Chapter 9: Essential Anatomy of the Airway

INTRODUCTION

A thorough understanding of airway anatomy is essential for the performance of any airway procedure.^1-10 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. An understanding of the anatomy of the airway will result in fewer attempts at intubation and improved success with fewer iatrogenic misadventures.

GENERAL ANATOMY

The upper airway comprises the nasal and oral cavities, the pharynx, and the larynx. The lower airway consists of the subglottic larynx, the trachea, and the bronchi.⁸ Airway management typically involves the upper airway, which is the focus of this chapter. The anatomy of the pharynx, larynx, trachea, and principal bronchi is depicted in Figure 9-1.¹¹

The nares serve as the functional beginning of the airway, namely warming and humidification of air.⁴ The mucosa of the nasal passage is extremely vascular and fragile. It is susceptible to bleeding with minimal manipulation during instrumentation to establish an airway. The nasal blood supply originates from branches of the internal and external carotid arteries. 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 time, it is more important in an emergency to definitively secure the airway using a straightforward oral intubation. Choose the more patent side of the nasal cavity for instrumentation in patients with nasal septal deviation.⁴

The sensory innervation of the upper airway is provided by branches of several cranial nerves. The mucous membrane of the nose is innervated anteriorly by the anterior ethmoid nerve (i.e., ophthalmic division of trigeminal nerve) and posteriorly by the sphenopalatine nerve (i.e., maxillary division of trigeminal nerve). The tongue is innervated by the lingual nerve on its anterior two-thirds (i.e., a branch of the facial nerve) and posterior one-third by the glossopharyngeal nerve. The glossopharyngeal nerve also innervates the adjacent areas, the palatine tonsils, the undersurface of the soft palate, and the roof of the pharynx.¹

The pharynx is a fibromuscular tube that extends from the base of the skull to the level of the cricoid cartilage. It connects the nasal and oral cavities with the larynx and esophagus, forming the oropharynx, nasopharynx, and hypopharynx. The velopharynx is the region of nasopharynx at the level of soft palate, a common site for upper airway obstruction in awake and anesthetized patients. An awake patient maintains the pharyngeal muscle tone to keep the airway patent. This tone is lost under general anesthesia, which promotes ...