Stridor is a variable, high-pitched respiratory sound that can be assessed during breathing. Typically, stridor is produced by the abnormal flow of air in the airways, usually the upper airways, and most prominently heard during inspiration. However, it can also be present during both inspiration and expiration. Stridor can be due to congenital malformations and anomalies as well as in the acute phase from life-threatening obstruction or infection. The diagnostic approach may include x-rays or bronchoscopy by a trained specialist to ascertain the etiology when there is diagnostic uncertainty. It should be noted that in infants and young children, a small amount of inflammation can result in significant and rapid airway obstruction.
The etiologies for stridor differ depending on whether the patient is pediatric or an adult. For pediatrics, the most common causes of acute stridor include croup, foreign body aspiration. However, there are many other causes. The cause of stridor can further be differentiated based on acuity and based on congenital versus noncongenital causes.
Congenital Causes of Stridor in Pediatrics
Noncongenital Causes of Stridor in Pediatrics
(See table below)
Most common cause of chronic stridor in infants is laryngomalacia.
The epidemiology of stridor is dependant on the original cause for the stridor. Generally, stridor is more common in pediatrics than adults.
With croup, for example, the peak incidence is between 6 months to 36 months, where there are about 5 to 6 cases per 100 toddlers. There is also a slight male predominance of 1.4:1.
Moreover, foreign body aspiration accounts for more than 17,000 emergency department visits per year in the United States, with most cases occurring before the age of 3 years.
The pathophysiology of stridor is based upon the anatomic location involved as well as the underlying disease process. Narrowowing of the supraglottic areas can occur rapidly because there is no cartilage in these areas. The subglottic area is of most concern in infants in which minimal airway narrowing here can result in dramatic increases in airway resistance.
An obstruction in the extrathoracic region causes inspiratory stridor. During inspiration, the intratracheal pressure falls below the atmospheric pressure, causing a collapse of the airway.
An obstruction in the intrathoracic region causes expiratory stridor. During expiration, the increased pleural pressure compresses the airway causing a decrease in the airway size at the site of the intrathoracic obstruction.
Both inspiratory and expiratory stridor occur because of bacterial tracheitis and foreign bodies.
Laryngeal webs and vocal cord paralysis occur due to a fixed airway obstruction, which does not change with respiration.
Initial evaluation should begin with a rapid assessment of the patient's airway and effort of breathing. First, ensure that the airway maintains patent and can move air in and out of the lungs. Asses the patient's rate and depth of breathing, and evaluate for hypoxia or cyanosis and if the patient looks like they are decompensating secondary to fatigue.
If the patient is hemodynamic stable with stridor, obtain a thorough history of present illness, review of systems, and medical history. Keys to the correct diagnosis can be delineated based on patient age, acuity of onset, history of exposures to allergens or infectious sources. In the stable patient with stridor, additional testing including imaging, radiography, and endoscopy may be performed.
In the patient is unstable, there may be signs of respiratory distress, gasping, drooling, fatigue, cyanosis, and these signs prompt a more rapid evaluation and rapid management to ensure airway patency. This can include endotracheal intubation or emergency surgical airway.
Laboratory testing may include a complete blood count (CBC), if an infectious source is suspected, however, this is usually not necessary for diagnosis. A rapid viral panel may be obtained to assess for parainfluenza viruses in the pediatric patient.
Radiography including a lateral plain film may be obtained to assess for the size of the retropharyngeal space, in which a widened space may indicate a retropharyngeal abscess. A mnemonic can be used "6 at C2, and 22 at C6" to remember that the normal retropharyngeal space should not be greater than 6mm at the level of C2 and not more than 22 mm at the level of C6. This view may also aid in visualizing of an enlarged epiglottis. An anteroposterior view to assessing for subglottic narrowing such as the "steeple" sign in croup. A chest radiograph can be obtained in suspected foreign body aspiration. However, a negative chest radiograph does not rule this out.
Computed tomography (CT) can be considered when there is diagnostic uncertainty in the stable patient with stridor. CT of the chest and neck can evaluate for an infectious source such as cellulitis as well as stenotic lesions, or foreign bodies. Magnetic resonance imaging (MRI) can help discern tracheal stenosis in pediatric patients.
Laryngoscopy and bronchoscopy can help visualize the airways to establish a definitive diagnosis. If the patient appears critically ill, then endotracheal intubation should be performed if the cause of stridor is thought to be from epiglottitis or bacterial tracheitis.
Management of stridor should be undertaken from the time of initial assessment in the critically ill-appearing patient. Specific treatment should be tailored to the underlying diagnosis. In general, the following precautions should be maintained when managing/treating stridor.
Differential diagnosis of stridor can include infectious, inflammatory, or anatomical etiologies. The emergency physician should always recognize croup, epiglottitis, anaphylaxis, bacterial tracheitis, abscess, and foreign aspiration as a cause of stridor. The differential can be narrowed down based on the patients presenting age and the duration of the stridor.
Given that the etiology of stridor is a robust, effective diagnosis and management of stridor relies on the clinical suspicion of the healthcare team, along with imaging modalities in unclear cases. Appropriate treatment then becomes directed toward the underlying cause and disease process. When a patient is presenting in extremis with stridor, it is up to the healthcare provider to rapidly recognize impending deterioration, gather the appropriate resources which many include rapid consultation with anesthesiology and appropriate surgical teams. In terms of croup, for instance, there have been many clinical trials demonstrating appropriate management based on the clinical presentation and clinical severity scores, which have led to decreased endotracheal intubations, as well as decreased hospital course length of stay, with the use of corticosteroids. [Level II] When the cause of stridor is in question, it is crucial to communicate effectively, and as quickly as possible with the entire healthcare team including nurses, pharmacists, and surgical staff to ensure proper management and provide the appropriate treatment for each patient.
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