The concepts of difficult airways are frequently discussed in the field of anesthesia. Every patient that is anesthetized goes through an airway assessment to determine the potential of a difficult airway. Different tests and observations can help point to a potential difficult airway, but nothing is concrete.
The potential difficult airway scenario can be found in many locations outside of the typical operating theatre. Prehospital providers are the first individuals who could encounter a difficult airway patient. The emergency department (ED), intensive care unit (ICU), and any other part of a hospital could entertain a difficult airway situation.
The American Society of Anesthesiologists (ASA) defines a difficult airway as a clinical situation in which anesthesia providers experience difficulties in facial mask ventilation and/or tracheal intubation. 1 Additionally, all methods of airway manipulation, including the use of airway adjuncts and supraglottic airway devices (SAD), may fail.6 Although the ASA referenced anesthesia providers only, the problems of being unable to mask ventilate and/or intubate the patient can happen with any properly trained healthcare provider.
Three approaches are recommended to evaluate an airway: 1) evaluation of the airway history, 2) physical examination, and 3) additional evaluation in some patients with anticipated airway difficulty.1
Assessment of the airway history may reveal a difficult airway, and risk factors can include age, obesity, obstructive sleep apnea (OSA), and history of snoring.3 A history of OSA should be sought, as it is positively correlated with difficult mask ventilation and intubation.8 Symptoms suggestive of OSA include snoring and daytime lethargy and are more common in patients who are male, have a body mass index over 35, are aged over 50 years, and have a neck circumference greater than 40 cm.6
Difficult intubation or extubation has also been found to occur in patients with mediastinal masses and in a variety of acquired or congenital disease states (e.g. ankylosis, degenerative osteoarthritis, subglottic stenosis, lingual thyroid or tonsillar hypertrophy, and Treacher Collins, Pierre Robin, or Down syndromes).1
When possible, it is important to use as many airway assessment tools as possible to help guide the practitioner in determining whether or not they may be facing a difficult airway situation. Some of the most common are mouth opening, the upper-lip bite test (ULBT), and head and neck mobility.
Interincisor gap is important to assess when performing a direct laryngoscopy or video laryngoscopy because the size of the mouth opening can affect the ability to introduce a laryngoscope device and to create a direct line of sight with the laryngeal opening.10 Mouth opening is vital for most airway interventions and is measured as the inter-incisor distance.6 A distance of <4 cm is predictive of a difficult airway.3
The ability to prognath is assessed through the upper lip bite test, and if the patient is unable to bring the lower incisors in front of the upper incisors, a difficult airway can be expected.3 The ULBT has three classifications:11
Assessment of a ULBT class C indicates a potential difficult laryngoscopic view, whereas class A indicates a good view using conventional laryngoscopy.5
Proper atlanto-occipital joint mobility is required for an adequate sniffing position.9 The sniffing position is important because it helps to improve direct laryngoscopic views by promoting displacement of the tongue by better aligning the oral, pharyngeal, and laryngeal axes.9 Evaluation of atlanto-occipital joint extension is conducted with the patient seated upright in a neutral face-forward position; the patient is then asked to lift the head back with the chin up as far as possible.9 When extension is reduced to 23 degrees, visualization may become difficult.11
Other clinical signs indicating a difficult airway are a large neck circumference and a high Mallampati score.2
Neck circumference (NC) >43 cm has been associated with difficult intubation in obese patients.7
Mallampati classification is a method of grading the visibility of pharyngeal structures and is divided into four classes.3 In class I, the soft palate, uvula, fauces, and pillars are visible. In class II, the soft palate, uvula, and fauces are visible. In class III, the soft palate and the base of the uvula are visible, whereas in class IV, only the hard palate is visible. Mallampati class III or IV is associated with difficult or impossible tracheal intubation.4
The difficult airway patient can be found in any area of healthcare, from pre-hospital to the ED to the operating room. Understanding some assessment tools to quickly determine the potential for a difficult airway can leave the health care provider ready with the tools necessary to protect the patient. “Difficult Airways—Part 2“ will describe some of the airway devices available to help with the most difficult airways.