Stidor is a harsh, vibratory sound, caused by turbulent airflow through an obstructed upper airway.
Sx
Stridor is best heard over the upper airways
It usually occurs on inspiration → inward pressure exerted on upper airway to collapse, further diminishing the diameter of airways outside the chest. It doesn't usually occur on expiration, because the column of air pushing up from below opens the upper airway, diminishing obstruction to flow
Stridor however, can occur on inspiration → if obstruction in the upper airways is so severe severe, or it starts involving the chest cavity (e.g. the portion of the trachea down there), even the column of air pushing up in expiration may not be able to assist
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Patient information
Wait ... I understand how with wheeze, you hear it on breathing out. Because when you breath out, you push air out of your body so your chest becomes smaller. But on inspiration, why does this cause collapse? Don't you expand?
You do. But you expand the LOWER airways . The upper airways however, collapse .
I see. And because stridor is generated by airways OUTSIDE the chest, it is on inspiration that you hear it - because this is when this part of the airway collapses?
Exactly !
Pathophysiology
It is caused by obstructions of portions of the airway outside the chest cavity
Airflow velocity within the respiratory tree is higher than normal, causing a vibratory sound
Interpretation
Infectious/inflammation:
Epiglottitis, which was historically caused by Haemophilus influenzae, now uncommon due to the Hib vaccine
URTI (croup), croup is the most common cause of acute stridor in kids 6mo-2yo
Bacterial tracheitis, which can be secondary to a viral infection in the trachea (e.g. croup)
Allergies
Laryngitis
Abscess on the tonsils
Swollen tonsils or adenoids (e.g. with tonsilitis)
Secretions, e.g. phlegm/sputum
Anatomic:
Laryngomalacia, the most common cause of stridor
Foreign body inhalation, most common cause of acute stridor in kids 1-2yo
Vocal cord dysfunction, the next most common cause of infant stridor
Tracheomalacia, the most common cause of expiratory stridor
Tumor (e.g. vocal cord cancer)
Airway injury, including due to Dx tests (bronchoscopy, laryngoscopy), neck surgery, use of a breathing tube
Swelling of the neck/face
Hx
Stridor occurs on inspiration → obstruction in upper airways
Stridor occurs on expiration → severe obstruction in upper airways
"Tripoding", positioning their elbows/hands on their knees, leaning forward, with their neck extended, to give accessory muscles of respiration their most advantageous position, and to open up the upper airways → upper airway obstruction
Barking cough → croup
Worsening at night → croup
Previous URTI → croup, bacterial tracheitis
Coryzal → infection
Fever → infection (including ruling out tracheitis, a medical emergency)
Acute onset → foreign body aspiration, infections e.g. croup, epiglottitis
Long duration → anatomical (laryngomalacia, laryngotracheal stenosis)
Age of onset:
Birth → congenital anatomical (down syndrome)
4-6 weeks → laryngomalacia
1-4yo → croup, epiglottitis, foreign body aspiration
Previous stridor → if no, rules out anatomical (e.g. laryngomalacia)
Difficulty swallowing, causing drooling → upper airway obstruction, especially epiglottitis, foreign body in the esophagus
Hoarseness of void → croup, vocal cord paralysis
Recently playing with a small object prior? → foreign body
Congenital abnormalities, or neck surgeries → anatomic
Haemophilus influenza vaccine → acute epiglottitis is unlikely
Dx
CXR of chest and/or neck → anatomic causes? foreign bodies?
Flexible laryngoscopy → used to view down to the larynx
Bronchoscopy → visualize below the larynx
Tx
ABC's, including oxygenation
See also
Breath sounds
Wheeze (due to narrowing of airways INSIDE the chest cavity, cf. stridor which is narrowing of airways OUTSIDE the chest cavity)
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