What are the causes of airway narrowing in a child?

Causes of Airway Narrowing in Children

Airway narrowing in children results from both anatomic and pathologic causes, with the most common being infectious (viral croup, bacterial tracheitis, epiglottitis), mechanical (foreign body aspiration, tracheomalacia), and inflammatory (asthma, bronchiolitis) etiologies.

Anatomic Vulnerability Factors

Children are uniquely susceptible to airway narrowing due to several developmental characteristics:

• The pediatric airway is significantly narrower in caliber, with the nasal passages contributing up to 50% of total airway resistance in neonates, making even minor congestion potentially life-threatening 1
• Infants below 2-6 months are obligate nasal breathers, so complete or partial nasal obstruction can lead to fatal airway compromise 1
• The immature airway is highly compliant and undergoes progressive stiffening with age, making it more susceptible to collapse and deformation 1
• Peripheral airways in infants are more vulnerable to inflammatory narrowing than in adults, primarily for anatomic reasons 2

Infectious Causes

Upper Airway Infections

Viral croup is the most common cause of acute upper airway obstruction in children, typically affecting those 6 months to 3 years of age 3, 4:

• Presents with characteristic barking cough, inspiratory stridor, and respiratory distress 3, 4
• Caused most commonly by parainfluenza viruses 3
• Results in subglottic narrowing from mucosal inflammation and edema 3

Bacterial tracheitis and epiglottitis are true airway emergencies requiring immediate intervention 4, 5:

• Present with acute onset of severe respiratory distress
• Frequently require endotracheal intubation for airway maintenance 4

Lower Airway Infections

Bronchiolitis causes lower airway obstruction primarily in children aged 2 months to 2 years 6:

• Most commonly caused by respiratory syncytial virus 6
• Results in small airway inflammation and narrowing 6
• Manifests as wheeze, hyperinflation, and respiratory distress 6

Mechanical Causes

Foreign Body Aspiration

Foreign body aspiration is a common cause of airway obstruction in children below 3 years of age 4, 5:

• Can cause complete or partial bronchial obstruction 7
• Partial obstruction creates a one-way valve effect leading to localized hyperinflation 7
• Complete obstruction results in atelectasis distal to the foreign body 7
• Delayed removal beyond 30 days results in bronchiectasis in up to 60% of cases 7

Acquired Structural Abnormalities

Tracheobronchomalacia (central airway collapse) is documented in 34-45% of infants with chronic lung disease 1, 8:

• Results from barotrauma, chronic infection, and effects of prolonged intubation 1
• Presents with monophasic expiratory wheeze unresponsive to bronchodilators 8
• Distinguished from fixed lesions by absence of inspiratory stridor 8
• Causes cyanotic "BPD spells" with increased expiratory effort 1

Subglottic stenosis and granulation tissue develop from prolonged intubation 1:

• Can be evaluated by flexible or rigid bronchoscopy 1
• May require surgical resection or balloon dilation 1

Anatomic Compression

Adenoidal hypertrophy is the most common acquired anatomic cause of nasal obstruction in children 1:

• Results in mouth breathing, nasal speech, and snoring 1
• Main indication for adenoidectomy is sleep apnea from adeno-tonsillar hypertrophy 1

Inflammatory Causes

Asthma causes reversible lower airway obstruction through bronchospasm and inflammation 6:

• Characterized by polyphonic wheeze (distinguishing it from structural causes) 8
• Responds to bronchodilator therapy 8

Gastroesophageal/laryngopharyngeal reflux causes inflammation and narrowing of posterior choanae 1:

• Common in infants with prematurity, neuromuscular disease, or cleft palate 1
• Results in nasal congestion, choking, and recurrent pneumonia 1

Critical Diagnostic Distinctions

Stridor Pattern Recognition

The pattern of stridor indicates the level of obstruction 8, 4:

• Inspiratory stridor suggests laryngeal pathology (laryngomalacia, croup) 8
• Expiratory wheeze indicates intrathoracic tracheal collapse or small airway disease 8
• Biphasic stridor suggests fixed upper airway lesions 8

Wheeze Characteristics

Monophasic wheeze suggests structural airway abnormality, whereas polyphonic wheeze indicates diffuse bronchospasm 8:

• Localized monophonic wheeze may indicate foreign body or tracheomalacia 8
• Wheeze unresponsive to bronchodilators suggests structural rather than inflammatory cause 8

Common Pitfalls to Avoid

• Never assume adequate oxygenation based on awake oxygen saturation alone in infants with chronic lung disease, as hypoxemia during sleep is common and unpredictable 1
• Do not delay bronchoscopy beyond 14 days when foreign body is suspected, as this significantly increases risk of bronchiectasis 7
• Avoid using bronchodilators empirically in children with fixed airway obstruction or tracheomalacia, as they may worsen dynamic collapse by relaxing airway smooth muscle without relieving the underlying obstruction 1
• Do not rely on chest radiographs alone for foreign body diagnosis, as radiolucent objects require CT or bronchoscopy for detection 7, 5
• Never perform blind finger sweeps in suspected foreign body cases, as this may push the object deeper into the airway 3