Pediatric Respiratory: Bronchiolitis, Croup & Epiglottitis
A high-yield Step 2 CK comparison of the three classic pediatric airway infections — bronchiolitis, croup, and epiglottitis — organized by age, buzzwords, imaging signs, and next-best-step management. Emphasizes the board traps: supportive-only care for bronchiolitis and the do-not-examine-the-throat airway emergency of epiglottitis.
Localize the obstruction first
Pediatric stridor and wheeze are high-yield because the boards test whether you can localize the airway obstruction and choose the next step before any imaging. Bronchiolitis is a lower-airway (bronchiole) disease causing expiratory wheezing in infants. Croup (laryngotracheobronchitis) and epiglottitis both cause upper-airway inspiratory stridor — but croup is subglottic, viral, and benign, whereas epiglottitis is supraglottic and a true airway emergency. Three splits crack almost every vignette: the child's age, whether there is a barking cough versus drooling, and whether the child looks toxic. Nail those and both the diagnosis and the management fall out — including the classic 'do-not-touch-the-throat' epiglottitis trap.
- Bronchiolitis: RSV; age <2 yr (peak 2–6 mo), winter; URI prodrome then wheezing + crackles, tachypnea, retractions; apnea in young/premature infants
- Croup: parainfluenza; age 6 mo–3 yr, fall; barking/seal-like cough, inspiratory stridor, hoarse voice, worse at night; low-grade fever, nontoxic
- Epiglottitis: H. influenzae type b (unimmunized/incomplete); age 3–7 yr; abrupt high fever, drooling, tripod posture, muffled 'hot-potato' voice, toxic-appearing — cough usually absent
- All three are diagnosed clinically; imaging is confirmatory, not required (epiglottitis is confirmed by direct visualization in the OR)
- Never use a tongue depressor or agitate a suspected epiglottitis — it can precipitate complete airway obstruction
Side-by-side comparison
| Feature | Bronchiolitis | Croup | Epiglottitis |
|---|---|---|---|
| Airway level | Lower (bronchioles) | Subglottic | Supraglottic |
| Classic pathogen | RSV | Parainfluenza | H. influenzae type b |
| Typical age | <2 yr | 6 mo–3 yr | 3–7 yr |
| Hallmark | Wheeze + crackles | Barking cough, stridor | Drooling, stridor, toxic |
| Cough | Yes | Barky | Usually none |
| Voice | Normal | Hoarse | Muffled 'hot-potato' |
| Fever | Low | Low | High |
| X-ray sign | Hyperinflation | Steeple sign (AP) | Thumbprint sign (lateral) |
| First move | Supportive / O2 | Dexamethasone ± racemic epi | Secure airway + ceftriaxone |
Vignette: A 5-month-old in December has 2 days of rhinorrhea and cough, now with tachypnea, subcostal retractions, and diffuse wheezes and crackles; SpO2 is 91%.
Diagnosis: Bronchiolitis (RSV).
Next best step: Supportive care — nasal suctioning, hydration, and supplemental O2 to keep SpO2 ≥90%. Do not reflexively give albuterol, corticosteroids, or antibiotics, and skip routine CXR and RSV testing — none change outcomes. Admit for apnea, hypoxia, or poor feeding/dehydration. Prevent with nirsevimab (monoclonal Ab given to essentially all infants <8 mo entering their first RSV season) or palivizumab (reserved for high-risk infants — prematurity, chronic lung/heart disease); maternal RSV vaccination in pregnancy is an alternative.
Vignette: A 2-year-old in autumn has 1 day of URI symptoms and now a night-time barking, seal-like cough, hoarse voice, and low-grade fever, with inspiratory stridor only when upset. He is well-appearing with no stridor at rest and no retractions.
Diagnosis: Croup (laryngotracheobronchitis).
Next best step: A single dose of dexamethasone (0.6 mg/kg) for all severities. If there is stridor at rest or respiratory distress, add nebulized racemic epinephrine and observe ≥3–4 hours for rebound before discharge. An AP neck film showing the steeple sign supports the diagnosis but is not required.
Vignette: A 4-year-old with incomplete immunizations has abrupt high fever, sits leaning forward in the tripod position, is drooling, has a muffled voice and soft stridor, and appears toxic and anxious.
Diagnosis: Epiglottitis — an airway emergency.
Next best step: Keep the child calm with a parent; do NOT examine the throat, place an IV/labs, or lay the child supine — any agitation can trigger complete obstruction. Take the child to the OR for controlled intubation by anesthesia/ENT with a surgical-airway backup, then give IV ceftriaxone (add vancomycin to cover MRSA). A lateral neck film (thumbprint sign) is obtained only if the airway is stable — airway comes first.
- Epiglottitis = the 'D's': Drooling, Dysphagia, Distress (± Dysphonia/muffled voice) — plus high fever and the tripod lean
- Imaging signs: a Steeple rises like a church tower in the subglottic airway = Croup; a Thumbprint on the lateral film = epiglottiTis (the swollen epiglottis)
- 'Croup barks, epiglottitis drools' — a barking cough that is worse at night is croup; a quiet, drooling, toxic child is epiglottitis until the airway is secured
- Bronchiolitis: supportive only — O2 for SpO2 <90%, nasal suctioning, hydration; NO routine albuterol, steroids, or antibiotics (classic distractor answers)
- Croup: dexamethasone for everyone; add racemic epinephrine only if stridor at rest, then watch for rebound before discharge
- Epiglottitis: airway first in the OR, then ceftriaxone (± vancomycin for MRSA); never a tongue blade; give rifampin prophylaxis to household contacts of invasive Hib disease when an incompletely-vaccinated child <4 yr is in the home
- Board traps: ordering albuterol or steroids for bronchiolitis, or performing a throat exam in suspected epiglottitis — both are wrong-answer magnets
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