Chapter 1

A thorough understanding of anatomy is essential for the performance of any medical procedure. Untoward events due to a procedure are usually the result of inexperience and/or an inadequate understanding of the regional anatomy. The anatomy of the airway and airway procedures are no exception. From the evaluation of external anatomic landmarks to the performance of nerve blocks for fiberoptic intubation, an understanding of the anatomy of the airway will result in fewer attempts at intubation and improved success with fewer iatrogenic misadventures.

The airway comprises the nasopharynx, oropharynx, larynx, and trachea (Figure 1-1). The mucosa of the nasal passage is extremely vascular and fragile and therefore susceptible to trauma. It is wise to consider the use of a vasoconstricting agent, when appropriate, to help avoid epistaxis which may obscure further attempts at securing the airway. Although patients tolerate nasal intubation better than oral intubation for a longer period of time, it is more important in an emergency to definitively secure the airway using a straightforward oral intubation. The mucous membrane of the nose is innervated anteriorly by the anterior ethmoid nerve (ophthalmic division of trigeminal nerve) and posteriorly by the sphenopalatine nerve (maxillary division of trigeminal nerve). The tongue is innervated by the lingual nerve on its anterior two-thirds (a branch of the facial nerve) and by the glossopharyngeal nerve posteriorly. The glossopharyngeal nerve also innervates the adjacent areas, including the palatine tonsils, the undersurface of the soft palate, and the roof of the pharynx.1 The anatomy of the oropharynx is discussed further under “Airway Evaluation” and the anatomy of the larynx is covered in the next section.

###### Figure 1-1

Anatomy of the airway. The drawing is a midsagittal section through the head and neck.

The trachea measures 15 cm in an average adult. It bifurcates at the fifth thoracic vertebra into two primary bronchi. The primary bronchi subsequently branch into three secondary bronchi on the right and two secondary bronchi on the left. The angle between the primary bronchus and the trachea on the left is more acute than on the right. This is due to the heart being located on the left side. This is clinically significant during aspiration and endobronchial intubations. Because of the more direct path on the right side due to the obtuse angle of the primary bronchi, objects (food, fluid, foreign bodies) end up in the right lung. The tracheal mucosa removes waste products by producing and moving mucus toward the pharynx via ciliary action. The trachea has a rich innervation from the vagus nerve, which permits a vigorous cough reflex (accompanied by hypertension and tachycardia) if a foreign body is aspirated.

The diameter of the trachea varies between normal adult males and females. It ranges from about 15 to 20 mm. Since the external diameter of a 7.5 mm internal diameter ...

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