Lucan · Conditions

Paediatric airway emergencies (dangerous causes of upper airway obstruction)

Australian guidance: RCH Melbourne CPG — Acute Upper Airway Obstruction + Foreign Bodies Inhaled; ASCIA Anaphylaxis Guidelines; ACSQHC Acute Anaphylaxis Clinical Care Standard; Australian Immunisation Handbook — Haemophilus influenzae type b (Hib)

1. Definition and epidemiology

"Paediatric airway emergencies" as used here refers to the group of conditions that present with acute or chronic stridor and/or respiratory distress in an infant or child and that must be actively excluded before a presentation is safely labelled as simple viral croup, by far the most common cause and covered in a separate topic file. This file is deliberately a discrimination-focused "dangerous mimics" file: acute epiglottitis, bacterial tracheitis, an inhaled foreign body, anaphylaxis with airway involvement, and retropharyngeal abscess are individually much less common than croup but disproportionately responsible for paediatric airway deaths, because each can progress from first presentation to complete obstruction within hours, or less, if the diagnosis is missed or the child is handled incorrectly. Laryngomalacia is included for contrast: it is the most common cause of stridor in infancy, it is benign, and correctly recognising it prevents an unnecessary emergency work-up in a well baby.

The epidemiology of these conditions in Australia has been transformed by immunisation. Before Haemophilus influenzae type b (Hib) vaccination was introduced into the National Immunisation Program in 1993, Hib caused more than 95 percent of childhood epiglottitis; invasive Hib disease, including epiglottitis and meningitis, is now rare in fully immunised children and occurs disproportionately in the unimmunised, the incompletely immunised, and the immunocompromised. This single fact reframes the whole topic: a generation ago, epiglottitis was the emergency every paediatric trainee feared most; today it is rare enough that missing the diagnosis in an unimmunised child, or wrongly reassuring the family of one, is now the greater risk.

2. Pathophysiology

Every condition in this file converges on the same underlying physics. Airflow through the airway is governed, to a first approximation, by Poiseuille's law: resistance to laminar flow is inversely proportional to the radius raised to the fourth power (R is proportional to 1/r^4). A small absolute reduction in radius therefore produces a very large rise in resistance: halving the radius increases resistance sixteen-fold. Because a child's airway starts from a much smaller baseline radius than an adult's, the same absolute millimetre of oedema, pus, foreign material or angio-oedema causes a far greater proportional narrowing, and therefore a far greater rise in resistance, in a small child than the identical pathology would in an adult. This is the master mechanism explaining why children with airway disease can look comparatively well and then deteriorate with frightening speed, and why every condition below is treated with more urgency in a child than the equivalent finding would attract in an adult.

Several anatomical features compound this vulnerability. In the infant, the subglottis (the cricoid ring) rather than the glottis (the vocal cords) is the narrowest point of the airway, and it is the only complete cartilaginous ring in the entire airway; because it cannot expand, oedema or obstruction here narrows a fixed, funnel-shaped space rather than a distensible one. The tongue is relatively large for the size of the oral cavity and mandible, predisposing to posterior airway obstruction, particularly with reduced consciousness, sedation or anaesthetic induction. The epiglottis is floppier, more omega-shaped, and more posteriorly angled than in the adult, and the larynx itself sits more cephalad and anterior, roughly opposite the third or fourth cervical vertebra rather than the fifth or sixth as in the adult, which is one reason paediatric laryngoscopy is a distinct technical skill rather than a scaled-down version of the adult technique. The trachea is short (only a few centimetres in a neonate, compared with around 12 cm in an adult), so there is little margin for error with endotracheal tube position or neck movement, and any obstructing lesion has a much shorter distance to travel to critically compromise the entire airway. Finally, infants and young children have a higher metabolic rate and oxygen consumption relative to body mass, combined with a lower functional residual capacity, so their oxygen reserve is exhausted rapidly once ventilation is compromised or apnoea occurs. Together, these features are why the RCH Melbourne Acute Upper Airway Obstruction guideline places such emphasis on involving the most senior clinician available, with anaesthetic or ENT support, as early as possible, rather than waiting for a child to deteriorate before escalating.

3. Clinical presentation and diagnostic criteria

Epiglottitis. Acute inflammatory swelling of the epiglottis and surrounding supraglottic structures, classically caused by Haemophilus influenzae type b in an unimmunised or incompletely immunised child, though other organisms (non-typeable H. influenzae, Streptococcus pyogenes and pneumoniae, Staphylococcus aureus) are increasingly relevant in the post-vaccine era. Onset is rapid, over hours: high fever, systemic illness, a muffled ("hot potato") voice, drooling with pooling of secretions the child will not swallow, dysphagia, and low-pitched stridor or stertor. Cough is characteristically absent — a key discriminator from croup and bacterial tracheitis. The child instinctively sits upright, often leaning forward with the neck extended (a tripod or sniffing posture), to maximise airway patency.

Bacterial tracheitis (pseudomembranous croup). Typically arises when Staphylococcus aureus (occasionally Streptococcus pyogenes, Streptococcus pneumoniae, or non-typeable H. influenzae) superinfects an airway already inflamed by a preceding viral illness that looked like ordinary croup for a day or two. The result is thick purulent tracheal secretions and, in severe cases, a sloughed pseudomembrane that can itself obstruct the airway. The child becomes systemically unwell with rapidly progressive symptoms: high fever, toxic appearance, a markedly tender trachea, and a cough that is productive of thick secretions rather than the classic dry bark of croup. Critically, these children show little or no improvement with nebulised adrenaline that would settle simple croup, which is one of the most useful bedside discriminators between the two.

Inhaled foreign body. The vast majority of inhalation events occur in children under four years old. The history is a witnessed or unwitnessed episode of choking, coughing or gagging while eating (nuts, seeds, grapes and other foods are classic) or playing with a small toy part. Signs are focal and asymmetrical: reduced air entry or wheeze confined to one side, which may partially respond to a bronchodilator without this excluding the diagnosis. Most inhaled foreign bodies come to rest in a bronchus rather than the larynx or trachea, and the right main bronchus is the classic site of predilection because it is wider, more vertically oriented, and a more direct continuation of the trachea than the more sharply angulated left main bronchus.

Anaphylaxis with airway involvement. IgE-mediated mast cell and basophil degranulation releases histamine, tryptase and leukotrienes, causing angio-oedema of the lips, tongue, pharynx and larynx alongside bronchospasm, vasodilation and increased vascular permeability. Onset is rapid, typically within minutes of exposure to a food, drug, insect venom or other trigger. Look for stridor and/or voice change occurring together with urticaria, angio-oedema, wheeze, vomiting or haemodynamic compromise, rather than an isolated airway sign.

Retropharyngeal abscess. Suppuration of the retropharyngeal lymph node chain, usually following an antecedent pharyngitis or upper respiratory tract infection; because these nodes involute with age, the condition mainly affects children under about five to six years. Presentation includes fever, neck stiffness or torticollis with reluctance to move or extend the neck, drooling, a muffled voice and odynophagia; severe cases develop stridor and respiratory distress as the airway is compressed from behind. This is consistent with the cross-reference to retropharyngeal and parapharyngeal abscess in the RCH Melbourne Acquired Torticollis guideline, which recommends contrast CT of the neck when the diagnosis is suspected and prompt ENT referral.

Laryngomalacia. The important "this is not an emergency" contrast diagnosis. Congenital laxity of the supraglottic structures — short aryepiglottic folds, a floppy omega-shaped epiglottis, and redundant arytenoid mucosa — causes dynamic collapse of these tissues into the airway on inspiration. It presents in the first weeks of life with chronic, intermittent, positional inspiratory stridor that is worse when supine, feeding, crying or agitated, and improves prone or with neck extension. Critically, the infant is otherwise well, feeding adequately and thriving, and is not toxic, febrile or acutely distressed. Most cases resolve spontaneously by 12 to 24 months as the laryngeal cartilage matures; red flags prompting ENT referral include severe stridor, apnoeic episodes, cyanosis, feeding difficulty or faltering growth.

Discrimination table. The following table contrasts the five acute causes on the features most useful at the bedside.

4. Investigations and AU-specific cutoffs

The overarching principle across every condition in this file is that investigations are deferred until the airway is secure, or until a senior clinician is satisfied that pursuing them will not precipitate deterioration; no child with significant upper airway obstruction should be sent to a radiology department unaccompanied or unmonitored.

In suspected epiglottitis, no examination of the throat, tongue depressor use, or attempt at intravenous cannulation or venepuncture should occur before the airway is secured by a senior anaesthetist in theatre, because instrumentation or agitation can precipitate complete obstruction through laryngospasm or by causing the swollen epiglottis to prolapse across the laryngeal inlet. If a lateral soft-tissue neck radiograph is obtained at all — only when the diagnosis is genuinely uncertain and the child is stable enough to remain accompanied and monitored throughout — the classic finding is the thumbprint sign, a rounded, thickened epiglottic shadow replacing the normal thin, curved epiglottic silhouette. A normal film does not exclude epiglottitis and must never delay securing the airway in a clinically convincing presentation.

Bacterial tracheitis is largely a clinical and bronchoscopic diagnosis: direct laryngoscopy or bronchoscopy in theatre reveals thick purulent secretions and, at times, a sloughed pseudomembrane, and blood tests typically show a marked neutrophilia and elevated CRP once it is safe to take them.

For an inhaled foreign body, inspiratory and expiratory chest radiographs (in a child able to cooperate with breath-holding) or lateral decubitus views in a younger child are used to look for air trapping or failure of the affected side to deflate or collapse. A normal chest radiograph does not exclude an inhaled foreign body: most inhaled objects, particularly organic material, are radiolucent, and demonstrable air trapping may be absent, especially soon after inhalation. Rigid bronchoscopy under general anaesthesia is both the definitive investigation and the treatment.

Anaphylaxis is a clinical diagnosis and no investigation should delay adrenaline administration. Serum tryptase, if the diagnosis is genuinely in doubt, is most informative when taken as close as practical to symptom onset and again at one to two hours, but this never precedes treatment.

Retropharyngeal abscess is suggested by prevertebral soft tissue widening on a lateral neck radiograph, but contrast-enhanced CT of the neck is the definitive investigation, distinguishing a drainable abscess from cellulitis or phlegmon and guiding surgical planning.

5. Management

The general approach to any child with acute upper airway obstruction of uncertain cause comes before any condition-specific step. Allow the child to adopt whatever position they find most comfortable (usually sitting upright on a parent's lap) and actively avoid causing distress; keep the child with their parent or carer throughout, and avoid unnecessary examination, cannulation or separation. Call for the most senior clinician available, with anaesthetic or ENT support, early — before the child has deteriorated to the point of crisis — consistent with the RCH Melbourne Acute Upper Airway Obstruction guideline's instruction to involve senior anaesthetic or ENT support as a core principle rather than a last resort. Nebulised adrenaline may be considered for temporary relief in any life-threatening upper airway obstruction while definitive care is arranged, and dexamethasone 0.6 mg/kg (maximum 16 mg) given intramuscularly, intravenously or orally can be considered to reduce swelling in significant obstruction of undifferentiated cause; neither of these measures ever substitutes for securing the airway when epiglottitis or another fixed, progressive obstruction is suspected.

For suspected epiglottitis, the child is transferred undisturbed, sitting up and accompanied by a parent, directly to theatre for inhalational induction (for example with sevoflurane) and intubation by the most senior anaesthetist available, with ENT present and equipped for emergency tracheostomy should intubation fail. Intravenous access, blood tests and intravenous antibiotics (for example ceftriaxone, covering Hib and the other likely organisms) are deferred until after the airway is secured.

Bacterial tracheitis usually requires intubation, often with direct laryngoscopy or bronchoscopy to clear purulent secretions or a pseudomembrane, together with empirical intravenous antibiotics covering Staphylococcus aureus (for example flucloxacillin, with vancomycin added where there is a risk of MRSA), managed in a paediatric intensive care setting.

For an inhaled foreign body, keep the child calm in a position of comfort; if there is complete obstruction with an ineffective cough or loss of consciousness, standard basic life support choking manoeuvres apply — back blows and chest thrusts in an infant, back blows and abdominal thrusts in an older child — and blind finger sweeps should not be attempted. Definitive management is rigid bronchoscopy for retrieval.

Anaphylaxis is treated with immediate intramuscular adrenaline into the anterolateral thigh, dosed by weight (see section 6). The child should be positioned lying flat, or sitting only if breathing difficulty predominates, and must never be allowed to suddenly stand or sit upright, which is associated with sudden fatal cardiovascular collapse from reduced venous return in the setting of vasodilation. Call for help, repeat intramuscular adrenaline every five minutes if there is no improvement, give oxygen and intravenous fluids for hypotension, and add antihistamines or corticosteroids only as adjuncts once adrenaline has been given.

Retropharyngeal abscess is managed with intravenous antibiotics covering Streptococcus pyogenes, Staphylococcus aureus and oral anaerobes, urgent ENT referral for surgical drainage if a discrete abscess is confirmed on CT or there is no response to antibiotics within 24 to 48 hours, and airway support if there is compromise.

Laryngomalacia in the typical well infant requires reassurance and safety-net advice rather than emergency intervention; referral to ENT for flexible nasendoscopy is appropriate if the diagnosis is uncertain or a red flag is present, with supraglottoplasty reserved for severe cases.

6. Pharmacology and AU PBS notes

Adrenaline (epinephrine) 1:1000 (1 mg/mL) plays two very different roles in this topic, and confusing them is a genuine source of medication error.

For anaphylaxis, the ACSQHC Acute Anaphylaxis Clinical Care Standard sets out weight-based intramuscular dosing given into the mid-anterolateral thigh, at approximately 0.01 mL/kg (0.01 mg/kg), repeated every five minutes if there is no improvement:

There are no absolute contraindications to adrenaline in anaphylaxis, and delayed administration is a recognised risk factor for fatal outcomes; intravenous adrenaline (a different, more dilute preparation given as an infusion) is reserved for clinicians trained in its use in a monitored critical care setting, not for first-line treatment. Personal adrenaline autoinjectors are PBS-subsidised for patients with a history of anaphylaxis or another indication for one.

For upper airway obstruction of the croup type, nebulised adrenaline is used differently: 0.5 mL/kg of 1:1000 solution to a maximum of 5 mL, providing only temporary relief of mucosal oedema and never substituting for definitive airway management when a fixed or progressive obstruction (epiglottitis, bacterial tracheitis, a retained foreign body) is suspected.

Dexamethasone 0.6 mg/kg (maximum 16 mg), given intramuscularly, intravenously or orally, is the dose used in the RCH Melbourne Acute Upper Airway Obstruction guideline to reduce swelling in significant obstruction of any cause; this is a notably higher dose than the 0.15 mg/kg used for uncomplicated croup, reflecting the broader and more severe population the guideline covers.

Ceftriaxone is the standard empirical intravenous antibiotic once the airway is secured in suspected epiglottitis or retropharyngeal abscess, covering Hib and streptococcal species; flucloxacillin (with vancomycin added if MRSA risk is significant) covers the Staphylococcus aureus responsible for most bacterial tracheitis.

Hib-containing vaccine is funded under the National Immunisation Program (not the PBS) at 2, 4, 6 and 18 months of age, with vaccine effectiveness against invasive Hib disease estimated at around 94 to 96 percent for a complete primary course.

7. Complications and monitoring

Epiglottitis causes complete airway obstruction and death if unrecognised or instrumented before the airway is secured; septic complications including bacteraemia and meningitis can coexist, and the case-fatality rate for invasive Hib disease remains significant even with modern treatment.

Bacterial tracheitis can be just as lethal as epiglottitis if unrecognised, with the additional specific risk of sudden complete obstruction from a dislodged pseudomembrane.

A missed or retained inhaled foreign body can cause post-obstructive pneumonia, atelectasis and, if retained for weeks or longer, bronchiectasis; the classic pitfall is a symptom-free interval after the initial choking episode that falsely reassures both parents and clinicians.

Anaphylaxis can recur as a biphasic reaction hours after apparent resolution, so a period of observation is required after treatment (longer for severe reactions or those needing more than one dose of adrenaline); every child should leave with a personal adrenaline injector prescription, a written action plan, and referral to an allergy specialist.

Untreated retropharyngeal abscess can progress to mediastinitis, airway rupture, or great vessel or jugular venous involvement.

Laryngomalacia has an excellent prognosis in the typical case; ongoing monitoring is limited to growth and feeding, with escalation only if a red flag emerges.

Across every condition above, continuous oxygen saturation monitoring is required once a child is being actively managed for airway compromise, and no such child should be left unmonitored or separated from a carer or clinician until the diagnosis is clarified and the airway risk has passed.

Written for Australian practice and grounded in the guidance named above. Study material only — not medical advice. Always check against current guidelines.