Stridor in children
Balasubramanian M.S. D.L.O.
Definition: Stridor is an auditory manifestation of a
disordered respiratory function. In simple terms it could be termed
as noisy breathing. It should be borne in mind that not all noisy
breathing is stridor. Voluntary or involuntary vocalisations, moist
sounds such as bubbling of secretions in the larynx or pharynx are
to be excluded.
There is one more noisy breathing known as stertor,
derived from the latin word stertere meaning to snore. This is
caused by obstruction of airway above the level of the larynx. It is
low pitched snoring or snuffly sound produced by vibrations of
tissue of the naso pharynx, pharynx or soft palate. Stridor on the
other hand is caused due to air flow changes within the larynx,
trachea or bronchi. Stridor is infact more often musical in
character. The frequency of sound produced also ranges from lwo
pitched to high pitched frequencies.
Aerodynamic explanation of stridor and
Stridor and stertor are both due to turbulence of the air
flow within a partially obstructed respiratory tract. In order to
understand its mechanism we will have to go back to the physics of
airflow. According to Bedrnoulli's theorem if air passes through a
tube which has constrictions, the velocity of gas increases at the
level of the narrowing, and in order to preserve the law of
conservation of energy, the local gas pressure falls. The same
principle can be applied to air flowing through the respiratory
tract, which is flaccid and compressible in a child. There is a
natural increase in the pressure gradiant at the sites of
constriction, resulting in a collapse of the airway and temporary
cessation of airflow. Now Pascal's principle come into play, which
states that in fluid / gas at rest the pressure changes in one part
is transmitted without loss to every portion of the fluid or gas and
to the walls of the container. In addition to this the resilence of
the cartilagenous support of the airway in children cause the airway
to spring open thus resuming the air flow. Thus the fluttering
vibrations caused are amplified by the various resonators giving
rise to audible sounds which are known as either a stridor or a
Stertor is always inspiratory in its timing and has a low
frequency, where as a stridor can occur both during inspiration or
expiration with varying frequencies. Caution should be exercised
while applying these criteria to differentiate stridor from stertor
because there can always be a overlap between these
1. During inspiration, the relatively supple, poorly
supported structures of the infantile supraglottis tend to be drawn
into the glottic aperture due to the pressure differential that
exist between the pharynx and trachea during inspiration, on the
contrary expiration forces the prolapsed tissues out of the
laryngeal inlet. The noise caused by this process is limited to the
inspiratory phase and is often low pitched in character. Stridor of
this type occur in laryngomalacia.
2. In smaller bronchi and bronchioles, during expiration
there is accentuation of bronchial muscle contraction combined with
high velocity gas flow cause collapse of the airway causing stridor
during expiratory phase, it could be heard as a wheeze. This is
commonly caused by retained secretions or foreign
3. The relatively rigid walls of rima glottis and trachea
prevent collapse and hence stridor arising from these areas is due
to turbulance of airflow alone. If the obstruction is severe to and
fro stridor can occur (biphasic).
The associated signs / symptoms associated with stridor
1. Dyspnoea: Occurs in all patients with airway
obstruction. It is also associated with other signs like flaring of
the nostrils, use of accessory muscles of respiration, and cyanosis
may also be present in extreme cases. During obstruction an
extraordinarily high negative pressure causing indrawing of soft
tissues in the subcostal, intercostal, suprasternal and substernal
areas. Severe indrawing of the suprasternal area may cause a
phenomenon known as the tracheal tug, where the trachea appears to
be pulled down into the chest with each inspiration. In infants
& neonates who have a soft compliant chest wall the indrawing of
the subcostal space may be a normal phenomenon. Similarly these
signs of distress may not be seen in infants even during chronic
severe airway obstruction.
The respiratory obstruction which produces stridor &
stertor can lead to hypoxia, hypercapnia, pulmonary oedema, cor
pulmonale, vomiting, aspiration & pneumonia.
2. Cough : Is usually harsh and barking in nature. This
symptom is commonly associated with subglottic inflammation or
3. Hoarseness : Suggests laryngeal inflammation, trauma,
tumors or vocal cord mobility problems. In a child with stretor
there will not be any hoarseness of voice but the cry is usually
4. Deglutition : The process of deglutition &
respiration share the common pathway i.e. the oropharynx. Hence
disorders of swallowing may affect breathing and the vice versa is
showing the differences between stridor &
History : As with anyother disease a good history is a must for
accurate diagnosis of the etilogy of infantile stridor. History
should concentrate on the duration of the respiratory distress,
Positional variations if any, associated problems with feeding,
voice changes, and other congential abnormalities. In addition h/o
trauma or ingestion of foreign body is a must.
Causes of stridor are anatomically classified:
1. Supralaryngeal causes:
a. Nose - choanal atresia
Obstruction due to infection / truama / tubes
b. Cranio facial anamolies:
These patients have narrowing of oropharynx, nasopharynx and
nasal cavities. The may also additionally manifest with
macroglossia. The various anamolies associated with respiratory
Pierre Robin syndrome
Treacher collin syndrome
c. Macroglossia :
Beckwith Wiedemann syndrome
e. Laryngomalacia : Is caused by an excessiely elastic
cartilagenous support to the airway seen in infants. This commonly
affects the glottic and supra glottic airway of infants. This
excessively soft and elastic cartilage causes inspiratory collapse
of the arytenoid, aryepiglottic folds and epiglottis during
inspiration. The omega shaped epiglottis seen often in the infants
adds to the problem. This causes occlusion of the laryngeal inlet.
These patients have inspiratory stridor which becomes better on
prone position or when the child is calm. Stridor is worsened if the
child is restless or excited.
The cry of the child is usually normal. The child may also have
aspiration and feeding difficulties. It is commonly seen during the
first few months of life.
Direct laryngoscopy shows indrawing and falling forwards of the
arytenoid and the aryepiglottic folds. The epiglottis may be
This condition may be managed conservatively, as the cartilage in
infants tend to become stiffer as the child grows. In difficult
cases the patient may be subjected to tracheostomy to secure the
airway and to prevent aspiration, and feeding gastrostomy to
maintain the nutritional status of the child. Epiglottoplasty may be
considered in resistant cases.
2. Glottic causes:
a. Vocal cord palsy : Is one of the commonest cause of airway
obstruction. In 80% of patients it is unilateral.
Etiology: Could be caused due to injury to vagus nerve at the
level of Nucleus ambiguus - it is often bilateral.
Injury to the left recurrent laryngeal nerve due to cardio
vascular causes and thoracic causes.
It could be caused due to increased intracranial pressure - i.e.
Meningomyelocoele with Arnold Chiari malformation.
Clinical features: Inspiratory stridor at birth
Weak, hoarse cry or aphonia.
If unilateral the patient feel better when placed on the side of
Direct laryngoscopy under local anaesthesia.
Reduction of elevagted intracranial tension.
In bilateral palsy tracheostomy is indicated.
b. Tumors :
d. Webs: are caused due to failure of recanalisation of the
larynx . It can range between a complete occlusion by mucosa and
submucous tissue or partial occlusion by a thin membranous web. It
can occur in supraglottis, glottis and subglottis area. Commonly it
is seen in the glottic area. It occurs in one in 10,000 live
Stridor is inspiratory in nature and is present from birth. The
degree of airway obstruction depends on the extent of the web. The
cry is weak or absent because of fixity of the cord. Symptoms are
not positional in nature.
Tracheostomy may be life saving.
Perforation of the web.
Dilatation of the web.
3. Subglottic causes:
Stenosis - congenital / acquired : is the most common cause of
neonatal airway obstruction. It may either be congenital or
acquired. Subglottic area is the narrowest portion of neonatal
airway. Even a 1mm mucosal oedema in this area is sufficient to
reduced the circumference by 1/3 compromising the airway. Congenital
stenosis is more common in male children. Acquired subglottic
stenosis is due to prolonged intubation, insertion of a large
endotracheal tube etc. These patients present with inspiratory and
expiratory stridor (to & fro stridor).
This condition is diagnosed by performing an endoscopy.
Tracheostomy may be life saving.
Anterior cricoid split
Resection of the stenotic segment with reconstruction
Tumors like hemangioma & cystic hygroma.
Subglottic hemangioma is may be asymptomatic at birth. As it
grows it may produce symptoms at a later date. These children
manifest with stridor, change in voice is possible if the tumor
involves the under surface of the vocal cord. These children become
symptomatic by 6 months. Female child is more commonly affected than
males. Subcutaneous hemangiomas may also be seen in 50% of these
Xray soft tissue lateral view may show an eccentric swelling in
the subglottic region. Endoscopy is diagnostic.
Tracheostomy is indicated to tide over acute crisis
Steroids may be prescribed to reduce subglottic oedema.
4. Tracheal causes:
Tracheomalacia : More or less similar to laryngomalacia. The
stridor produced is expiratory in nature.
Atresia : Often fatal at birth. It is also associated with other
5. Extrinsic causes:
Vascular rings : Compression of trachea and oesophagus due to
abnormalities in the development of great vessels. It could be due
to right sided aortic arch, double aortic arch, anomalous right
subclavian artery, or aberrent left pulmonary artery.
Dyspnoea is present at birth, becomes worse on neck extension.
Stridor is expiratory in nature.
Diagnosis is by:
Contrast CT scans
showing various craniofacial
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