Upper Airway
The upper airway extends from the mouth and nose to the upper trachea. The upper airway functions as a passageway for gas flow; for filtering, warming, and humidifying the air; and for protecting the surfaces of the lower respiratory tract (Fig. 2.1). The upper airway also functions in phonation and in the senses of smell and taste.
The nasal cavity and the mouth meet at the pharynx (ie, the throat). The pharynx extends from the nasal cavities to the larynx, and it includes three parts: the nasopharynx, the oropharynx, and the laryn-gopharynx or hypopharynx. The pharynx is a passageway that is common to both the respiratory and digestive systems. The separation of the respiratory and digestive tracts occurs immediately below the laryngopharynx.
The nasopharynx is located at the posterior end of the nasal cavity, and it extends to the tip of the uvula. The mucous lining of the nasopharynx filters, warms, and moistens the air. The nasopharynx con-tains two pharyngeal tonsils (also called adenoids ) and the eustachian tube openings. Tissues of the naso-pharynx are extremely delicate and vascular. The improper or overly aggressive placement of tubes or airways may result in significant bleeding.
The oropharynx begins at the uvula , which is fleshy tissue that hangs down from the soft palate and into the posterior portion of the oral cavity. The posterior portion of the oral cavity opens into the oro-pharynx. The oropharynx extends to the upper rim of the epiglottis. The epiglottis is a small piece of cartilage located at the top of the larynx that prevents foreign material from entering the trachea during swallowing. The oropharynx functions in respiration and digestion. The anterior oropharynx opens into the oral cavity, which comprises the lips, cheeks, teeth, tongue, and hard and soft palates ( Fig. 2.2). The
Nasal cartilage
Fig. 2.1 Structures of the upper airway. (From Applegate: The anatomy and physiology learning system , ed 4, 2011, Saunders.)
anterior roof of the oral cavity is formed by the maxillary bone and is called the hard palate. The posterior portion of the roof of the mouth is called the soft palate because it is made up of mucous membrane, muscular fibers, and mucous glands. The cheeks form the walls, and the tongue dominates the floor of the oral cavity. Located on the lateral walls of the oropharynx are a pair of palatine tonsils that can cause a partial airway obstruction if they become excessively swollen. The space (or “pocket ”) between the base of the tongue and the epiglottis is called the vallecula . When performing orotracheal intubation, the epi-glottis is lifted out of the way to visualize the area during the passage of the tracheal tube between the vocal cords. The vallecula is an important anatomic landmark to identify when intubating a patient with
the use of a curved laryngoscope blade.
The laryngopharynx extends from the upper rim of the epiglottis to the glottis, which encompasses the true vocal cords and the space between them (ie, the glottic opening). Theglottis is the narrowest part of the adult larynx. The laryngopharynx is connected to the esophagus, and the laryngopharynx functions in respiration and digestion.
ACLS Pearl
In the unresponsive patient, a partial or complete airway obstruction can result when the muscles of the tongue and laryngopharynx relax, thus allowing the tongue and other soft tissues to block the opening of the laryngopharynx.
The larynx (ie, voice box) connects the pharynx to the trachea at the level of the cervical vertebrae. It conducts air between the pharynx and the lungs; it prevents food and foreign substances from entering the trachea; and it houses the vocal cords, which are involved in speech production. The larynx is a tubular structure made up of muscles, ligaments, and nine cartilages (see Fig. 2.1). The thyroid cartilage (ie, Adam’s apple) is the largest and most superior cartilage of the larynx. It is more pronounced in adult
males than adult females. The thyroid gland lies over the outer surface of the thyroid cartilage. The pyramid-shaped arytenoid cartilages of the larynx serve as a point of attachment for the vocal cords.
The arytenoid cartilages often serve as an important landmark during intubation.
The cricoid cartilage is inferior to the thyroid cartilage. It is considered the first tracheal ring, and it is the only complete ring of cartilage in the larynx. The other cartilages of the larynx are incomplete
Philtrum
Fauces (opening) Palatine tonsil Hard palate
Soft palate
Uvula
Tongue
Lower lip
Upper lip
Fig. 2.2 Frontal view into the open mouth showing the major structures within. (From Patton K, Thibodeau G: Anatomy &
physiology , ed 7, St. Louis, 2013, Mosby.)
26 CHAPTER 2 Airway Management
C-shaped rings on the posterior surface. The C-shaped rings are open to permit the esophagus, which lies behind the trachea, to bulge forward as food moves to the stomach. The narrowest diameter of the airway in infants and children who are younger than age 10 is at the cricoid cartilage. The cricothyroid membrane is a fibrous membrane that is located between the cricoid and thyroid cartilages. This site may be used for surgical and alternative airway placement.
ACLS Pearl
Stimulation of the larynx by a laryngoscope blade, tracheal tube, or suction catheter can result in bradycardia, hypotension, and a decreased ventilatory rate because the larynx is innervated with nerve endings from the vagus nerves. Monitor the patient closely for these effects and discontinue the treatment that is causing them if they appear.
Lower Airway
The lower airway extends from the lower trachea to the alveoli, and it functions in the exchange of oxygen and carbon dioxide. Air moves from the larynx through the glottic opening and into the trachea. The adult trachea is about twelve centimeters (cm) in length and has an inner diameter of about 2 cm. It divides or bifurcates into two separate tubes called the left and right primary bronchi (Fig. 2.3). The point where the trachea divides into the right and left primary bronchi is called the carina . The right bronchus
serves three lobes of the lung and the left bronchus serves two. The right primary bronchus is shorter, wider, and straighter or less angled than the left, because the heart occupies space in the left chest cavity.
Fig. 2.3 An adult and infant trachea showing the different angles of primary bronchi bifurcation. (From Kacmarek R, Stoller J, Heuer A: Egan ’ s fundamentals of respiratory care , ed 11, Elsevier, 2017.)
Therefore a tracheal tube that is inserted too far or foreign material that is aspirated is more likely to enter the right primary bronchus than the left.
The walls of the trachea are supported and held open by a series of 16 to 20 C-shaped cartilaginous rings. The area between the tracheal cartilages is composed of connective tissue and smooth muscle, which allow for changes in the diameter of the trachea. Tracheal smooth muscle is innervated by the
parasympathetic division of the autonomic nervous system.
Internally, the trachea is lined with a mucous membrane that contains cilia as well as mucus-producing cells. The cilia sweep foreign materials out of the airway and the mucus can also trap partic-ulate matter that is then expelled during coughing. Obstruction of the trachea will result in death if not corrected within minutes.
The primary bronchi branch into narrowing secondary and tertiary bronchi, which then branch into bronchioles. As the bronchi continue to divide into the lung tissue and become smaller passageways, they become bronchioles. Bronchioles are composed entirely of smooth muscle that is supported by connec-tive tissue. Bronchioles are responsible for regulating the flow of air to the alveoli. The stimulation of beta 2 receptor sites in the bronchioles results in relaxation of bronchial smooth muscle. After multiple subdivisions, the bronchioles divide into tiny tubes calledalveolar ducts , where gas exchange first becomes possible. These ducts end in alveoli, which are tiny, hollow air sacs. Each lung of an average adult con-tains about 300 million alveoli, and each alveolus is surrounded by a pulmonary capillary. Oxygen diffuses through the thin walls of the alveoli to the capillaries, and carbon dioxide diffuses from the capillaries to the alveoli.