Stridor is an abnormal, high-pitched sound produced by
turbulent airflow through a partially obstructed airway at the level
of the supraglottis, glottis, subglottis, and/or trachea.[1] The tonal
characteristics of the sound are extremely variable (ie, harsh,
musical, or breathy); however, combined with the phase, volume,
duration, rate of onset, and associated symptoms, the tonal
characteristic may provide additional diagnostic clues. Stridor is
a symptom, not a diagnosis or disease, and the underlying cause
must be determined. Stridor may be inspiratory, expiratory, or
biphasic depending on its timing in the respiratory cycle.
Inspiratory stridor suggests a laryngeal obstruction, while
expiratory stridor implies tracheobronchial obstruction. Biphasic
stridor suggests a subglottic or glottic anomaly. In addition to a
complete history and physical, as well as other possible additional
studies, most cases require flexible and/or rigid endoscopy to
adequately evaluate the etiology of stridor
History
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.

Place particular emphasis on the age of onset, duration,
severity, and progression of the stridor; precipitating events
(eg, crying, feeding); positioning (eg, prone, supine, sitting);
quality and nature of crying; presence of aphonia; and other





associated symptoms (eg, paroxysms of cough, aspiration,
difficulty feeding, drooling, sleep disordered breathing).[6]
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.
Past surgical history, particularly neck or cardiothoracic
surgeries, puts the recurrent laryngeal nerve at risk of injury
Obtain a detailed developmental history.
In addition, elicit history of color change, cyanosis,
respiratory effort, and apnea 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) that can cause laryngeal and
tracheal mucosal irritation that could lead to edema and
stridor.
Physical
On initial presentation, especially in patients with acute onset of
symptoms, immediately assess the child for severity of stridor and
respiratory compromise. Give special attention to the heart and
respiratory rates, cyanosis, use of accessory muscles of respiration,
nasal flaring, level of consciousness, and responsiveness.


If distress is moderate to severe, further physical examination
should be deferred until the patient reaches a facility
equipped for emergent 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.
Note the presence of infection in the oral cavity; crepitations
or masses in the soft tissues of the face, neck, or chest; and
deviation of the trachea.
Use care when examining (especially 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.
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, give special attention to craniofacial morphology,
patency of the nares, and cutaneous hemangiomas. Growth
parameters are very helpful, especially in evaluation of
chronic stridor
Causes
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.
Aspiration of foreign body is common in children aged 1-2
years. Usually, foreign bodies are food such as nuts, hot dogs,
popcorn, and hard candy that is inhaled. A history of coughing and
choking that precedes development of respiratory symptoms may
be present.
Bacterial tracheitis is relatively uncommon and mainly
affects children younger than 3 years. It is a secondary infection
(most commonly due to Staphylococcus aureus) following a viral
process (commonly croup or influenza).
Retropharyngeal abscess is a complication of bacterial
pharyngitis 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.
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 swallowing or speaking.
Spasmodic croup, also termed acute spasmodic laryngitis,
occurs most commonly in children aged 1-3 years. Presentation
may be identical to 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, wheezing) that indicate the involvement of
other organs.
Epiglottitis is a medical emergency occurring 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 up
to 75% of all cases of stridor.Stridor may be exacerbated by crying
or feeding. Placing the patient in a prone position with the head up
improves the stridor; supine position worsens the stridor.
Laryngomalacia is usually benign and self-limiting and improves
as the child reaches age 1 year. If significant obstruction or lack of
weight gain is present, surgical correction or supraglottoplasty may
be considered if there are observed tight mucosal bands holding the
epiglottis close to the true vocal cords or redundant mucosa
overlying the arytenoids.]
It should be kept in mind that the presentation of laryngomalacia in
older children (late-onset laryngomalacia) can differ from that of
congenital laryngomalacia.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 articles on glottic and
subglottic stenosis).
Vocal cord dysfunction is likely the second most common
cause of stridor in infants. Unilateral vocal cord paralysis can be
congenital or secondary to birth or surgical trauma, such as
cardiothoracic surgery. 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. It 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.
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.
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. Medical or
surgical intervention is based on the severity of symptoms.
Treatment options consist of oral steroids, intralesion steroids,
laser therapy with CO2 or potassium-titanyl-phosphate (KTP)
lasers, or surgical resection. Oral propranolol has been proven to
be an effective medical treatment in the appropriate population
(contraindicated in children with severe asthma, diabetes, or heart
disease).
Laryngeal papillomas occur secondary to vertical transmission of
the human papilloma virus 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.[18]
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 is the most common cause of expiratory
stridor. It is caused by a defect on the cartilage resulting in the loss
of rigidity necessary to maintain the tracheal lumen patent or by an
extrinsic compression of the trachea.
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 requires
surgery based on severity of symptoms. 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.
Differential Diagnoses






Congenital Arterial and Venous Anomalies: Surgical
Perspective
Congenital Stridor
Gastroesophageal Reflux
Laryngomalacia
Subglottic Stenosis
Tracheomalacia
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 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 to evaluate the airway and lungs.
High-kilovoltage, short-exposure, endolateral airway
radiographs (useful to demonstrate upper airway structures)
or inspiratory and expiratory or lateral decubitus radiographs
to demonstrate air trapping may be used to supplement AP
and lateral radiographs.
Barium esophagram may be performed if vascular
compression, tracheoesophageal fistula, GER, or
neurological dysfunction is suspected.
Contrast-enhanced CT scanning can demonstrate mediastinal
masses or aberrant vessels.
An 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.
Other Tests


Pulmonary function testing may be useful to differentiate
restrictive and obstructive lung processes and to define
whether the obstruction is in the upper or lower airway.
Polysomnography may be required under certain
circumstances, especially if history suggests obstructive sleep
apnea.
Procedures


The key to defining stridor of all phases is to look at the
airway. Direct laryngoscopy and bronchoscopy is the
criterion standard for making a diagnosis in infants and
children with stridor.
In children with stable oxygen saturations and in whom
findings on a lateral neck radiograph or the clinical picture
does not indicate acute epiglottitis, the initial procedure to
evaluate stridor should be a flexible laryngoscopy performed
by an otolaryngologist in the clinic with topical
vasoconstrictor and/or topical anesthetic as needed. The
status of the larynx can be addressed, looking for
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, or,
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.
Medical Care
The treatment of stridor must be tailored according to the
underlying or predisposing condition. Emergent management
consists of ensuring that the airway is adequate. If not, appropriate
resuscitative measures must be initiated. Some conditions (eg,
epiglottitis, bacterial tracheitis) may require antibiotics, while
steroids may be useful in other situations.
Surgical Care
Certain conditions, such as severe laryngomalacia, laryngeal
stenosis, critical tracheal stenosis, laryngeal and tracheal tumors
and lesions (eg, laryngeal papillomas, hemangiomas, others), and
foreign body aspiration, require surgical correction. 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 emergent basis. Please see relevant
articles for specific management
Diet
Patients with moderate to severe stridor should be given nothing by
mouth (NPO) in preparation for possible intubation, laryngoscopy,
bronchoscopy, and tracheotomy.
croup
History
Croup usually begins with nonspecific respiratory symptoms (ie,
rhinorrhea, sore throat, cough). Fever is generally low grade (3839°C) but can exceed 40°C. Within 1-2 days, the characteristic
signs of hoarseness, barking cough, and inspiratory stridor
develop, often suddenly, along with a variable degree of
respiratory distress. Symptoms are perceived as worsening at night,
with most ED visits occurring between 10 pm and 4 am.
Symptoms typically resolve within 3-7 days but can last as long as
2 weeks.
Spasmodic croup (recurrent croup) typically presents at night with
the sudden onset of "croupy" cough and stridor. The child may
have had mild upper respiratory complaints prior to this, but more
often has behaved and appeared completely well prior to the onset
of symptoms. Allergic factors may cause recurrent croup due to
respiratory epithelial changes from the viral infection.
Another diagnostic consideration is gastroesophageal reflux
(GER). Studies of children presenting with recurrent croup have
reported relief of their respiratory symptoms when treated for
reflux.[13] .
2
Background
Croup is a common, primarily pediatric viral respiratory tract
illness. As its alternative names, laryngotracheitis and
laryngotracheobronchitis, indicate, croup generally affects the
larynx and trachea, although this illness may also extend to the
bronchi. It is the most common etiology for hoarseness, cough, and
onset of acute stridor in febrile children. Symptoms of coryza may
be absent, mild, or marked. The vast majority of children with
croup recover without consequences or sequelae; however, it can
be life-threatening in young infants.

Croup manifests as hoarseness, a seal-like barking cough,
inspiratory stridor, and a variable degree of respiratory
distress. However, morbidity is secondary to narrowing of
the larynx and trachea below the level of the glottis
(subglottic region)
Child with croup. Note the steeple or pencil
sign of the proximal trachea evident on this anteroposterior film.
Courtesy of Dr. Kelly Marshall, CHOA at Scottish Rite.
Young infants who present with stridor require a meticulous
evaluation to determine the etiology and, most importantly, to
exclude rare life-threatening causes. Although croup is usually a
mild, self-limited disease, upper airway obstruction may result in
respiratory distress and even death.
Etiology
Viruses causing acute infectious croup are spread through either
direct inhalation from a cough and/or sneeze or by contamination
of hands from contact with fomites, with subsequent touching the
mucosa of the eyes, nose, and/or mouth. The most common viral
etiologies are parainfluenza viruses. The type of parainfluenza (1,
2, and 3) causing outbreaks varies each year.
The primary ports of entry are the nose and nasopharynx. The
infection spreads and eventually involves the larynx and trachea.
Although the lower respiratory tract may also be affected, some
practitioners consider laryngotracheobronchitis a separate entity,
with bacterial secondary infection as the potential cause..
Spasmodic croup (laryngismus stridulus) is a noninfectious
variant of the disorder, with a clinical presentation similar to that
of the acute disease but with less coryza. This type of croup always
occurs at night and has the hallmark of reoccurring in children;
hence it has also been called “recurrent croup.” In spasmodic
croup, subglottic edema occurs without the inflammation typical in
viral disease. Although viral illnesses may trigger this variant, the
reaction may be of allergic etiology rather than a direct result of an
infectious process.
Causes
Parainfluenza viruses (types 1, 2, 3) are responsible for as many as
80% of croup cases, with parainfluenza types 1 and 2, accounting
for nearly 66% of cases. Type 3 parainfluenza virus causes
bronchiolitis and pneumonia in young infants and children. Type 4,
with subtypes 4A and 4B, are not as well understood and tend to be
associated with milder clinical illness.
Influenza A is associated with severe respiratory disease as it has
been detected in children with marked respiratory compromise.
The bacterial pathogen, Mycoplasma pneumoniae, has also been
identified in a few cases of croup.[5] Prior to 1970, diphtheria was a
common cause of crouplike symptoms. The vaccine has eliminated
this infection with no cases reported in the United States in over 20
Differential Diagnoses










Airway Foreign Body
Bacterial Tracheitis
Diphtheria
Epiglottitis
Inhalation Injury
Laryngeal Fractures
Laryngomalacia
Measles
Mononucleosis and Epstein-Barr Virus Infection
Peritonsillar Abscess
Approach Considerations
Urgent care or emergency department treatment of croup depends
on the degree of respiratory distress. In mild croup, a child may
present with only a croupy cough and may require nothing more
than parental reassurance, given alertness, baseline minimal
respiratory distress, proper oxygenation, and stable fluid status.
The caregivers may only need education regarding the course of
the disease and supportive homecare guidelines.
However, any infant/child who presents with significant
respiratory distress/complaints with stridor at rest must have a
thorough clinical evaluation to ensure the patency of the airway
and maintenance of effective oxygenation and ventilation. Keep
young children as comfortable as possible, allowing him or her to
remain in a parent's arms and avoiding unnecessary painful
interventions that may cause agitation, respiratory distress, and
lead to increased oxygen requirements. Persistent crying increases
oxygen demands, and respiratory muscle fatigue can worsen the
obstruction.
Concurrently, careful monitoring of the heart rate (for tachycardia),
respiratory rate (for tachypnea), respiratory mechanics (for sternal
wall retractions), and pulse oximetry (for hypoxia) are important.
Assessment of the patient’s hydration status, given the risk of
increased insensible losses from fever and tachypnea, along with a
history of decreased oral intake, is also imperative.
Infants and children with severe respiratory distress or compromise
may require 100% oxygenation with ventilation support, initially
with a bag-valve-mask device. If the airway and breathing require
further stabilization due to increasing respiratory fatigue and
hence, worsening hypercarbia, (as evident by ABG) the patient
should be intubated with an endotracheal tube. Intubation should
be accomplished with an endotracheal tube that is 0.5-1 mm
smaller than predicted. Once airway stabilization is achieved, these
patients are transferred for their ongoing care to a pediatric
intensive care unit.
The current cornerstones of treatment in the urgent care
clinics or emergency departments are corticosteroids and
nebulized epinephrine; steroids have proven beneficial in
severe, moderate, and even mild croup.[22] In the
straightforward cases of croup, antibiotics are not prescribed,
as the primary cause is viral. Lack of improvement or
worsening of symptoms can be due to a secondary bacterial
process, which would require the use of antimicrobials for
treatment. Typically, these patients initially would have had
moderate-to-severe croup scores, requiring inpatient care and
observation.
Corticosteroids
Corticosteroids are beneficial due to their anti-inflammatory
action, whereby laryngeal mucosal edema is decreased. They also
decrease the need for salvage nebulized epinephrine.
Corticosteroids may be warranted even in those children who
present with mild symptoms. Treatment of croup with
corticosteroids has not shown significant adverse effects; however
despite the low risk, their use should be carefully evaluated for
children with diabetes, an underlying immunocompromised state,
or those recently exposed to or diagnosed with varicella or
tuberculosis, due to the potential risk of exacerbating the systemic
disease process.
A single dose of dexamethasone has been shown to be effective in
reducing the overall severity of croup, if administered within the
first 4-24 hours after the onset of illness. The long half-life of
dexamethasone (36-54 h) often allows for a single injection or dose
to cover the usual symptom duration. Studies have shown that
dexamethasone dosed at 0.15 mg/kg is as effective as 0.3 mg/kg or
0.6 mg/kg (with a maximum daily dose of 10 mg) in relieving the
symptoms of mild-to-moderate croup. Despite this knowledge,
clinicians still tend to favor the dose of 0.6 mg/kg for initial
treatment of croup. This dosage, in fact, is more effective for
patients diagnosed with severe croup and remains the optimal
amount for safety, benefit and cost-effectiveness.[33, 34]
Dexamethasone has shown the same efficacy if administered
intravenously, intramuscularly, or orally.[35] The route of
administration is patient-dependent as based on the patient’s age,
ability to tolerate orals, an severity of presenting illness. The use of
inhaled corticosteroids (budesonide) with systemic treatment does
not provide additional benefit.[36]
Patients given a single oral dose of prednisolone (1 mg/kg) were
found to have made more return visits than did those who received
a single oral dose of dexamethasone (0.15 mg/kg).[37] This is due to
the lesser potency to reduce inflammation and shortened half-life
of prednisolone (18-36 h) when compared with
ble inspiratory stridor (see the image below).
Cool mist administration
Throughout the 19th and most of the 20th century, cool mist
administration was the mainstay of treatment. Hospitals had "croup
rooms" filled with cool mist. Theoretically, mist moistens airway
secretions, decreases their viscosity, and soothes the inflamed
mucosa. Animal data show that microaerosol inhalation activates
mechanoreceptors that produce a reflex slowing of respiratory flow
rate and leads to improved airflow.
However, despite its continued widespread use, little evidence
supports the clinical efficacy of cool mist or humidification
therapy. Randomized studies of children with moderate-to-severe
croup revealed no difference in outcome between those who
received cool mist and those who did not.[23] Mist tents, used in the
hospital setting, can disperse fungus and molds if not properly
cleaned.
More importantly, the tents separate the child from the parent by
creating a “plastic barrier," causing anxiety and agitation,
potentially worsening the child’s symptoms and hindering ongoing
clinical assessment.[24, 25, 26] In the home, vaporizers (heated
humidification) producing hot steam to moisten the air should not
be used because of the risk of scalding or burns.[27]
Epinephrine
Nebulized racemic epinephrine is a 1:1 mixture of dextro (D)
isomers and levo (L) isomers of epinephrine with the L form (Lepinephrine) as the active component. Its use is typically reserved
for patients in the hospital setting with moderate-to-severe
respiratory distress. Epinephrine works by adrenergic stimulation,
which causes constriction of the precapillary arterioles, thereby
decreasing capillary hydrostatic pressure. This leads to fluid
resorption from the interstitium and improvement in the laryngeal
mucosal edema.[22] Epinephrine’s beta2-adrenergic activity leads to
bronchial smooth muscle relaxation and bronchodilation. Its
effectiveness is immediate with evidence of therapeutic benefit
within the first 30 minutes and then, lasts from 90-120 minutes
(1.5-2 h).
Patients who receive nebulized racemic epinephrine in the
emergency department should be observed for at least 3 hours post
last treatment because of concerns for a return of bronchospasm,
worsening respiratory distress, and/or persistent tachycardia.
Patients can be discharged home only if they demonstrate healthy
color, good air entry, baseline consciousness, and no stridor at rest
and have received a dose of corticosteroids