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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.[rx]
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.
Causes of Stridor
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
- Nasal deformities such as choanal atresia, choanal atresia, septum deformities, turbinate hypertrophy, vestibular atresia, or vestibular stenosis
- Craniofacial anomalies such as Pierre Robin or Apert syndromes, or conditions causing macroglossia
- Laryngeal anomalies such as laryngomalacia, laryngeal webs, laryngeal cysts, laryngeal clefts, subglottic stenosis, vocal cord paralysis, tracheal stenosis, tracheomalacia
Noncongenital Causes of Stridor in Pediatrics
- Acute: Foreign body aspiration, airway burns, bacterial tracheitis, epiglottitis, anaphylaxis, croup.
- Subacute: Peritonsillar abscess, retropharyngeal abscess.
- Chronic: Vocal cord dysfunction, laryngeal spasm, neoplasm.
Most common cause of chronic stridor in infants is laryngomalacia.[rx]
Symptoms of Stridor
- Hives: Should prompt evaluation for anaphylaxis secondary to allergic trigger
- A cough: Typically presents with croup
- Drooling: Typically seen with retropharyngeal abscess and epiglottitis, or foreign body aspiration
Diagnosis of Stridor
- Neonates: Congenital abnormalities present within the first month of life, with some presenting later in life.
- Infants to toddlers: The most common cause in this age group is croup or foreign body aspiration.
- Young adolescents: Vocal cord dysfunction, peritonsillar abscess
- Acute: Epiglottitis, bacterial tracheitis will present with severe respiratory distress and secretions, and fever, if fever is not present then suspect foreign body aspiration or anaphylaxis
- Subacute: Croup will present with intermittent stridor
- General appearance: Assess for any swelling of soft tissues of the neck and oropharynx, and rashes or hives, or any clubbing of digits.
- HEENT: Assess tongue size, pharyngeal edema, or peritonsillar abscess. Be cautious in manipulating the oropharynx of a suspected epiglottitis patient, and consider doing this in a controlled setting such as the operating room.
- Lungs: Asses rate and depth of breathing, auscultate for inspiratory and expiratory stridor. Auscultate over the anterior neck to best hear stridor.[rx]
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.[rx]
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.
Treatment of Stridor
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.[rx]
- Avoid agitating child with stridor
- Monitor for rapid deterioration due to respiratory failure
- Avoid direct examination or manipulation of the pharynx (if epiglottitis is suspected). In such situations, securing the airway takes precedence over diagnostic evaluation.
- Skilled personnel in airway management should accompany the patient at all times. Further evaluation should be performed where definitive airway management can be achieved in a controlled environment such as the operating room.
- Consider foreign body aspirations if symptoms develop acutely such as sudden coughing and choking in a previously healthy child.
- Avoid beta-agonists in croup; they are a possible risk of worsening upper airway obstruction.