36 Stridor
Stridor is a clinical finding reflecting partial extrathoracic airway obstruction. Although it is not pathognomonic for any single disease process, its presence can indicate a life-threatening upper airway obstruction. In addition, although stridor is traditionally thought to be inspiratory in nature, it can also be expiratory or biphasic, presenting in both phases of the respiratory cycle.
Etiology and Pathogenesis
Stridor can be caused by any upper airway obstruction. When thinking about the causes of stridor, it is helpful to first understand the anatomy of the larynx (Figure 36-1) and then to separate the causes of stridor into chronic and acute processes.
Chronic Stridor
The most common cause for inspiratory stridor is laryngomalacia, which accounts for approximately 75% of all cases of neonatal stridor. Laryngomalacia results from the immature cartilage of the upper larynx collapsing inward during inhalation, causing airway obstruction. Vocal cord dysfunction, the second leading cause of stridor in the neonatal period, can be congenital or iatrogenic, such as from damage to the left recurrent laryngeal nerve during ligation of a patent ductus arteriosus or from direct injury to the vocal cord during endotracheal intubation. Congenital subglottic stenosis occurs when there is incomplete canalization of the subglottic airway and cricoid rings. Subglottic stenosis is most often acquired after prolonged intubation in the neonatal period, usually in the setting of extreme prematurity. Tracheomalacia results from a defect in the tracheal cartilage that causes a “floppy” airway lacking the rigidity necessary to maintain patency. Tracheomalacia is the leading cause of expiratory stridor. Tracheal stenosis can be caused by the presence of complete tracheal rings instead of the normally C-shaped rings. Stridor can also result from tracheal compression caused by vascular rings such as a double aortic arch. Other less common causes of chronic stridor include laryngeal papillomas caused by maternal human papillomavirus infection, webs, cysts, hemangiomas, and laryngeal dyskinesia.
Acute Stridor
The causes of acute stridor are primarily infectious in cause with two notable exceptions, foreign body aspiration and allergic reaction. The most common cause of acute stridor is laryngotracheobronchitis, or croup (Figure 36-2). Croup is classically caused by parainfluenza virus but can also be caused by respiratory syncytial virus, influenza, adenovirus, and Mycoplasma pneumoniae. Bacterial tracheitis, usually caused by Staphylococcus aureus, is an uncommon but life-threatening condition that occurs most frequently as a bacterial superinfection in patients who have viral croup.
Retropharyngeal and peritonsillar abscesses are common infections that can present with acute stridor. Both infections are usually polymicrobial, including β-hemolytic streptococci; oral anaerobic bacteria; and in retropharyngeal abscess, S. aureus. Finally, epiglottitis, traditionally caused by Haemophilus influenzae type B (Hib), is now a rare cause of stridor as a result of the widespread use of the conjugated Hib vaccine.
Clinical Presentation
Chronic Stridor
Laryngomalacia can present at birth but usually presents at 2 to 4 weeks of age. The inspiratory stridor of laryngomalacia is exacerbated when the infant lies supine, cries, or when feeding and is alleviated when the infant is prone.
Vocal cord paralysis can be unilateral or bilateral. Bilateral vocal cord paralysis results in aphonia and high-pitched biphasic stridor, with significant respiratory distress. Unilateral paralysis can cause inspiratory or biphasic stridor, as well as a weak or hoarse cry.
Whereas subglottic stenosis and vascular rings may likewise present with inspiratory or biphasic stridor, tracheomalacia usually presents with expiratory stridor. Tracheomalacia may present with a monophonic wheeze if the obstruction is intrathoracic.
Acute Stridor
Croup occurs most commonly in children age 6 months to 2 years and is characterized by a harsh cough described as “barky” or “seal-like.” Associated upper respiratory symptoms are common, and stridor can be mild, occurring only with crying, or in severe cases, can occur at rest with severe respiratory distress. Bacterial tracheitis is a rare complication of croup, and in addition to stridor. the child also will have high fever and a toxic appearance.
Retropharyngeal abscess usually occurs in children younger than 6 years old before the retropharyngeal lymph nodes atrophy. Patients often have a viral prodome followed by the abrupt onset of high fever, limited neck movement (especially resistance to extension), and occasionally stridor. Unilateral neck swelling may occur as the infection tracks from the retropharyngeal space, and a bulge of the posterior oropharynx may sometimes be present on physical examination. Peritonsillar abscess occurs in preadolescents and adolescents and can present with sore throat, trismus, dysphagia, a “hot potato” or muffled voice, and tender unilateral neck swelling. Asymmetric tonsils, deviation of the uvula, and a fluctuant area are present on physical examination (Figure 36-3). Stridor may be heard if tracheal compression is present. Epiglottitis classically presents with the abrupt onset of high fever, stridor, drooling, “tripod” positioning, and toxicity.
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