Airway obstruction and congenital airway disease

Definition / Overview

Upper airway obstruction (UAO) in children encompasses any process that impairs airflow from the nares through to the subglottis. Because paediatric airways are narrower, shorter, and more compliant than adult airways, resistance increases exponentially with even modest reductions in calibre (resistance $\propto \frac{1}{r^4}$ by Poiseuille's law). The PICU clinician must simultaneously:

• Localise the level of obstruction (supraglottic, glottic, subglottic, tracheal, bronchial)
• Distinguish dynamic from fixed obstruction
• Differentiate congenital structural causes from acute acquired causes
• Recognise impending complete obstruction before it occurs

Pathophysiology and Developmental Anatomy

Why children are vulnerable

• The infant larynx sits at C3-C4 (versus C4-C6 in adults), with a more anterior and cephalad position; this narrows with growth.
• The subglottis is the narrowest fixed point in the paediatric airway until approximately 8-10 years; even 1 mm of circumferential subglottic oedema reduces cross-sectional area by roughly 75%.
• Cartilaginous support of the trachea and bronchi matures progressively; premature infants and neonates have the most compliant (and therefore most collapsible) airways.
• Airway muscle tone is the primary defence against dynamic collapse; any process reducing tone (sedation, anaesthesia, sleep, neurological disease) exacerbates obstruction.

Pressure dynamics and localisation

During inspiration, extrathoracic airway pressure falls below atmospheric pressure, tending to collapse the supraglottic and tracheal lumen. During expiration, intrathoracic pressure rises, tending to collapse intrathoracic airways.

Clinical Assessment

History

• Age of onset: stridor from the first days of life strongly suggests a congenital structural cause.
• Speed of onset: acute onset with fever points to croup, epiglottitis, or bacterial tracheitis; gradual onset with worsening over weeks suggests progressive structural lesion (haemangioma, cyst, extrinsic compression).
• Position: laryngomalacia often worse supine and when crying; tracheomalacia often worse prone or in extension.
• Cry / voice quality: weak or husky cry suggests vocal cord involvement; normal cry with inspiratory noise suggests supraglottic disease.
• Feeding difficulty / aspiration: seen with vocal cord palsy, laryngeal cleft, and severe laryngomalacia.
• Prior intubation: acquired subglottic stenosis and subglottic cysts.
• Prematurity / congenital syndromes: Down syndrome (tracheal hypoplasia, subglottic stenosis), Pierre Robin (retrognathia, glossoptosis), CHARGE, 22q11 deletion.

Examination

• Work of breathing: subcostal, intercostal, suprasternal recession; tracheal tug.
• Presence and timing of stridor.
• Oxygen saturation: note that $SpO_2$ may be maintained until very late; do not use $SpO_2$ alone as a reassurance tool.
• Voice/cry quality; swallowing; drooling.
• Signs of right heart strain in chronic severe UAO (cor pulmonale, oedema).
• Skin: cutaneous haemangiomas in 50% of children with subglottic haemangioma (particularly "beard" distribution).

Specific Conditions: Diagnosis and PICU Management

Laryngomalacia

The most common cause of neonatal/infant stridor. Results from supraglottic floppiness: the omega-shaped epiglottis, short aryepiglottic folds, and redundant mucosa over the arytenoids prolapse into the airway on inspiration.

• Presentation: intermittent inspiratory stridor from birth or first weeks; worse with feeds, crying, supine position; normal cry.
• Course: typically self-limiting; resolves by 12-18 months in most cases.
• Diagnosis: awake flexible nasolaryngoscopy is the primary tool; dynamic supraglottic collapse on inspiration is diagnostic.
• PICU indications: severe cases with failure to thrive, hypoxia, cyanotic episodes, cor pulmonale, or apnoea.
• Management:
  1. Positioning: prone or lateral in infants; elevation of head of bed.
  2. Anti-reflux therapy (commonly co-prescribed; evidence modest).
  3. High-flow nasal cannula (HFNC) as a bridge for moderate-severe cases awaiting surgical intervention.
  4. Supraglottoplasty (aryepiglottoplasty): ENT procedure of choice for severe disease; reserve for failure to thrive, recurrent hypoxia, feeding failure.
  5. Tracheostomy: rarely required; reserved for failed supraglottoplasty or neurological laryngomalacia.

Tracheomalacia and Bronchomalacia

Excessive dynamic collapse of the trachea ($>50\%$ luminal reduction on expiration) or bronchi during breathing. May be primary (intrinsic cartilaginous weakness) or secondary (extrinsic compression by vascular anomaly, oesophageal atresia repair, mediastinal mass).

• Presentation: expiratory or biphasic stridor; "barking" or "brassy" cough; recurrent lower respiratory infections; apnoea in infants. Secondary bronchomalacia presents with air trapping or lobar collapse.
• Diagnosis: dynamic CT bronchogram or flexible bronchoscopy under spontaneous breathing (collapse is lost under positive pressure).
• PICU management:
  • CPAP/HFNC provides pneumatic stenting of the airway; minimum CPAP of 5-8 cmH₂O often effective.
  • In intubated patients, avoid excessive sedation-induced respiratory depression; maintain some respiratory effort where possible.
  • Post-extubation CPAP bridge is often required.
  • Aortopexy or tracheopexy for severe tracheomalacia associated with oesophageal atresia repair.
  • Tracheostomy with ventilatory support rarely needed for most severe primary tracheomalacia.

Vocal Cord Palsy

Unilateral palsy:

• Usually presents with a weak, husky, or breathy cry; feeding difficulties and aspiration risk.
• Stridor is typically absent unless concurrent airway swelling exists.
• Causes: birth trauma (left cord more commonly; recurrent laryngeal nerve stretch), post-cardiac or thoracic surgery (patent ductus arteriosus ligation, tracheo-oesophageal fistula repair, aortic arch surgery), iatrogenic.
• Management: primarily supportive; thickened feeds for aspiration; most congenital cases recover spontaneously over months.

Bilateral palsy:

• Presents with inspiratory or biphasic stridor; cords lie in or near the paramedian position, severely restricting the airway.
• Associated with central neurological anomalies in a significant proportion: Arnold-Chiari malformation, hydrocephalus, brainstem dysgenesis; always perform neuroimaging.
• Diagnosis: dynamic microlaryngoscopy.
• Management:
  1. PICU admission; supplemental oxygen and HFNC for mild-moderate.
  2. Most will require tracheostomy; decannulation possible as neurological recovery or airway growth occurs (often 1-4 years).
  3. Posterior cordotomy or lateralisation procedures as ENT options for selected older patients.

Acute Inflammatory UAO

Croup (Laryngotracheobronchitis)

• Most common acute infectious UAO; typically 6 months to 3 years; parainfluenza virus predominant.
• Westley croup score guides severity; moderate-severe requires PICU-level monitoring.
• Management:
  1. Minimise distress; allow position of comfort.
  2. Dexamethasone 0.15-0.6 mg/kg orally or IV (single dose; oral and IV are equivalent); consider even mild croup.
  3. Nebulised adrenaline (racemic adrenaline 2.25% or L-adrenaline 1:1000 at 0.5 mL/kg to maximum 5 mL) for moderate-severe; monitor for rebound over 2-4 hours.
  4. Heliox (Helium:Oxygen 70:30 or 80:20) as temporising measure for severe obstruction; reduces turbulent flow resistance.
  5. Intubation: use an uncuffed or cuffed ETT 0.5-1 size smaller than predicted (age/4 + 3.5 for cuffed, age/4 + 4 for uncuffed); expect subglottic resistance on insertion.
  6. Extubation when air leak audible at $<30\,\text{cmH}_2\text{O}$ and child clinically improving.

Epiglottitis

• Rare post-Hib vaccination era; still occurs (non-typeable Haemophilus, group A Streptococcus, Staphylococcus aureus).
• Do not examine the throat, attempt IV access, or lay the child supine before a definitive airway is secured in theatre.
• Classic triad: toxic appearance, drooling, dysphagia; child prefers tripod / sniffing position; rapid progression to complete obstruction.
• Management: emergency transfer to theatre with ENT surgeon and anaesthetist present; inhalational induction; oral intubation with smaller tube; IV access once airway secured; IV cefotaxime 50 mg/kg 6-hourly or ceftriaxone 50 mg/kg daily.
• PICU intubation typically 24-48 hours; extubation when afebrile, leak present, oedema resolved on flexible laryngoscopy.

Bacterial Tracheitis

• Subacute presentation; Staphylococcus aureus (including MRSA) most common; pseudomembranous exudate causes partial or complete tracheal obstruction.
• Distinguished from croup by high fever, toxaemia, failure to respond to adrenaline/dexamethasone.
• Requires early intubation (often difficult; membrane may be dislodged into ETT); frequent ETT suctioning every 1-2 hours to maintain patency; anti-staphylococcal antibiotics (flucloxacillin 50 mg/kg 6-hourly IV; add vancomycin 15 mg/kg 6-hourly if MRSA concern).

Congenital Structural Anomalies

Subglottic Stenosis

• Congenital: incomplete canalisation of the cricoid region; presents with recurrent "croup"-like episodes or biphasic stridor.
• Acquired: most common cause is prolonged endotracheal intubation; risk factors include infection, excessive movement, oversized tube.
• Grading (Cotton-Myer): I ($<50\%$ obstruction) to IV (complete obstruction).
• Management: mild-moderate: observe and optimise; tracheostomy if recurrent critical obstruction; definitive: laryngotracheal reconstruction (LTR) with costal cartilage grafting or cricotracheal resection for severe grades.

Subglottic Haemangioma

• Presents with biphasic or inspiratory stridor at 6-12 weeks of age; may worsen over first year then involute.
• 50% have cutaneous haemangiomas (especially "beard" distribution).
• Management: propranolol 1-3 mg/kg/day oral (in divided doses); dramatic response expected; monitor for hypoglycaemia, bradycardia, bronchospasm. Reserve tracheostomy and laser therapy for propranolol failure.

Laryngeal Webs and Atresia

• Anterior glottic webs most common; present with weak cry or aphonia; biphasic stridor if significant.
• Thin anterior webs: endoscopic division or dilation; thick webs require LTR.
• Laryngeal atresia: rare; presents at delivery with absence of cry and failure to ventilate; requires immediate surgical airway.

Laryngeal Cleft

• Posterior midline deficiency between larynx and oesophagus; ranges from Type I (supraglottic, above vocal cords) to Type IV (extends into thoracic oesophagus).
• Presents with aspiration, recurrent pneumonia, feeding difficulty; diagnosis confirmed at microlaryngoscopy.
• PICU: strict aspiration precautions; nasogastric or nasojejunal feeding; surgical repair by laryngeal cleft repair for Types II-IV.

Vascular Rings and Slings

• Double aortic arch and right aortic arch with aberrant left subclavian artery are most common vascular rings causing tracheal compression.
• Pulmonary artery sling (left PA arising from right PA, passing between trachea and oesophagus): commonly associated with complete tracheal rings and tracheal stenosis.
• Presentation: expiratory stridor, recurrent respiratory infections, dysphagia; symptoms often worse prone.
• Diagnosis: CT angiography (modality of choice in PICU); bronchoscopy demonstrates extrinsic pulsatile compression.
• Management: surgical division/repair; underlying tracheomalacia may persist post-repair and require CPAP support.

Congenital Pulmonary Anomalies at the PICU Interface

Investigations

Complications and Special Considerations

Airway Management Principles in UAO

• Never sedate a child with UAO without immediate airway rescue capability.
• Use inhalational induction (sevoflurane) for suspected epiglottitis, severe croup, or fixed subglottic stenosis.
• Have ENT/surgical team available for potential surgical airway in severe cases.
• ETT sizing for children: cuffed ETT internal diameter $= \text{age}/4 + 3.5\,\text{mm}$; uncuffed $= \text{age}/4 + 4\,\text{mm}$; use $0.5$ size smaller when subglottic narrowing anticipated.
• Cuff pressure: maintain $\leq 20\,\text{cmH}_2\text{O}$ to minimise mucosal ischaemia.

Post-Extubation UAO

• Dexamethasone 0.25-0.5 mg/kg IV 6-12 hours before and after extubation reduces post-extubation stridor in high-risk patients.
• Nebulised adrenaline 0.5 mL/kg of 1:1000 (max 5 mL) for post-extubation stridor.
• HFNC or CPAP bridge post-extubation for tracheomalacia or known subglottic disease.

Tracheostomy in the PICU

• Indications: prolonged ventilatory dependence, failed extubation from anatomical UAO, bilateral vocal cord palsy, severe subglottic/tracheal stenosis, complex craniofacial syndrome requiring long-term airway support.
• Children with tracheostomy in the PICU require written emergency protocols at the bedside (tube size, inner diameter, length, emergency replacement procedure) and first-pass tube change should not occur before post-operative day 5-7.
• Humidification is mandatory; paediatric speaking valves (Passy-Muir) can be trialled once cuffless or deflated cuff in appropriate patients.

Chronic UAO Consequences

• Obstructive sleep apnoea: nocturnal hypoventilation, cor pulmonale, polycythaemia, growth failure.
• Recurrent aspiration pneumonia in laryngeal/vocal cord pathology.
• Feeding failure and failure to thrive in severe laryngomalacia and vocal cord palsy.

Key Viva and Hot-Case Framing

• "Stridor in a neonate from day 1": congenital structural cause until proven otherwise; arrange flexible nasolaryngoscopy and, if inconclusive, microlaryngoscopy/bronchoscopy under GA with ENT.
• "Child with expiratory wheeze not responding to bronchodilators": consider tracheomalacia, vascular ring, or intrathoracic airway anomaly; request dynamic CT and refer for bronchoscopy.
• "Post-cardiac-surgery hoarse cry and feeding difficulty": recurrent laryngeal nerve injury; arrange nasolaryngoscopy to confirm; thicken feeds; most recover within 6-12 months.
• "Infant with beard-distribution haemangioma and biphasic stridor": subglottic haemangioma until proven otherwise; start propranolol after echo to exclude cardiac contraindications; arrange urgent microlaryngoscopy.
• "Croup not responding to adrenaline and steroids": consider bacterial tracheitis, epiglottitis in unvaccinated child, or foreign body; prepare for intubation in a controlled setting.