11.1 Acute Upper Airway Obstruction (Croup, Epiglottitis, Bacterial Tracheitis, Foreign Body)

Acute Upper Airway Obstruction: Croup, Epiglottitis, Bacterial Tracheitis, and Foreign Body Airway Obstruction

Acute upper airway obstruction in pediatric patients constitutes an immediate threat to life. Anatomical differences make infants and young children extraordinarily susceptible to rapid decompensation. Successful interfacility transport hinges upon understanding the underlying pathophysiology, recognizing pathognomonic physical signs, avoiding clinical maneuvers that provoke airway collapse, and executing definitive rescue interventions.

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Anatomical Vulnerabilities & Poiseuille's Law of Airway Resistance

The pediatric airway is not merely a miniaturized adult airway; it possesses distinct anatomical and geometric characteristics that heighten vulnerability to obstruction:

1. Funnel-Shaped Airway: In infants and young children, the airway is funnel-shaped (conical), with the narrowest non-distensible point located at the nondistensible cricoid cartilage ring (subglottic space), unlike the adult airway where the narrowest point is the glottic opening (vocal cords).
2. Large Cranium & Occiput: A prominent occiput forces the neck into passive flexion when the child lies supine on a flat stretcher, spontaneously occluding the pharyngeal airway unless a small shoulder roll is placed beneath the upper torso.
3. Macroglossia & Cephalad Larynx: Relative to oral cavity volume, the pediatric tongue is disproportionately large. The larynx sits higher and more anteriorly in the neck (at the level of C3–C4 in infants versus C4–C5 in adults), and the epiglottis is long, narrow, floppy, and U- or omega-shaped, projecting obliquely over the laryngeal inlet.

Mathematical Mechanics of Poiseuille's Law

Resistance ($R$) to laminar airflow through a cylindrical conduit is governed by Poiseuille's Law, which states that resistance is inversely proportional to the fourth power of the internal airway radius ($r$):

$$R \propto \frac{8\eta l}{\pi r^4}$$

• In a healthy neonate or infant with a baseline subglottic diameter of 4 mm ($r = 2\text{ mm}$), just 1 mm of circumferential mucosal edema reduces the luminal diameter to 2 mm ($r = 1\text{ mm}$).
• Resistance Impact: Calculating the fold-increase in resistance: $(r_1 / r_2)^4 = (2 / 1)^4 = 16 / 1 = 16\text{-fold increase}$ (a 1,600% increase in airflow resistance).
• Cross-Sectional Area Impact: Luminal area ($A = \pi r^2$) drops from $\pi(2)^2 = 4\pi$ to $\pi(1)^2 = 1\pi$, representing an acute 75% reduction in cross-sectional area.
• By contrast, in an adult with an 8 mm airway ($r = 4\text{ mm}$), 1 mm of circumferential edema narrows the diameter to 6 mm ($r = 3\text{ mm}$), increasing resistance by only $(4 / 3)^4 \approx 3.16\text{-fold}$ (316%). This physical law explains why minor inflammatory swelling precipitates catastrophic stridor and respiratory failure in toddlers.

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Viral Laryngotracheobronchitis (Croup)

Viral croup is the most prevalent cause of acute infectious upper airway obstruction in children aged 6 months to 3 years (peaking in the second year of life).

• Etiology: Parainfluenza viruses (primarily types 1 and 2) account for over 75% of cases. Other culprits include respiratory syncytial virus (RSV), adenovirus, and influenza A/B.
• Pathophysiology: Viral invasion incites mucosal inflammation, hyperemia, and localized edema strictly within the subglottic trachea. Because the rigid cricoid ring cannot expand outward, swelling expands inward, compressing the subglottic lumen.
• Clinical Features: Follows a 1-to-3-day viral prodrome of low-grade fever, rhinorrhea, and pharyngitis. The child abruptly develops a harsh, metallic "barking seal" cough, hoarse phonation, and inspiratory stridor that typically intensifies at night and with agitation.
• Radiography: Anteroposterior (AP) soft-tissue neck radiograph displays symmetrical tapering of the subglottic airway column, famously designated the "steeple sign" (or "pencil-point sign"). However, diagnosis is primarily clinical, and radiography must never delay emergency therapy.

The Westley Croup Score

The Westley score standardizes clinical severity:

• Inspiratory Stridor: None (0), with agitation (1), at rest (2)
• Retractions: None (0), mild (1), moderate (2), severe (3)
• Air Entry: Normal (0), decreased (1), severely decreased (2)
• Cyanosis: None (0), with agitation (4), at rest (5)
• Level of Consciousness: Normal (0), disoriented/lethargic (5)
• Severity Categories: Mild (≤ 2), Moderate (3–5), Severe (6–11), Impending Respiratory Failure (≥ 12).

Pharmacotherapy & The Racemic Epinephrine Rebound Window

1. Dexamethasone: Administer 0.6 mg/kg orally, IV, or IM (maximum 16 mg). Dexamethasone reduces subglottic capillary permeability and cellular inflammation. It has an onset of action of 1 to 2 hours and an extended biological half-life of 36 to 72 hours. A single dose is effective for mild, moderate, and severe croup.
2. Nebulized Racemic Epinephrine: Administer 0.5 mL of a 2.25% solution diluted in 3 mL of normal saline (or 5 mL of standard 1:1,000 [1 mg/mL] L-epinephrine) delivered via nebulizer or blow-by mask.
   • Mechanism: Alpha-1 adrenergic stimulation induces profound precapillary arteriolar vasoconstriction in the subglottic mucosa, rapidly shrinking interstitial edema and expanding the airway diameter within 10 to 30 minutes.
   • Return of Symptoms ('Rebound'): The effect of racemic epinephrine wears off within about 2 hours, and stridor and retractions can return as it does. Studies suggest symptoms usually return toward the pre-treatment baseline rather than becoming worse, but a child whose underlying edema is progressing can deteriorate.
   • Transport Mandate: Children receiving racemic epinephrine must be observed for a minimum mandatory period of 2 to 4 hours post-administration before determining disposition or embarking on transport. Transport teams must carry readily accessible racemic epinephrine and nebulizer kits in the aircraft or ambulance cabin for immediate redosing if stridor returns in transit.

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Acute Epiglottitis (Supraglottitis)

Acute epiglottitis is a fulminant, life-threatening bacterial cellulitis of the supraglottic structures, including the epiglottis, arytenoids, aryepiglottic folds, and vallecula.

• Etiology: Historically driven by Haemophilus influenzae type b (Hib) in toddlers aged 2 to 6 years. With widespread Hib vaccination, the overall incidence has decreased, and cases now occur across older children and adolescents, driven by Streptococcus pneumoniae, Group A Streptococcus (Streptococcus pyogenes), and Staphylococcus aureus (including MRSA).
• Clinical Hallmarks: Abrupt onset (often within 6 to 12 hours) of high fever (> 39°C), toxic appearance, severe odynophagia, refusal to swallow, and active drooling. Phonation is muffled with a characteristic "hot potato" voice (dysphonia), but a barking cough is characteristically absent.
• Postural Sign: The child spontaneously assumes the "tripod position" (sitting upright, leaning forward, hands braced on knees, neck hyperextended, and chin thrust forward in the "sniffing" posture) to physically maximize supraglottic airway patency.
• Radiography: Lateral soft tissue neck X-ray reveals a massive, swollen, rounded epiglottic shadow projecting into the hypopharynx, known as the "thumbprint sign".

Transport Safety: The "Zero Agitation" Mandate

In suspected epiglottitis, ANY AGITATION CAN TRIGGER COMPLETE, FATAL AIRWAY OBSTRUCTION. Crying increases turbulent airflow, driving dramatic negative intrathoracic pressures that suck the swollen, redundant supraglottic tissues downward into the laryngeal inlet, causing sudden asphyxiation.

Transport Protocol: Strict Zero-Agitation Rules for Epiglottitis

1. Never Inspect the Oropharynx: Do NOT depress the tongue with a tongue blade or examine the posterior pharynx; direct stimulation precipitates immediate fatal laryngospasm.
2. Avoid Noxious Procedures: Defer intravenous line placement, blood draws, and rectal temperatures until the airway is surgically secured.
3. Preserve Position of Comfort: Allow the child to remain upright in the caregiver's lap. Never force the child supine on a transport cot.
4. Passive Oxygen Delivery: Provide humidified oxygen via passive blow-by tubing held gently near the face by the caregiver.
5. Direct Transfer to Operating Room: Transport directly to a tertiary pediatric operating room with advance mobilization of pediatric anesthesiology and pediatric otolaryngology (ENT). Definitive airway control requires controlled inhalational induction (sevoflurane) in the OR, rigid bronchoscopy, and endotracheal intubation using an ETT 0.5 to 1.0 mm smaller than age-predicted size, with surgical tracheostomy instruments open at the bedside.

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Bacterial Tracheitis (Pseudomembranous Croup)

Bacterial tracheitis is an acute, invasive bacterial infection of the subglottic tracheal mucosa, frequently developing as a secondary bacterial superinfection following viral croup or influenza.

• Microbiology: Staphylococcus aureus (most common), Streptococcus pneumoniae, Moraxella catarrhalis, and Group A Streptococcus.
• Pathophysiology: Intense bacterial proliferation produces mucosal necrosis, diffuse ulceration, copious thick purulent secretions, and dense, fibrinous pseudomembranes that loosely adhere to the tracheal wall.
• Clinical Distinction: Presents as a child with apparent viral croup who suddenly develops high fever, toxic prostration, severe biphasic stridor (both inspiratory and expiratory), and thick, copious secretions that are completely refractory to nebulized racemic epinephrine and dexamethasone.
• Transport Management: Sloughed pseudomembranes present an extreme hazard of sudden luminal tracheal occlusion. Transport teams must prepare for immediate endotracheal intubation under direct laryngoscopy. Once intubated, aggressive tracheal suctioning and bronchoscopic toilet are vital to clear purulent membranes. Empiric broad-spectrum parenteral therapy (Ceftriaxone 50 mg/kg IV + Vancomycin 15 mg/kg IV) must be initiated without delay.

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Foreign Body Airway Obstruction (FBAO)

Foreign body aspiration occurs most commonly in children aged 1 to 3 years due to immature dentition, oral exploratory behavior, and incomplete coordination of swallowing and laryngeal closure. Common aspirated materials include peanuts, grapes, hot dogs, coins, and small toy parts.

• Pathophysiology: Foreign bodies typically lodge in the larynx, trachea, or right mainstem bronchus (which has a steeper angle and wider diameter than the left). Obstruction may be complete, or partial with a ball-valve mechanism where air enters around the object during inspiration (negative intrathoracic pressure widens airways) but becomes trapped during expiration (positive pressure narrows airways).
• Clinical Signs: Sudden, witnessed choking, paroxysmal coughing, gagging, or cyanosis while eating or playing, followed by focal unilateral wheezing, asymmetrical chest expansion, and unilaterally diminished breath sounds without prior fever or URI prodrome.
• Imaging: Bilateral decubitus or inspiratory-expiratory chest radiographs demonstrate unilateral air trapping (hyperinflation, hyperlucency, and mediastinal shift away from the affected side during expiration) or localized atelectasis.

Transport Resuscitation Algorithm for FBAO

• Responsive Infant (< 1 year old): Support the infant prone along the rescuer's forearm with the head angled downward; deliver 5 firm back blows (slaps) between the scapulae. Turn the infant supine and deliver 5 chest thrusts with the heel of one hand over the lower half of the sternum (2025 AHA). Repeat until the object is dislodged or the infant loses consciousness. Never perform blind finger sweeps, which can push the foreign body deeper into the subglottic space.
• Responsive Child (> 1 year old): The 2025 AHA guidelines use repeated cycles of 5 back blows followed by 5 abdominal thrusts (inward and upward, from behind the child) until the object is expelled or the child becomes unresponsive.
• Unresponsive Pediatric Patient: Lower the patient to the stretcher, activate emergency support, and initiate high-quality CPR starting with chest compressions. Each time the airway is opened to deliver breaths, look inside the mouth; if the foreign object is directly visualized, gently retrieve it. If ventilation remains impossible, perform direct laryngoscopy immediately and use Magill forceps to grasp and extract the foreign body under direct vision.

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Diagnostic Differential of Acute Upper Airway Obstruction

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Realistic Transport Scenario: In-Flight Rebound Croup Following Racemic Epinephrine

A critical care transport team is dispatched via rotor-wing aircraft to transfer an 18-month-old child (weight 11 kg) with severe croup from a community emergency center to a pediatric ICU. At the referring hospital, the patient presented with Westley Croup Score of 8 (stridor at rest, marked retractions, decreased air entry). The referring physician administered 0.5 mL of 2.25% racemic epinephrine via nebulizer and 6.6 mg of dexamethasone IV. Within 30 minutes, the child's stridor vanished, retractions resolved, and room air SpO2 stabilized at 98%.

Seventy-five minutes later, while cruising at 2,500 feet above ground level, the child awakens, cries, and abruptly develops severe harsh inspiratory stridor, suprasternal retractions, and agitation. Pulse oximetry falls to 89% on room air, and heart rate accelerates to 175 bpm. The transport nurse recognizes racemic epinephrine rebound phenomenon due to waning alpha-adrenergic vasoconstriction. The team immediately connects a second dose of 0.5 mL racemic epinephrine (in 3 mL normal saline) to an in-line nebulizer powered by 6 L/min oxygen. The nurse delivers blow-by nebulization while the flight paramedic positions the child upright on the mother's lap. Within 15 minutes, the stridor softens, retractions remit, and SpO2 recovers to 97%, allowing uneventful arrival at the tertiary center without invasive airway placement.

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Clinical Pearls for Pediatric Upper Airway Obstruction