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.