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Upper airway disorders 133
The pediatric airway has many unique features that differ depending on the age of the child (Table 6.1). The larynx is significantly higher in infants and in children. The inferior margin of the cricoid cartilage lies at approximately the level of the second or third cervical vertebra in the infant and descends to the sixth cervical vertebra by puberty (Brown, 2000). The larynx is also located more anterior and superior in the neck in the neonate, allowing approximation of the epiglottis and palate. This allows the neonate to be an obligate nose breather for the first several weeks to months of life. This anatomical situation does allow the healthy neonate the ability to both breath and swallow simultaneously, which is not pos- sible as the larynx descends.
The larynx is composed of cartilage and ligaments. There are three large cartilages and three small cartilages (Becker et al., 1989). The larger carti- lages include the thyroid, epiglottis, and cricoid cartilage. The thyroid cartilage forms the main skeleton of the larynx; however, it does not assume its adult configuration until adolescence. The epiglottis cartilage protects Figure 6.1 Anatomy of the oropharynx, hypopharynx, trachea, and larynx.
Reprinted from Andresen et al. (2008), with permission from the editors.
Frontal sinus
Sella turcica Sphenooccipital suture Pharyngeal tonsil
Pharyngobasilar fascia
Uvula
Aditus of larynx Thyroid cartilage Vocal fold (cord)
Cricoid cartilage Trachea Esophagus
Cricopharyngeal muscles
Esophageal muscles Transverse arytenoid muscle Anterior longitudinal ligament
Pharyngeal opening of auditory (eustachian) tube
Pharyngeal constrictor muscles
Pharyngeal tubercle of occipital bone Sphenoid sinus
Nasal septum Nasopharynx Soft palate
Hard palate
Oral cavity Body of tongue Palatine tonsil Oropharynx Foramen cecum Lingual tonsil Genioglossus muscle
Geniohyoid muscle Epiglottis Hyoid bone Hyoepiglottic ligament Thyrohyoid membrane
Laryngopharynx (hypopharynx) Root of tongue
Mandible Incisive canal Palatine glands
134 Nursing Care in Pediatric Respiratory Disease
the airway from food, liquids, and saliva during swallowing. The cricoid cartilage is located inferior to the thyroid cartilage and is the first ring of the trachea. It is the only rigid circular structure of the airway, which in turn produces the narrowest fixed point in the pediatric airway. In contrast, the narrowest portion of the adult airway is at the level of the vocal cords (Cotton & Willging, 1999). The smaller cartilages include the arytenoid, corniculate, and the cuneiform. The hyoid bone is the only bone in the framework of the larynx. It is a landmark in the neck, a movable horseshoe- shaped bone at the base of the tongue.
The laryngeal muscles are responsible for elevation and depression of the larynx (extrinsic muscles) as well as movement of the vocal cords (intrinsic muscles) (Healy, 1989). The development of all supporting airway cartilage and small airway muscles is incomplete until school age; this may predispose the infant and young child to malacia.
Physiologically, the role of the larynx is multifactorial. It acts as a valve during the swallowing process, closing the airway to prevent aspiration and to allow delivery of food and liquids to the esophagus. During this process, the vocal cords close and the larynx elevates up against the epi- glottis. Second, the larynx allows for vocalization. As air is exhaled from the lungs, it travels up through the vocal cords, which vibrate, causing phonation (Brown, 2000). Other aspects of speech are accomplished by structures higher up as the air is exhaled. Articulation is achieved through movement of the soft palate, tongue, and lips. Tone and quality of speech is affected by resonation through the pharynx, sinuses, and nasal passage.
The larynx not only serves as an air passage but also as a filter as it clears the respiratory tract of secretions through a voluntary cough. The cough is produced by forcibly closing the glottis.
The recurrent laryngeal nerve and the superior laryngeal nerve are branches of the vagus nerve (cranial nerve X) that supply innervations of the larynx (Becker et al., 1989). The recurrent laryngeal nerve is located just lateral to the trachea and supplies motor innervation to the intrinsic laryngeal muscles, which are responsible for vocal cord mobility. The left Table 6.1 The pediatric airway is different from the adult airway.
Development of supporting airway cartilage and small airway muscles is incomplete until school age.
The larynx is higher in the child. The cricoid cartilage lies at the level of the third cervical vertebra in the infant and descends to the sixth cervical vertebra at puberty.
The thyroid cartilage does not assume its adult configuration until adolescence.
The recurrent laryngeal nerve lies just lateral to the trachea. In addition, a pretracheal pad of fat is generally present in infants.
The articulation between the head and neck is more mobile in infants and the chin may easily deviate from the midline during surgery.
The airways are smaller (narrower and shorter).
Upper airway disorders 135
branch of the recurrent laryngeal nerve loops under the aortic arch above the pulmonary artery. The trachea is a flexible cylindrical cartilaginous muscular tube extending vertically from the larynx to its bifurcation (carina) into the right and left mainstem bronchi. Its purpose is to trans- port warmed, filtered, and humidified air to the lungs for respiration.
The trachea is composed of 16–20 C-shaped hyaline cartilage “tracheal rings” (Becker et al., 1989). The posterior wall of the trachea (open part of the C) is composed of smooth muscle and connective tissue that allows the diameter of the trachea to change. The posterior trachea abuts the esophagus and the soft posterior wall allows the esophagus to expand during swallowing. The vagus nerve and the sympathetic system inner- vate the trachea.
It is no surprise that the larynx and trachea are smaller, both narrower and shorter in infants and in children versus adults. The vocal cords in the newborn infant are 6–8 mm long. The posterior glottis transverse length is approximately 4 mm, and the subglottis has a diameter of about 5–7 mm.
The tracheal length is 4 cm long (10–13 cm in an adult), with a diameter of 3.6 mm (25 mm in an adult) (Becker et al., 1989). These measurements leave little margin for obstruction.
Pouseuille’s law states that flow within the system is related to the radius of the tube to the fourth power. Resistance is related to the inverse of the radius to the fourth power. One millimeter of tracheal edema will have little effect on the airway of an adult or adolescent; however, it may cause serious airway obstruction and resulting respiratory compromise in an infant or a young child (Table 6.2).