Updated: Apr 07, 2022
Author: Brian E Benson, MD, FACS; Chief Editor: Ravindhra G Elluru, MD, PhD 


Practice Essentials

Stridor is an abnormal, high-pitched sound produced by turbulent airflow through a partially obstructed airway at the level of the supraglottis, glottis, subglottis, or trachea.[1]  Its tonal characteristics are extremely variable (ie, harsh, musical, or breathy); however, when combined with the phase, volume, duration, rate of onset, and associated symptoms, the tonal characteristics of the sound may provide additional diagnostic clues.

In all cases, stridor should be differentiated from stertor, which is a lower-pitched, snoring-type sound generated at the level of the nasopharynx, oropharynx, and, occasionally, supraglottis.

Stridor is a symptom, not a diagnosis or a disease, and the underlying cause must be determined. It may be inspiratory (most common), expiratory, or biphasic, depending on its timing in the respiratory cycle, and the three forms each suggest different causes, as follows:

  • Inspiratory stridor suggests a laryngeal obstruction
  • Expiratory stridor implies tracheobronchial obstruction
  • Biphasic stridor suggests a subglottic or glottic anomaly

In most cases of stridor, besides a complete history and physical examination, along with other possible additional studies, flexible or rigid endoscopy is required for an adequate evaluation of the etiology.

The treatment of stridor must be tailored according to the particular underlying or predisposing condition present (see Treatment).


Gases produce pressure equally in all directions; however, when a gas moves in a linear direction, it produces pressure in the forward vector and decreases the lateral pressure. When air passes through a narrowed flexible airway in a child, the lateral pressure that holds the airway open can drop precipitously (the Bernoulli principle) and cause the tube to close. This process obstructs airflow and produces stridor.

Stridor may result from lesions involving the central nervous system (CNS), the cardiovascular system, the gastrointestinal (GI) tract, or the respiratory tract.


Acute stridor

Laryngotracheobronchitis, commonly known as croup, is the most common cause of acute stridor in children aged 6 months to 2 years. The patient has a barking cough that is worse at night and may have low-grade fever.[2, 3]

Aspiration of foreign body is common in children aged 1-2 years. Usually, foreign bodies are food (eg,nuts, hot dogs, popcorn, or hard candy) that is inhaled. A history of coughing and choking that precedes development of respiratory symptoms may be present.[4]

Bacterial tracheitis is relatively uncommon and mainly affects children younger than 3 years. It is a secondary infection (most commonly due to Staphylococcus aureus) that follows a viral process (commonly croup or influenza).

Retropharyngeal abscess is a complication of bacterial pharyngitis that is observed in children younger than 6 years. The patient presents with abrupt onset of high fevers, difficulty swallowing, refusal to feed, sore throat, hyperextension of the neck, and respiratory distress.[5]

Peritonsillar abscess is an infection in the potential space between the superior constrictor muscles and the tonsil. It is common in adolescents and preadolescents. The patient develops severe throat pain, trismus, and trouble with swallowing or speaking.

Spasmodic croup, also termed acute spasmodic laryngitis, occurs most commonly in children aged 1-3 years. The presentation may be identical to that of croup.

Allergic reaction (ie, anaphylaxis) occurs within 30 minutes of an adverse exposure. Hoarseness and inspiratory stridor may be accompanied by symptoms (eg, dysphagia, nasal congestion, itching eyes, sneezing, and wheezing) that indicate the involvement of other organs.

Epiglottitis is a medical emergency that occurs most commonly in children aged 2-7 years. Clinically, the patient experiences an abrupt onset of high-grade fever, sore throat, dysphagia, and drooling.

Chronic stridor

Laryngomalacia is the most common cause of inspiratory stridor in the neonatal period and early infancy and accounts for as many as 75% of all cases of stridor.[6] Stridor may be exacerbated by crying or feeding. Placing the patient in a prone position with the head up alleviates the stridor; a supine position exacerbates the stridor.

Laryngomalacia is usually benign and self-limiting and improves as the child reaches age 1 year. In cases where significant obstruction or lack of weight gain is present, surgical correction or supraglottoplasty may be considered if the clinician has observed tight mucosal bands holding the epiglottis close to the true vocal cords or redundant mucosa overlying the arytenoids.[7]

It should be kept in mind that the presentation of laryngomalacia in older children (late-onset laryngomalacia) can differ from that of congenital laryngomalacia.[8] Possible manifestations of late-onset laryngomalacia include obstructive sleep apnea syndrome, exercise-induced stridor, and even dysphagia. Supraglottoplasty can be an effective treatment option.

Patients with subglottic stenosis can present with inspiratory or biphasic stridor. Symptoms can be evident at any time during the first few years of life. If symptoms are not present in the neonatal period, this condition may be misdiagnosed as asthma. Congenital subglottic stenosis occurs when an incomplete canalization of the subglottis and cricoid rings causes a narrowing of the subglottic lumen. Acquired stenosis is most commonly caused by prolonged intubation (see also Glottic Stenosis).

Vocal cord dysfunction is probably the second most common cause of stridor in infants. Unilateral vocal cord paralysis can be either congenital or secondary to birth or surgical trauma (eg, from cardiothoracic procedures). Patients with a unilateral vocal cord paralysis present with a weak cry and biphasic stridor that is louder when awake and improves when lying with the affected side down.

Bilateral vocal cord paralysis is a more serious entity. Patients usually present with aphonia and a high-pitched biphasic stridor that may progress to severe respiratory distress. This condition is usually associated with CNS abnormalities, such as Arnold-Chiari malformation or increased intracranial pressure. Vocal cord paralysis in infants usually resolves within 24 months.

Laryngeal dyskinesia, exercise-induced laryngomalacia, and paradoxical vocal cord motion are other neuromuscular disorders that may be considered.

Laryngeal webs are caused by an incomplete recanalization of the laryngeal lumen during embryogenesis. Most (75%) are in the glottic area. Infants with laryngeal webs have a weak cry and biphasic stridor. Intervention is recommended in the setting of significant obstruction and includes cold knife or CO2 laser ablation.[9] (See Congenital Malformations of the Larynx.)

Laryngeal cysts are a less frequent cause of stridor. They are usually found in the supraglottic region in the epiglottic folds. Patients may present with stridor, hoarse voice, or aphonia. Cysts may cause obstruction of the airway lumen if they are very large. (See Congenital Malformations of the Larynx.)

Laryngeal hemangiomas (glottic or subglottic) are rare, and half of them are accompanied by cutaneous hemangiomas in the head and neck. Patients usually present with inspiratory or biphasic stridor that may worsen as the hemangioma enlarges. Typically, hemangiomas present in the first 3-6 months of life during the proliferative phase and regress by age 12-18 months. (See Congenital Malformations of the Larynx.)

Medical or surgical intervention for laryngeal hemangiomas is based on the severity of symptoms. Treatment options consist of oral steroids, intralesional steroids, laser therapy with CO2 or potassium-titanyl-phosphate (KTP) lasers, and surgical resection. Oral propranolol has proved to be an effective medical treatment in the appropriate population (it is contraindicated in children with severe asthma, diabetes, or heart disease).[10]

Laryngeal papillomas occur secondary to vertical transmission of the human papillomavirus from maternal condylomata or infected vaginal cells to the pharynx or larynx of the infant during the birth process. These are primarily treated with surgical excision, with questionable use of cidofovir and interferon in refractory cases.[11] A high rate of recurrence of disease is noted, with a need for multiple surgical debridements and a small risk of malignancy (5% malignant degeneration).

Tracheomalacia, if present in the proximal (extrathoracic) trachea, can be associated with inspiratory stridor. If it is present in the distal (intrathoracic) trachea, it is associated more with expiratory noise. Tracheomalacia is caused either by a defect on the cartilage, resulting in loss of the rigidity necessary to keep the tracheal lumen patent, or by an extrinsic compression of the trachea.

Stenosis of the proximal trachea can cause stridor. Tracheal stenosis can be congenital or secondary to extrinsic compression. Congenital stenosis is usually related to complete tracheal rings, is characterized by a persistent stridor, and necessitates surgery based on symptom severity.

The most common extrinsic causes of stenosis include vascular rings, slings, and a double aortic arch that encircles the trachea and esophagus. Pulmonary artery slings are also associated with complete tracheal rings. External compression can also result in tracheomalacia. Patients usually present during the first year of life with noisy breathing, intercostal retractions, and a prolonged expiratory phase.




The most common presenting symptom is loud, raspy, noisy breathing. The caretaker may interpret this symptom as wheezing or even as a severe upper respiratory tract infection. Depending on the underlying etiology, the presentation may be acute or chronic and may be accompanied by other symptoms. If symptoms are not observed in the office, especially when they are present only at night, having parents make a tape recording, preferably even videotaping, can provide useful information.

A thorough history may provide helpful clues to the underlying etiology of stridor.[12, 13] Particular emphasis should be placed on the following:

  • Age of onset, duration, severity, and progression of the stridor
  • Precipitating events (eg, crying or feeding)
  • Positioning (eg, prone, supine, or sitting)
  • Quality and nature of crying
  • Presence of aphonia
  • Other associated symptoms (eg, paroxysms of cough, aspiration, difficulty in feeding, drooling, or sleep-disordered breathing) [14]

A perinatal history is especially important and should include direct questioning regarding maternal condylomata, type of delivery (including shoulder dystocia), endotracheal intubation use and duration, and presence of congenital anomalies. A surgical history should be obtained; previous surgical treatment, particularly if it includes neck or cardiothoracic procedures, puts the recurrent laryngeal nerve at risk for injury.[15]

A detailed developmental history should be obtained. In addition, a history of color change, cyanosis, respiratory effort, and apnea should be elicited to determine the severity of stridor. A feeding and growth history should be evaluated because significant airway obstruction can lead to caloric waste, resulting in lack of weight gain and growth. Additionally, regurgitation and spitting up could be a sign of gastroesophageal reflux (GER), which can cause laryngeal and tracheal mucosal irritation that could lead to edema and stridor.[16]

Physical Examination

On initial presentation, especially if the symptoms are of acute onset, the child should immediately be assessed for severity of stridor and respiratory compromise. Special attention should be paid to the following:

  • Heart and respiratory rates
  • Cyanosis
  • Use of accessory muscles of respiration
  • Nasal flaring
  • Level of consciousness
  • Responsiveness

If distress is moderate to severe, further physical examination should be deferred until the patient reaches a facility equipped for emergency management of the pediatric airway. Physical examination of a patient with suspected acute epiglottitis is contraindicated. The patient may prefer certain positions that alleviate the stridor.

The following, if present, should be noted:

  • Infection in the oral cavity
  • Crepitations or masses in the soft tissues of the face, neck, or chest
  • Deviation of the trachea

Care must be exercised in examining (and especially in palpating) the oral cavity or pharynx because sudden dislodgement of a foreign body or rupture of an abscess can cause further airway compromise. Drooling from the mouth suggests poor handling of secretions.

It is important to observe the character of the cough, cry, and voice.

The presence of fever and toxicity generally implies serious bacterial infections.

Careful auscultation of the nose, oropharynx, neck, and chest helps to discern the location of the stridor.

In infants, special attention should be paid to craniofacial morphology, patency of the nares, and cutaneous hemangiomas. Growth parameters are helpful, especially in the evaluation of chronic stridor.





Laboratory Studies

On initial evaluation, pulse oximetry may be useful to determine the extent and severity of the stridor and respiratory compromise. For moderate-to-severe cases, arterial blood gas evaluation may be needed.

Other laboratory evaluations may be performed as dictated by the clinical situation. Generally, no investigations are required for mild stridor.

Imaging Studies

Anteroposterior (AP) and lateral radiographs of the neck and chest are useful for evaluating the airway and lungs. These radiographs may be supplemented by high-kilovoltage, short-exposure endolateral airway radiographs (useful for demonstrating upper airway structures) or inspiratory and expiratory or lateral decubitus radiographs (useful for demonstrating air trapping).

Barium esophagography may be performed if vascular compression, tracheoesophageal fistula, gastroesophageal reflux (GER), or neurologic dysfunction is suspected.

Contrast-enhanced computed tomography (CT) can demonstrate mediastinal masses or aberrant vessels. Magnetic resonance imaging (MRI) may be helpful in delineating lesions of the upper airway and vascular anomalies.

If GER is suspected, a pH probe or barium swallow may be performed to support the diagnosis.

Laryngoscopy and Bronchoscopy

The key to defining stridor of all phases is to evaluate the airway directly. Direct laryngoscopy with bronchoscopy is the criterion standard for making a diagnosis in infants and children with stridor.

If the child's oxygen saturations are stable and neither the findings on lateral neck radiography nor the clinical picture is indicative of acute epiglottitis, the initial procedure for evaluating stridor should be a flexible laryngoscopy performed by an otolaryngologist in the clinic with a topical vasoconstrictor, a topical anesthetic, or both as needed. The status of the larynx can be addressed, with an eye to abnormalities such as laryngomalacia, true vocal cord paresis or paralysis, laryngeal tumors or cysts, or signs and symptoms of GER.

Often, a good evaluation is possible; occasionally, only a glimpse of the subglottis is observed, which may help direct further evaluation, such as a formal direct laryngoscopy and bronchoscopy in the operating room.

Other Tests

Pulmonary function testing may be helpful in differentiating restrictive and obstructive lung processes and defining whether the obstruction is in the upper or lower airway.

Polysomnography may be required under certain circumstances, especially if the history suggests obstructive sleep apnea.



Medical Care

The treatment of stridor must be tailored according to the particular underlying or predisposing condition present (see Etiology). Emergency management consists of ensuring that the airway is adequate. If it is not, appropriate resuscitative measures must be initiated. For some conditions (eg, epiglottitis and bacterial tracheitis), antibiotic therapy may be required, whereas in other scenarios, steroid therapy may be useful.[17, 18]

Surgical Care

For certain conditions, such as the following, surgical correction is required:

  • Severe laryngomalacia
  • Laryngeal stenosis
  • Critical tracheal stenosis
  • Laryngeal and tracheal tumors and lesions (eg, laryngeal papillomas and hemangiomas)
  • Foreign body aspiration

Occasionally, tracheotomy is used to protect the airway to bypass laryngeal abnormalities and stent or bypass tracheal abnormalities. Other conditions, such as retropharyngeal and peritonsillar abscess, may have to be dealt with on an emergency basis.


Patients with moderate to severe stridor should be given nothing by mouth (nil per os [NPO]) in preparation for possible intubation, laryngoscopy, bronchoscopy, and tracheotomy.

Long-Term Monitoring

Close clinical follow-up is important, especially in patients with congenital anomalies (eg, laryngomalacia, laryngeal webs, and vocal cord paresis), to follow disease progression.




Dexamethasone (Baycadron, Decadron, Dexamethasone Intensol)

Prednisone (Deltasone, Prednisone Intensol, Rayos)

Alpha/Beta Adrenergic Agonists

Epinephrine (Adrenaclick, Adrenalin, Auvi-Q)


Questions & Answers


What is stridor?

What is the pathophysiology of stridor?

What are the most common causes of acute stridor?

What is the role of bacterial tracheitis in the etiology of stridor?

What are symptoms of retropharyngeal abscess-related stridor?

What are symptoms of peritonsillar abscess-related stridor?

What are the symptoms of spasmodic croup-related stridor?

How are allergic reactions manifested in patients with stridor?

What are the symptoms of epiglottitis in stridor?

What is the most common cause of inspiratory stridor?

What is the role of subglottic stenosis in the etiology of stridor?

What is the second most common cause of stridor?

What is the role of neuromuscular disorders in the etiology of stridor?

How is tracheomalacia related to stridor?

How does stenosis of the proximal trachea cause stridor?


What are the signs and symptoms of stridor?

What should be the focus of history in the evaluation of stridor?

What should be assessed in the physical exam for stridor?

Which physical findings are characteristic of stridor?


What are the differential diagnoses for Stridor?


What is the role of lab studies in the evaluation of stridor?

What is the role of imaging studies in the evaluation for stridor?

What is the role of laryngoscopy and bronchoscopy in the diagnosis of stridor?

What is the role of pulmonary function testing and polysomnography in the diagnosis of stridor?


What is included in the emergency management of stridor?

When is surgery indicated for stridor?

What dietary restrictions are needed during the treatment of stridor?

What is goal of long-term monitoring of patients with stridor?


Which medications in the drug class Alpha/Beta Adrenergic Agonists are used in the treatment of Stridor?

Which medications in the drug class Corticosteroids are used in the treatment of Stridor?