Chapter 6 – Pre-anaesthetic Airway Endoscopy, Real and Virtual

Abstract

This chapter explores the well-established skill of upper airway endoscopy as a tool for assessing the upper airway and planning the best airway management approach for anaesthesia. It also describes the emerging modality of virtual airway endoscopy, which can examine both upper and lower airway, and its potential roles. Both techniques focus on examination of the air column within the airway (Greenland’s ‘middle column’) but can reach beyond the sight of the naked eye. Both techniques have potential to aid understanding of the patient’s airway anatomy and pathology and can enable improved airway planning.

Chapter 6 Pre-anaesthetic Airway Endoscopy, Real and Virtual

William Rosenblatt and Imran Ahmad

In Greenland’s three column model of the airway (see Chapter 14), the ‘middle column’ (i.e. the airway passage beyond the oropharynx) is the airspace most of which is beyond the vision of the unaided eye of the airway examiner. Long appreciated and routinely examined by the otolaryngologist, this anatomical and functional region of the airway is too often ignored by the anaesthetist or other clinician planning airway management. Ovassapian identified lingual tonsil hyperplasia (Figure 6.1) as a principal cause of unanticipated difficulty with direct laryngoscopy in patients who appear otherwise normal. Additionally, pathological lesions extending into the middle column from the supraglottic larynx (Figure 6.1), base of tongue and the glottis itself may likewise contribute to failure to see or intubate the larynx. Fortunately, most of the patients harbouring these pathologies will be known at the time of presentation to the operating room. However, uncontrolled data suggest clinicians may be poor at predicting difficulty – in 17% of patients with relevant pathology, the lesions interfere with routine airway management, while in 63% of these patients with an anticipated difficult airway based on clinical examination, no difficulty is encountered.

Figure 6.1 Findings causing unanticipated difficult direct laryngoscopy (a) Lingual tonsil hyperplasia and (b) epiglottic cyst.

A thorough examination of the middle column has been shown to reduce the number of patients who are falsely identified as having a difficult- or easy-to-manage airway. A caveat is that this applies to patients without lingual tonsil hypertrophy, as this group has not been studied, though similar results might be anticipated.

Otolaryngologists commonly examine the middle-column region in their initial diagnostic and planning assessments especially when a lesion is known or suspected. This may be by CT, MRI or ultrasound imaging, use of an upper airway mirror or endoscopic examination. While, it might be expected that the description of these examinations would be helpful to the airway manager, the otolaryngologist’s interpretation can often be irrelevant and even misleading in this respect. The otolaryngologist’s examination focusses on the extent of disease, the preservation of function and the immediacy of intended surgery, i.e., the level and likely progression of airway obstruction, pathological bleeding, interference with oral nutrition etc. The examination is not concerned with factors that may affect airway management such as the ability to face mask ventilate, place a supraglottic airway or intubate the larynx and trachea. All modalities of imaging may be deceptive in both underestimating the role of significant pathology or because they only capture a single point in time. Further, they are static images, often acquired with the patient only supine (CT, MRI), or only sitting (mirror and nasendoscopy) and with the head and neck in a neutral position, which may not be the position adopted during anaesthesia. Therefore, though these examinations may be helpful to the airway manager, they cannot be conclusive when planning management.

Preoperative Endoscopic Airway Examination with Nasendoscopy

Fortunately, techniques that enable bedside, point-of-care evaluation of the middle column are readily available to the anaesthetist, and in many cases are well within existing skill sets. Endoscopic evaluation of the upper airway can rapidly and safely be performed at the bedside, whether in a preoperative evaluation clinic, holding area or in the operating room. A flexible optical bronchoscope or nasendoscope can be used, and this requires minimal patient preparation. Rosenblatt and colleagues found that preoperative endoscopic airway examination (PEAE) altered the intended airway management plan – developed on clinical data alone – in one quarter of cases. Most examinations were reassuring compared with clinical decision making and prompted routine induction of anaesthesia and airway management. Conversely, in a small group of patients, PEAE revealed significant lesions that were not suspected from patient history and physical examination, and awake management was chosen.

When performing PEAE, a small intubating bronchoscope or nasendoscope is used. A device with an external diameter < 4 mm is most comfortable for the patient. The patient’s nares are prepared with a topical vasoconstrictor (e.g. oxymetazoline, phenylephrine) and a topical anaesthesia (e.g. 50 mg of lidocaine as spray, jelly or ointment) is placed using a cotton swab or soft catheter-on-syringe. Some patients will tolerate very small endoscopes without any topical anaesthesia. Anaesthetic preparation beyond the nose (i.e. the pharynx and hypopharynx) is not needed because the endoscope transverses these areas tangential to the sensitive posterior pharyngeal wall and little gag reflex is elicited provided the endoscope is controlled so as to not touch the superior side of the epiglottis. The endoscope is introduced into a naris, and a position below the inferior turbinate is maintained (Figure 6.2). Obstruction or pain should prompt further preparation and/or attempts in the opposite naris. It is common that the patient experiences some discomfort (usually pressure) as the turbinates are passed by the endoscope tip. Once the nasopharynx is reached, the examination should not be disturbing. Fogging of the endoscope objective lens may be resolved with a purposeful touch onto the posterior nasopharyngeal wall. At this position the hinged end of the endoscope is deflected downward and the examination continues. Generally, most information will be gained once the epiglottis is seen. Should the operator need to pass the point at which the glottis is seen, the examination should proceed slowly and deliberately, following the patient’s respiratory phases which lift the epiglottis off the posterior pharyngeal wall during inspiration. The arytenoids, false and true vocal cords should not be contacted. Asking the patient to breathe more deeply, protrude their jaw or to repeat the letter ‘e’ may improve the ease with which the glottis is seen.