
- Face and neck scarring: burns or contractures can reduce mouth opening and ease of face mask ventilation and indicate anatomical distortion
- Dental condition: prominent incisors, mobile teeth, and gaps between the teeth can cause difficulty
- Jaw subluxation is useful to determine temporomandibular joint mobility: you can test this by asking the patient to bite their upper lip
- Neck movement: most importantly, atlanto-occipital extension. You can test this by placing a finger at the back of the patient’s neck and asking them to look up at the ceiling
- Radiotherapy: previous head and or neck radiotherapy can result in permanent soft tissue damage, the tissues become hard and fixed or ‘woody’. This can make simple airway manoeuvres difficult or impossible
Appearance of neck after radiotherapy
Modified Mallampati scores
Class 1. Soft palate, fauces, uvula and pillars seen
Class 2. Soft palate, fauces and uvula seen
Class 3. Soft palate and base of the uvula seen
Class 4. Soft palate not visible at all
Classes 3 and 4 are associated with increasing difficulty in intubation.
Measurement of distances
A thyromental distance of <7cm and a sternomental distance of <12.5cm are suggestive of potential airway management difficulty.
A gap of at least 2cm between the upper and lower incisors, is required to insert a blade for direct or videolaryngoscopy.
Finally, palpation of the front of the neck is important to assess the position of the trachea, the presence of any masses (e.g. thyroid, lymph nodes), the cricothyroid membrane and evidence of previous surgery.
The use of the ‘laryngeal handshake’, as described by Levitan , promotes confidence in the recognition of the three dimensional anatomy of the laryngeal structures we covered in Week 1. The laryngeal handshake is performed with the non-dominant hand, identifying the hyoid bone and thyroid cartilage, stabilizing the larynx between thumb and middle finger and moving down the neck to palpate the cricothyroid membrane with the index finger.
Flexible nasendoscopy: FNE is a useful, simple technique for assessing the nasopharyngeal and oropharyngeal spaces. This is commonly done by ENT surgeons and also in some anaesthetic pre-assessment clinics. This excellent video, made by a team from NHS Lanarkshire, is a very useful guide to flexible nasendoscopy, including scope set up and a practical demonstration.
Chest X-ray: useful to identify whether the trachea is deviated or compressed.
CT: can be helpful in assessing airway calibre and identifying oedema and structural abnormalities.
MRI: particularly good at identifying soft-tissue abnormalities and a more recent development is 3-D navigation using special software (e.g. OsiriX).
Ultrasound: useful for visualising the cricothyroid membrane, tracheal position, thyroid gland and vascular structures and to evaluate the fasting status of the patient, as you will read in the next steps.
Functional status: stress-echocardiogram or cardiopulmonary exercise testing help determine the patient’s cardiovascular reserve, this is useful for risk stratification if major surgery is being considered.
In the “Downloads” section you will find an infographic summary for airway assessment.
Let’s move on to discuss the role of Point-of-Care Ultrasound in airway evaluation.
Kheterpal S, Healy D, Aziz MF, et al. Incidence, predictors, and outcome of difficult mask ventilation combined with difficult laryngoscopy: a report from the multicenter perioperative outcomes group. Anesthesiology 2013; 119: 1360–99