Stridor (Lung Sound): Overview and Practice Questions (2026)

Stridor is one of the most critical adventitious lung sounds clinicians must be able to recognize, as it often signals significant upper airway obstruction. Unlike lower-airway sounds such as wheezes or crackles, stridor is a loud, high-pitched noise typically heard during inspiration and can often be detected without a stethoscope.

It results from turbulent airflow through a narrowed larynx or trachea and is most commonly encountered in infants and children, though adults may develop stridor from trauma, infection, or post-extubation edema.

In this article, we will explore how stridor develops, the conditions most associated with it, and how respiratory therapists and clinicians should evaluate and respond to this important upper-airway sound.

What Is Stridor?

Stridor is a high-pitched, monophonic sound produced by turbulent airflow through a narrowed upper airway, typically at the level of the larynx or trachea. Unlike other adventitious lung sounds, which often require a stethoscope to detect, stridor is usually audible from the bedside and can be heard during normal breathing. Its presence reflects a significant reduction in airway diameter, causing airflow velocity to increase dramatically as it passes through the obstructed area.

Stridor is most commonly heard during inspiration, when negative pressure pulls the upper airway inward and further narrows the compromised region. However, stridor may also occur during expiration or throughout the entire respiratory cycle depending on the location of the obstruction:

• Inspiratory stridor usually indicates narrowing above the glottis.
• Expiratory stridor suggests narrowing in the lower trachea.
• Biphasic stridor raises concern for fixed, severe upper-airway obstruction.

Because stridor reflects upper-airway compromise rather than lower-airway disease, it requires immediate attention and often urgent intervention. Its quality, timing, and associated symptoms help clinicians determine the severity of obstruction and appropriate treatment strategies.

How Stridor Is Produced

Stridor develops when airflow becomes turbulent as it moves through a narrowed segment of the upper airway. This turbulence generates high-frequency vibrations that create the characteristic loud, high-pitched sound. Understanding this mechanism helps clinicians quickly identify where the obstruction is occurring and how serious it may be.

Turbulent Airflow Through a Narrowed Larynx or Trachea

The upper airway, especially the larynx and trachea, is normally wide enough to allow smooth, laminar airflow. When swelling, inflammation, foreign bodies, or structural abnormalities narrow this space, airflow velocity increases dramatically to compensate. This rapid movement causes vibration of the surrounding tissues, producing the sharp, monophonic sound known as stridor.

Inspiratory vs. Expiratory Stridor

Stridor’s timing provides important clues about the location of the obstruction:

• Inspiratory stridor occurs when a lesion or narrowing sits above the glottis. During inspiration, negative pressure pulls the airway walls inward, worsening the obstruction and intensifying the sound.
• Expiratory stridor suggests narrowing lower in the trachea, where the airway collapses outward during expiration.
• Biphasic stridor indicates a fixed obstruction affecting both phases of breathing and is often more concerning.

Why Stridor Is a Red Flag

Because the upper airway is a rigid, narrow passageway, even small degrees of swelling or obstruction can significantly reduce its diameter—especially in infants and children, whose airways are proportionally smaller. This makes stridor not only a diagnostic clue but a possible emergency sign, requiring rapid assessment to prevent complete airway compromise.

Clinical Conditions Associated With Stridor

Stridor is a hallmark of upper airway obstruction, and identifying its cause is essential for determining appropriate treatment. While stridor can occur in patients of any age, it is particularly common in infants and children due to their smaller airway size.

Croup

Croup is the most common cause of acute stridor in children. It typically presents with a barking cough, hoarseness, and progressive inspiratory and expiratory stridor. Mild cases with no cyanosis or stridor at rest can be managed at home, but stridor accompanied by respiratory distress requires hospitalization and close monitoring.

Laryngomalacia

Laryngomalacia is the leading cause of chronic stridor in infants. In this condition, the soft, immature tissues of the larynx collapse inward during inspiration, creating high-pitched inspiratory stridor. Symptoms may worsen when the infant is feeding, crying, or lying supine.

Epiglottitis

Epiglottitis is a life-threatening bacterial infection that causes inflammation and swelling of the epiglottis. Patients often present with high fever, sore throat, difficulty swallowing, drooling, and stridor. Because the airway can close rapidly, epiglottitis is a true emergency requiring immediate airway management.

Post-Extubation Laryngeal Edema

After removal of an endotracheal tube, some patients develop swelling of the vocal cords or surrounding tissues. Hoarseness is common, but the presence of stridor indicates significant narrowing of the glottic opening. This situation may require racemic epinephrine, steroids, or—if severe—reintubation.

Airway Trauma

Blunt or penetrating trauma to the neck can cause swelling, bleeding, or structural damage that obstructs the airway. Stridor in this context is a warning sign of airway compromise requiring urgent evaluation.

Foreign Body Aspiration

A lodged foreign object in the upper airway can create sudden, severe stridor. This occurs most often in toddlers but can happen in adults as well. Rapid intervention is critical to prevent complete airway obstruction.

Note: Stridor should always be taken seriously, as it often reflects significant and potentially life-threatening airway narrowing.

How to Assess Stridor During Auscultation and Clinical Evaluation

Because stridor often indicates a dangerous degree of upper-airway narrowing, rapid and accurate assessment is essential. Respiratory therapists and clinicians must evaluate not only the sound itself but the patient’s overall respiratory effort and signs of distress.

Listen Without a Stethoscope First

Stridor is often audible from the bedside, even before auscultation. A loud, high-pitched inspiratory sound should immediately raise concern for upper-airway obstruction. If stridor is present at rest, this signals a more advanced condition requiring urgent attention.

Determine the Timing of Stridor

The phase of breathing during which stridor occurs helps identify the level of obstruction:

• Inspiratory stridor indicates narrowing above the glottis.
• Expiratory stridor suggests narrowing in the lower trachea.
• Biphasic stridor points to a fixed obstruction that impairs airflow during both phases.

Note: Timing also helps differentiate stridor from wheezing, which typically occurs during expiration and originates in the lower airways.

Assess the Severity of Respiratory Distress

Stridor is just one part of the clinical picture. Evaluate for:

• Suprasternal or intercostal retractions
• Nasal flaring
• Tachypnea
• Cyanosis
• Drooling (especially in suspected epiglottitis)
• Inability to speak or cry normally
• Agitation or lethargy

Note: These signs indicate increasing airway compromise and help determine whether urgent airway intervention is necessary.

Consider the Patient’s Age and History

Infants and young children develop stridor more readily due to smaller airway diameter. In adults, stridor most often reflects post-extubation edema, trauma, or infection. History-taking should include onset, progression, associated symptoms, recent intubation, infections, trauma, or choking events.

Use Auscultation to Support Findings

While stridor is loudest over the larynx and trachea, auscultation helps confirm location and identify other sounds, such as absent breath sounds or lower-airway wheezing. If breath sounds diminish significantly, this may indicate worsening obstruction and impending airway failure.

Note: Prompt assessment of stridor is essential because delays in intervention can lead to rapid decompensation, especially in pediatric patients.

Why Identifying Stridor Matters in Respiratory Care

Stridor is one of the most important and time-sensitive breath sounds clinicians must recognize. Unlike lower-airway adventitious sounds, stridor often indicates a potentially life-threatening obstruction that requires immediate evaluation and intervention. Early recognition can prevent airway collapse and ensure timely treatment.

Early Detection of Upper Airway Obstruction

Stridor is a clear warning sign that airflow through the upper airway is compromised. Because the larynx and trachea have limited space, even mild swelling or narrowing can significantly reduce airflow—especially in infants and children. Identifying stridor early allows clinicians to act before the obstruction progresses to complete airway blockage.

Differentiating Stridor From Wheezing

Wheezing is typically associated with lower-airway diseases like asthma and congestive heart failure, while stridor reflects obstruction at the level of the larynx or trachea. Confusing the two can lead to inappropriate treatment. Bronchodilators may help wheezing but will not resolve stridor caused by edema, infection, or structural narrowing.

Guiding Urgent Treatment Strategies

The presence and severity of stridor helps determine the need for interventions such as:

• Racemic epinephrine to reduce airway edema
• Systemic or inhaled corticosteroids
• Humidified oxygen therapy
• Airway stabilization or intubation
• Transfer to a higher level of care

Note: Persistent or worsening stridor signals that the airway is unstable and may require immediate advanced airway management.

Preventing Respiratory Failure

Stridor that accompanies retractions, cyanosis, or decreased air movement indicates imminent airway compromise. Early recognition is especially critical for children with croup or patients with post-extubation stridor, as they can deteriorate rapidly without proper intervention.

Supporting Diagnostic Accuracy

Identifying stridor helps clinicians evaluate the underlying condition quickly. For example:

• A barking cough with inspiratory stridor suggests croup.
• Fever, sore throat, and drooling indicate possible epiglottitis.
• Stridor after extubation points to laryngeal edema.
• Sudden-onset stridor raises concern for foreign body aspiration.

Note: Accurate interpretation of stridor ensures appropriate and timely treatment, improving outcomes and preventing complications.

Stridor Practice Questions

1. What does stridor typically indicate when heard over the larynx or trachea?
A significant upper airway obstruction.

2. What is the characteristic sound quality of stridor?
A loud, high-pitched, monophonic sound.

3. During which phase of breathing is stridor most commonly heard?
Inspiration, due to upper airway narrowing.

4. Stridor is most common in which age group?
Infants and young children.

5. What is the most common cause of chronic stridor in infants?
Laryngomalacia

6. What is the most common acute cause of stridor in children?
Croup

7. What does inspiratory stridor usually indicate regarding airway location?
Narrowing above the glottis.

8. What does expiratory stridor suggest?
Obstruction of the lower trachea.

9. What is a common cause of stridor in adults following airway manipulation?
Laryngeal or subglottic edema after intubation.

10. What type of airway problem most often differentiates stridor from wheezing?
Stridor involves upper airway obstruction; wheezing involves intrathoracic obstruction.

11. What are hallmark clinical features of croup?
Inspiratory and expiratory stridor with a barking cough.

12. When should a child with croup be hospitalized?
When stridor occurs at rest with retractions or cyanosis.

13. What symptoms commonly accompany stridor in epiglottitis?
High fever, severe sore throat, and labored breathing.

14. What post-extubation symptom may indicate glottic edema?
Stridor on inspiration.

15. What medication is commonly used via aerosol to treat post-extubation stridor?
Racemic epinephrine (2.25%) or levoepinephrine (1:1000).

16. What is the therapeutic goal when giving racemic epinephrine for stridor?
Reduce airway edema through mucosal vasoconstriction.

17. What additional therapy may help reduce airway inflammation contributing to stridor?
Inhaled or intravenous corticosteroids.

18. What does stridor or markedly decreased air movement after extubation suggest?
Persistent or worsening upper airway obstruction.

19. What should be suspected if stridor does not improve after bronchodilator and steroid therapy?
Structural airway narrowing such as subglottic stenosis.

20. What mechanism generates stridor during airflow?
Rapid airflow through a narrowed upper airway causing vibration of tissues.

21. What type of airway obstruction is suggested when stridor is audible without a stethoscope?
A severe upper airway obstruction.

22. What condition is most associated with a “steeple sign” on a neck radiograph?
Croup causing subglottic narrowing.

23. What radiographic sign is associated with epiglottitis?
The “thumb sign” indicating an enlarged epiglottis.

24. Why is agitation dangerous in a child with stridor?
It increases oxygen demand and worsens airway obstruction.

25. What is the safest action when epiglottitis is suspected?
Avoid throat inspection and secure the airway emergently if needed.

26. What patient position may temporarily improve stridor from upper airway swelling?
Sitting upright to reduce airway collapse and improve airflow.

27. What type of airflow pattern contributes to the high-pitched sound of stridor?
Turbulent airflow through a narrowed upper airway.

28. What finding suggests impending upper airway obstruction in a child with stridor?
Increasing retractions and declining air movement.

29. Which condition is characterized by chronic inspiratory stridor that improves when prone?
Laryngomalacia due to supraglottic tissue collapse.

30. What is the most likely cause of biphasic stridor?
A fixed obstruction such as subglottic stenosis.

31. Why is humidified oxygen beneficial for patients with stridor?
It helps reduce airway dryness and irritation, easing airflow.

32. What does sudden onset of stridor in a previously healthy child strongly suggest?
Foreign body aspiration.

33. What assessment should be performed immediately if stridor worsens after extubation?
Evaluate for post-extubation laryngeal edema.

34. What condition can cause stridor due to fluid accumulation in the airway tissues?
Angioedema.

35. What type of cough is commonly associated with stridor from croup?
A barking, seal-like cough.

36. What clinical indicator helps differentiate stridor from upper airway snoring sounds?
Stridor persists when awake and upright, unlike snoring.

37. What should be monitored closely after giving racemic epinephrine for stridor?
Rebound airway swelling and return of symptoms.

38. What does decreased intensity of stridor paired with decreased air movement indicate?
Worsening obstruction and possible respiratory failure.

39. What common home exposure can trigger acute upper airway swelling leading to stridor?
Inhalation of hot steam or smoke.

40. What breath sound may accompany stridor during severe airway swelling?
Diminished or absent breath sounds below the obstruction.

41. What condition causes stridor by narrowing the airway due to thick, inflamed tissues in infants?
Bronchiolitis-associated upper airway swelling.

42. What intervention may prevent stridor in patients with a history of post-extubation airway edema?
Administering steroids 12–24 hours before extubation.

43. What symptom combination strongly suggests epiglottitis in a child with stridor?
Drooling, tripod position, and muffled voice.

44. When stridor appears during exertion but not at rest, what should be suspected?
Mild upper airway narrowing or exercise-induced laryngeal obstruction.

45. What surgical complication may cause stridor due to nerve involvement?
Vocal cord paralysis after thyroid or neck surgery.

46. What mechanism explains inspiratory stridor in upper airway obstruction?
Airway collapse during negative intrathoracic pressure on inhalation.

47. What mechanism explains expiratory stridor in lower tracheal obstruction?
Dynamic airway collapse during forced airflow out of the lungs.

48. What bedside tool can help differentiate upper airway obstruction from lower airway obstruction?
Flow-volume loop showing variable extrathoracic or intrathoracic obstruction.

49. What patient complaint often precedes stridor in progressive upper airway swelling?
Hoarseness due to vocal cord involvement.

50. What finding indicates the need for immediate airway intervention in a patient with stridor?
Inability to speak full sentences or severe retractions with cyanosis.

51. What does the presence of stridor at rest indicate about the severity of airway obstruction?
It indicates a moderate-to-severe obstruction requiring immediate evaluation.

52. What physiologic change causes stridor to worsen when a patient becomes anxious?
Increased respiratory effort leads to greater turbulent airflow through a narrowed airway.

53. What upper airway structure commonly swells after prolonged intubation, causing stridor?
The vocal cords and surrounding glottic tissues.

54. What is the significance of drooling in a patient presenting with stridor?
It suggests inability to swallow due to severe upper airway obstruction.

55. Why is racemic epinephrine effective in treating stridor from croup?
It causes mucosal vasoconstriction that reduces subglottic edema.

56. What condition should be suspected when stridor improves with neck extension?
Dynamic upper airway narrowing relieved by positional change.

57. What finding differentiates stridor caused by foreign body aspiration from infections like croup?
Sudden onset with no preceding illness.

58. What effect does cool mist have on children presenting with mild viral-induced stridor?
It may soothe irritated tissues and reduce upper airway swelling.

59. Why is stridor often more pronounced during inspiration than expiration?
Negative pressure during inhalation collapses narrowed supraglottic structures.

60. What underlying issue should be considered when stridor is accompanied by a weak cry in an infant?
Severe airway narrowing affecting vocal cord function.

61. What does the presence of suprasternal retractions with stridor indicate?
Significant upper airway resistance requiring urgent management.

62. Which disorder can produce intermittent stridor triggered by exercise or stress?
Vocal cord dysfunction.

63. Why should deep oral suctioning be avoided in suspected epiglottitis?
It can provoke airway spasm and sudden obstruction.

64. What bedside observation helps determine if stridor is getting worse?
Increasing use of accessory muscles or decreasing air movement.

65. What condition may cause stridor due to abnormal cartilage development in infants?
Tracheomalacia

66. What key assessment differentiates stridor from wheezing?
Stridor is loudest over the neck rather than the lung fields.

67. Why is heliox sometimes used in patients with severe stridor?
Its lower density reduces airflow resistance through narrowed upper airways.

68. What laryngeal condition can present with inspiratory stridor following trauma?
Vocal cord edema or hematoma.

69. What finding suggests partial rather than complete upper airway obstruction?
Presence of stridor instead of silent airway movement.

70. Which condition produces high-pitched, harsh stridor during both inspiration and expiration?
Fixed upper airway obstruction.

71. Why is fever especially concerning in a child with stridor?
It increases suspicion for epiglottitis or bacterial tracheitis.

72. What type of airway obstruction is suggested when stridor improves after coughing?
Secretions partially blocking the upper airway.

73. What symptom suggests that stridor is progressing toward respiratory failure?
Decreased intensity of stridor with diminished breath sounds.

74. What congenital abnormality may cause stridor that worsens with feeding?
Vascular ring compressing the trachea.

75. Why is a calm environment important when evaluating pediatric stridor?
Crying can drastically worsen airway obstruction.

76. What type of stridor is commonly heard in post-extubation laryngeal edema?
Inspiratory stridor due to glottic narrowing.

77. What clinical clue suggests bacterial tracheitis rather than croup?
Toxic appearance with high fever and poor response to racemic epinephrine.

78. What factor explains why stridor is more common in infants than adults?
Infants have smaller, more compliant airways prone to collapse.

79. What intervention may be necessary if stridor persists despite medical therapy?
Advanced airway placement.

80. What is a key indicator distinguishing structural airway obstruction from inflammatory swelling?
A constant, unchanging level of stridor regardless of illness progression.

81. What does the absence of stridor despite severe upper airway obstruction indicate?
A critically narrowed airway with minimal airflow, signaling impending respiratory failure.

82. What condition should be suspected when stridor worsens during feeding in an infant?
Laryngomalacia or other dynamic supraglottic collapse.

83. What diagnostic test can reveal flattening of inspiratory flow, suggesting extrathoracic obstruction with stridor?
Flow-volume loop

84. What clue suggests that stridor is caused by subglottic stenosis rather than inflammation?
A chronic, persistent pattern not responsive to racemic epinephrine.

85. What is the likely cause when stridor presents with a barking cough and low-grade fever?
Viral croup

86. What is a red-flag sign when stridor is accompanied by an inability to lie flat?
Severe upper airway compromise requiring immediate intervention.

87. Why is hydration important for children with mild stridor from infections?
Thick secretions can exacerbate airway narrowing and worsen symptoms.

88. What type of stridor is produced when upper airway narrowing occurs at the glottic level?
High-pitched, harsh inspiratory stridor.

89. What airway condition produces biphasic stridor and is often related to scarring?
Fixed subglottic stenosis.

90. What does stridor that becomes quieter while respiratory distress increases suggest?
Airflow collapse and failing respiratory effort.

91. What condition should be suspected when stridor is positional, improving when the patient is prone?
Dynamic airway obstruction such as laryngomalacia.

92. What symptom accompanying stridor may indicate an allergic reaction?
Rapid onset of facial or throat swelling.

93. Why is rapid intervention needed when stridor is accompanied by drooling and difficulty swallowing?
These signs point to severe supraglottic obstruction.

94. What laryngeal issue commonly causes post-extubation stridor in adults?
Vocal cord edema resulting from ETT irritation.

95. Which airway assessment finding suggests stridor is caused by inhalation of a foreign object?
Unilateral decreased breath sounds with sudden onset stridor.

96. What medication class may help reduce airway inflammation associated with persistent stridor?
Systemic or inhaled corticosteroids.

97. Why is the “sniffing position” sometimes helpful in patients with mild inspiratory stridor?
It aligns airway structures and improves airflow.

98. What is the most likely diagnosis when stridor improves significantly after racemic epinephrine?
Subglottic swelling consistent with croup.

99. What upper airway disorder may cause stridor that is worse during exertion but absent at rest?
Vocal cord dysfunction.

100. What intervention should be considered when stridor persists despite bronchodilators, steroids, and racemic epinephrine?
Evaluation for mechanical obstruction requiring ENT or airway specialty intervention.

Final Thoughts

Stridor is a critical clinical finding that signals obstruction in the upper airway and often requires rapid assessment and intervention. Unlike wheezing or crackles, which originate in the lower airways, stridor arises from turbulent airflow through a narrowed larynx or trachea and is frequently audible without a stethoscope.

Understanding its characteristic high-pitched quality, the conditions that cause it, and the difference between inspiratory, expiratory, and biphasic stridor helps clinicians accurately identify the source of obstruction. Because stridor can accompany life-threatening conditions such as epiglottitis, severe croup, post-extubation edema, or airway trauma, early recognition is essential for preventing respiratory failure and protecting the airway.

For respiratory therapists and healthcare providers, the ability to promptly assess and respond to stridor is a vital component of effective airway management and emergency care.