Stridor
Why is this topic important?
Stridor is one of the most important respiratory signs in paediatrics and a favourite MRCPCH examination topic.
Unlike wheeze, which originates from the lower airways, stridor indicates upper airway obstruction and may be a sign of a potentially life-threatening condition.
Candidates are expected to:
Recognise stridor
Understand the anatomical site of obstruction
Differentiate common causes
Identify red flag features
Understand emergency management principles
Stridor commonly appears in MRCPCH clinical scenarios involving croup, epiglottitis, laryngomalacia and foreign body aspiration.
Definition
Stridor is a harsh, high-pitched respiratory sound caused by turbulent airflow through a partially obstructed upper airway.
It is a sign, not a diagnosis.
The location and timing of stridor help identify the level of airway obstruction.
Key MRCPCH Facts
Stridor indicates upper airway obstruction.
Inspiratory stridor usually indicates obstruction above the thoracic inlet.
Biphasic stridor often indicates more severe obstruction at the level of the larynx or subglottis.
Expiratory stridor suggests tracheal obstruction.
Stridor is different from wheeze.
A child with stridor should always be assessed for severity and airway compromise.
Drooling, toxic appearance and tripod positioning are red flags.
Anatomy and Pathophysiology
Upper Airway Structures
Stridor may arise from obstruction at the:
Nasopharynx
Oropharynx
Larynx
Subglottic region
Trachea
Why Children Are More Vulnerable
Children have:
Smaller airways
More compliant airway structures
Greater effect of airway swelling
A small amount of oedema can significantly reduce airflow.
Types of Stridor
Inspiratory Stridor
Suggests obstruction at:
Supraglottic region
Glottis
Subglottic airway
Examples:
Croup
Laryngomalacia
Epiglottitis
Biphasic Stridor
Suggests fixed airway obstruction.
Examples:
Severe croup
Subglottic stenosis
Airway haemangioma
Expiratory Stridor
Suggests intrathoracic tracheal obstruction.
Examples:
Tracheomalacia
Tracheal compression
Causes of Stridor
Acute Causes
Croup
Most common cause.
Features:
Barking cough
Hoarse voice
Inspiratory stridor
Epiglottitis
Medical emergency.
Features:
High fever
Drooling
Toxic appearance
Difficulty swallowing
Foreign Body Aspiration
Features:
Sudden onset
Choking episode
Unilateral chest signs may coexist
Anaphylaxis
Features:
Rapid onset
Facial swelling
Urticaria
Airway oedema
Chronic Causes
Laryngomalacia
Most common cause of chronic stridor in infancy.
Features:
Inspiratory stridor from birth
Worse when feeding
Worse when lying flat
Improves with age
Vocal Cord Palsy
May present with:
Stridor
Weak cry
Feeding difficulties
Subglottic Stenosis
May be congenital or acquired.
Often associated with previous intubation.
Airway Haemangioma
May present with progressive stridor during infancy.
Clinical Assessment
History
Important questions:
Acute or chronic?
Sudden or gradual onset?
Associated fever?
Choking episode?
Feeding difficulties?
Previous intubation?
Examination
Assess:
Work of breathing
Respiratory rate
Oxygen saturation
Level of consciousness
Feeding ability
Red Flag Features
Urgent senior review is required if:
Stridor at rest
Drooling
Toxic appearance
Cyanosis
Severe recession
Reduced consciousness
Exhaustion
Silent airway
These features suggest significant airway compromise.
Differential Diagnosis
Stridor vs Wheeze
Stridor
Upper airway obstruction
Usually inspiratory
Loudest over neck
Wheeze
Lower airway obstruction
Usually expiratory
Loudest over chest
This distinction is commonly tested in MRCPCH examinations.
Investigations
Mild Cases
May require no investigation.
Flexible Nasendoscopy
Useful for:
Laryngomalacia
Vocal cord dysfunction
Imaging
May include:
Neck X-ray
Chest X-ray
CT scan (selected cases)
Bronchoscopy
Gold standard investigation for many structural airway abnormalities.
Management
Management depends on the underlying cause.
General Principles
Keep child calm
Avoid unnecessary distress
Continuous monitoring if severe
Croup
Dexamethasone
Nebulised adrenaline if severe
Epiglottitis
Airway emergency
Senior anaesthetic and ENT involvement
Intravenous antibiotics
Foreign Body Aspiration
Urgent airway assessment
Bronchoscopy
Anaphylaxis
Intramuscular adrenaline
Airway management
Laryngomalacia
Most cases:
Observation
Reassurance
Severe cases:
ENT referral
Supraglottoplasty
Complications
Acute
Respiratory failure
Complete airway obstruction
Cardiorespiratory arrest
Chronic
Feeding difficulties
Poor weight gain
Recurrent hospital admissions
Common Exam Traps
Trap 1
Stridor is a sign, not a diagnosis.
Trap 2
Stridor indicates upper airway obstruction.
Trap 3
Wheeze indicates lower airway obstruction.
Trap 4
Drooling suggests epiglottitis rather than croup.
Trap 5
Laryngomalacia is the commonest cause of chronic stridor in infancy.
Trap 6
A quieter stridor in a deteriorating child may indicate worsening airway obstruction rather than improvement.
Trap 7
Do not force examination of the throat in suspected epiglottitis.
One Minute Revision
Stridor = upper airway obstruction.
Inspiratory = supraglottic or laryngeal obstruction.
Biphasic = fixed airway obstruction.
Croup = commonest acute cause.
Laryngomalacia = commonest chronic cause.
Drooling + toxic child = epiglottitis.
Stridor ≠ wheeze.
Related Question of the Day
A 10-month-old infant has inspiratory stridor since birth. Symptoms worsen when feeding and improve when prone. What is the most likely diagnosis?
A. Croup
B. Epiglottitis
C. Laryngomalacia
D. Asthma
E. Bronchiolitis
Answer
C. Laryngomalacia
Explanation
Laryngomalacia is the commonest cause of chronic stridor in infancy and typically presents with inspiratory stridor that worsens during feeding, crying or when lying supine.
Related Topics
Croup
Epiglottitis
Foreign Body Aspiration
Asthma
Bronchiolitis
Suggested References
NICE Clinical Knowledge Summary
RCPCH Guidance
BNF for Children
Nelson Textbook of Pediatrics
Illustrated Textbook of Paediatrics
Kendig's Disorders of the Respiratory Tract in Children
Advanced Paediatric Life Support (APLS)
Disclaimer
These notes are intended for MRCPCH revision and educational purposes only. They do not replace local, national or institutional guidelines. Clinical decisions should always be based on current guidance, senior advice and individual patient circumstances.
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