Abstract
Failure to properly assess and identify possible difficulties with airway management and incorporate these findings to airway management strategies can lead to a poor clinical outcome. A thorough patient history review and physical examination, including bedside airway assessment, often reveal either congenital or acquired clinical conditions that may affect airway management. Ultrasound, radiographic studies and bedside flexible endoscopy for airway assessment are often necessary to understand the mechanism of pathophysiology of the lower airway. The advancement of technology, such as three-dimensional imaging, cone-beam computer tomography and virtual endoscopy, etc., is resulting in the emergence of potential future airway assessment tools. However, the ideal assessment tool for difficult airway management does not exist and unanticipated difficulties often occur. Using multiple tests to predict difficulty in airway management is better than any single test used in isolation. In addition, adverse human factors can significantly impact airway management. The importance of incorporating cognitive aids in our routine practice cannot be underestimated. Airway assessment forms the first part of any airway management strategy, including the use of certain medications and airway techniques. As practitioners, we must rise to the occasion and perform best clinical practice; there can no longer be a disconnect in what we know and what we do. We need to be the strong link in the chain in providing safe and quality care for our patients.
Introduction
Recommended by the major anaesthesia societies around the world, pre-anaesthetic airway assessment is essential for all patients undergoing anaesthesia care. An adequate airway assessment provides fundamental information to aid developing airway management strategies. Conventional airway assessment focusses on the patient’s airway characteristics to stratify risk factors for a difficult airway, in which the success of direct laryngoscopy and intubation, placement of supraglottic airway (SGA) and face mask ventilation are challenging. The primary goal of airway evaluation is to ensure that potential issues are identified and safety measures are adequately addressed. With the advancement of technology, more advanced airway tools and techniques continue to be added to the toolbox such as transnasal high flow humidified oxygen and the various video-assisted tracheal intubation tools and their corresponding accessories. These new tools are expanding our vision and advancing airway management methodology. The airway assessment should also reflect these changes; and the strategy of risk stratification should be focussed on the clinical feasibility of using available advanced airway tools and techniques and their corresponding risk factors of failure. In practice, failure of airway management is often the escalating result of composite errors. Thus, assessing the impacts of human factors including the influences of environment, team and person in airway management should be a routine practice and is addressed in this chapter as well.
Conventional Airway Assessment Strategies
Conventional airway assessment includes a review of the patient’s history, diagnostic imaging and a bedside interactive airway examination. The assessments aim to detect potential risks for difficulty in direct or videolaryngoscopy and tracheal intubation, SGA insertion, face mask ventilation and increased risk of pulmonary aspiration, intolerance of apneoa and difficulty in oxygen delivery to the lungs. The recommended components of pre-anaesthetic airway assessment are listed in Box 5.1.
History of previous airway difficulty
Medical conditions that could be associated with difficulty
History of previous surgery or radiotherapy to the head, neck or mediastinum
External overall assessment
Bedside interactive tests
Accessibility of the cricothyroid membrane
Implications of the presenting disease with regard to airway management
Review of relevant diagnostic imaging
History
The patient history should be evaluated for potential risk factors. Clinical conditions associated with a difficult airway may be the result of congenital abnormalities of the face and upper aerodigestive tract; airway pathology such as head and neck trauma, airway infection, tumour or acquired airway defects; and chronic medical conditions or diseases.
Congenital Conditions
Children with congenital syndromes associated with difficult airway management are usually seen in an anaesthesia paediatric clinic. Some of the common clinical features associated with difficult airway management found in these syndromic patients include limited neck mobility and shortness of the neck resulting from fusion of cervical vertebrae in Klippel–Feil syndrome, micrognathia and retraction of the tongue due to mandibular hypodysplasia in Pierre Robin syndrome and Treacher Collins syndrome, and macroglossia and small mouth opening in Beckwith–Wiedemann syndrome and Goldenhar syndrome. Down syndrome (trisomy 21) is associated with multiple airway issues, including macroglossia, short neck and atlantoaxial instability. Multiple dysmorphic features may coexist in the same patient. Predicting airway difficulty is based on assessment of the abnormalities and their impacts on airway management. However, for patients with an abnormal aerodigestive tract such as mucopolysaccharidosis in Hurler syndrome and subglottic stenosis in Down syndrome, prediction of a difficult airway is mainly based on a previous diagnosis, history of airway obstruction such as significant sleep apnea, or findings of bedside flexible endoscopy.
Airway Pathology
Various airway pathologies or acquired tissue defects from previous surgery are seen in head and neck patients. The major challenges in airway management in these individuals are the results of obstruction of airflow or the intubation path or changes in airway anatomy. A patient’s previous airway history is unlikely to be helpful if there has been disease progression. Further, because disease locations vary, conventional airway assessment tools may not be reliable in evaluating the impact of disease on the airway. For those who have disease in the oral cavity or oropharynx, direct visual inspection is often sufficient for forming a management plan. For patients with a lesion in the deep airway, bedside flexible endoscopy (see Chapter 6) and reviewing imaging studies are essential. Assessing the airway in patients with head and neck pathology requires special considerations and methods. An example of this is the novel TRS score for patients with head and neck pathology. In this system, the airway is evaluated with the components of Tumour, Radiation and Surgery (TRS) with each component rated from 0 to 2 to reflect the minimal, moderate and severe impacts of tumour, radiotherapy and surgery to airway management respectively (Table 5.1). The cumulative score not only indicates the potential difficulty of airway management but is also proposed by the authors as an ‘airway time-out’ tool for the entire team to perform prior to managing the airway.
| Score | T (Tumour) | R (Radiotherapy) | S (Surgery) |
|---|---|---|---|
| 0 | Small tumour without respiratory symptoms | Slight skin change without restriction of neck mobility | Uncomplicated neck dissection without involvement of airway |
| 1 | Large oropharyngeal tumour with some difficulty breathing but no stridor | Skin discolouration and thickening without impedance of neck motion | Minor surgery in upper aerodigestive track without the need for reconstructive surgery |
| 2 | Bulky laryngeal tumour resulting in stridor | Acute or chronic radiation-related complications including microsites, dermatitis, skin sloughing and oedema, or tissue fibrosis with loss of mobility or anatomical landmarks | Extensive upper aerodigestive track resection with complex reconstruction with various flaps |
Computed tomography (CT) is the most commonly used imaging modality in patients undergoing head and neck surgery. The findings of the CT scan are used to delineate the extent of the pathology and how it affects the airway. Because the effects of disease on the airway may be asymmetric, the series of images from all three planes (transverse, coronal and sagittal) should always be reviewed. In addition to various airway pathologies, the tonsils (especially the lingual tonsil), vallecular space and hypopharyngeal volume may be evaluated with CT imaging in a patient with a grossly normal airway. A hypertrophic lingual tonsil imposes a mass effect in the hypopharyngeal space and thus increases the difficulty of laryngoscopy and visualisation of the glottis (Figure 5.1a–c).
However, due to the limits of CT imaging in spatial resolution, variations in imaging methods, and variation in phase of the respiratory cycle at the time of image capture, CT imaging cannot be relied on to accurately measure the calibre of the airway and to adequately estimate the level of tissue oedema of various anatomical sites.
Medical Conditions Associated with Difficult Airway
Airway management can be complicated by the effects of chronic diseases. Three conditions with particular relevance are rheumatoid arthritis, ankylosing spondylitis and obstructive sleep apnoea.
Rheumatoid arthritis is characterised by destructive inflammation in the joints, principally affecting the small joints. Involvement of the temporomandibular and/or cricoarytenoid joints and the cervical spine may impose significant impacts on airway management. In patients with rheumatoid arthritis, the atlantoaxial joint may be affected with attenuation of the transverse ligament and erosion of the odontoid process.
While radiographic evidence of atlantoaxial subluxation is present in up to 40% of patients with rheumatoid arthritis, clinical syndromes are uncommon. Four atlantoaxial subluxation subtypes have been described: anterior, posterior, vertical, and lateral rotatory; anterior is the most common. When subluxation is present neck movement should be minimal during airway management. However, the neck range of motion varies by subtype. Table 5.2 summarises some of the clinical characteristics of atlantoaxial subluxation. A routine preoperative X-ray to rule out cervical joint subluxation is controversial.
Table 5.2 Subtypes of atlantoaxial subluxation
Related posts:
Chapter 6 – Pre-anaesthetic Airway Endoscopy, Real and Virtual
Chapter 7 – Ultrasonography for Airway Management
Chapter 15 – Tracheal Tube Introducers (Bougies), Stylets and Airway Exchange Catheters
Chapter 22 – The Airway in Obstetrics
Chapter 31 – Airway Management during CPR
Chapter 26 – Ear, Nose and Throat Surgery: Airway Management
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