Tracheal Intubation and Endoscopic Anatomy

Introduction

Proficiency in airway management and tracheal intubation requires a firm foundation of knowledge in airway anatomy. This chapter provides an overview of airway anatomy for tracheal intubation with conventional laryngoscopy, videolaryngoscopy (GlideScope), and flexible fiberoptic bronchoscopy. Airway assessment and recognition of a difficult airway are also reviewed. Although the numerous airway management devices include video laryngoscopes, optical stylets, rigid fiberoptic laryngoscopes, and supraglottic ventilatory devices (beyond the scope of this chapter), all require similar anatomic considerations.

Airway Anatomy

The pulmonary system consists of lungs and a series of airways that are subdivided into upper and lower segments.

Upper Airway

The upper airway consists of the nose, mouth, pharynx, and larynx. There are three pharyngeal segments: (1) nasopharynx, posterior to the soft palate; (2) oropharynx, posterior to the tongue from the tip of the uvula to the tip of the epiglottis; and (3) laryngopharynx, posterior to the epiglottis (Fig. 45-1). The pharyngeal segments are collapsible because the anterior and lateral walls lack bony support.

FIGURE 45–1 Sagittal section of pharynx.

Inspiratory patency of the pharynx is maintained primarily by contraction of the tensor palatine, genioglossus, and hyoid bone muscles. Loss of muscle tone leads to pharyngeal collapse. During general anesthesia or intravenous sedation, the upper airway becomes obstructed because of a decrease in the anteroposterior diameter of the pharynx at the level of the soft palate and epiglottis. Many anesthetic agents and sedative drugs diminish the action of pharyngeal dilator muscles, which promotes pharyngeal collapse and airway obstruction.

The larynx serves as the connecting structure between the upper and lower airways (Fig. 45-2). The adult larynx extends from the 4th to the 6th cervical vertebra, and it is composed of nine cartilages, with six paired and three single. The three single cartilages include the thyroid, cricoid, and epiglottis. The paired arytenoid cartilages secure the vocal cords to the larynx. The endolarynx is constructed of two pairs of folds that form the supraglottis and glottis.

FIGURE 45–2 Views of larynx.

The internal and external laryngeal muscles control vocal cord length and tension and movement of the larynx as a whole. These muscles aid in swallowing, respiration, and vocalization and are integral in preventing aspiration into the trachea and lower airway. The hyoid bone suspends and anchors the larynx.

Note the location of the superior laryngeal nerve (important for nerve block anesthesia) adjacent to the hyoid bone (Fig. 45-2). Motor innervation of the laryngeal muscles is through the superior laryngeal nerve (cricothyroid muscle) and recurrent laryngeal nerve (remainder of laryngeal muscles). Stimulation of the supraglottic region, especially where the piriform recesses blend with the hypopharynx, can result in laryngospasm with complete glottic closure.

Nose and Nasopharynx

Nasotracheal intubation is an alternative approach to orotracheal intubation. The two nasal fossae extend from the nostrils to the nasopharynx. The nasal fossae are divided by the midline cartilaginous septum and medial portions of the lateral cartilages (Fig. 45-3, A). The nasal fossa is bounded laterally by inferior, middle, and superior turbinate bones. The mucosa covering the middle turbinate is highly vascular, receiving its blood supply from the anterior ethmoid artery, and also contains a large plexus of veins. The middle turbinate is susceptible to avulsion by trauma and is associated with massive epistaxis. The paranasal sinuses (sphenoid, ethmoid, maxillary, and frontal) open into the lateral wall of the nose. The inferior turbinate usually limits the size of the nasotracheal tube.