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CROUP (ACUTE LARYNGOTRACHEOBRONCHITIS)

A Comprehensive Evidence-Based Review for DNB/MD Pediatrics Residents

Sources: Cummings Otolaryngology (7e), Scott-Brown's Otorhinolaryngology (Vol 2), Rosen's Emergency Medicine (9e), Barash Clinical Anesthesia (9e), UCSF/Lurie/CHOC/Dell Children's 2024-2025 Guidelines, PubMed systematic reviews (PMID 34397099, 37916233)

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1. DEFINITION AND EPIDEMIOLOGY

• Most common infectious cause of stridor and acute upper airway obstruction in children - accounts for >90% of all pediatric stridor cases
• Annual incidence: 1.5-6% in children under 6 years
• Age: Primarily 6 months to 3 years; peak at ~2 years; rare after 6 years
• Sex: Boys more commonly affected than girls (M:F ~1.4:1)
• Seasonality: Late autumn and winter (coincides with parainfluenza type 1 biennial epidemics in odd-numbered years); minor February peak also documented
• 3-5% of children have at least one episode during childhood
• Hospital admission required: 6-10% of cases
• Critical care services required: 3-10%
• Mortality: Extremely rare (~1 in 30,000 cases)

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2. ETIOLOGY

Viral Causes (>95% of cases)

Bacterial Causes (uncommon)

• Bacterial tracheitis (membranous croup): Staphylococcus aureus (most common), Streptococcus pyogenes, Moraxella catarrhalis, H. influenzae - produces pseudomembranes; far more toxic picture
• Bacterial superinfection following viral croup may occur with H. influenzae or S. aureus

🔴 MUST REMEMBER: Influenza-associated croup is clinically more SEVERE than parainfluenza-associated croup. SARS-CoV-2 Omicron variant is a new etiology of severe croup - added to practice awareness since 2022.

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3. RISK FACTORS

• Age 6 months to 3 years (subglottis anatomically narrow)
• Male sex
• Pre-existing subglottic or tracheal narrowing (congenital subglottic stenosis)
• Chronic lung disease
• Airway hyperreactivity / atopy (inhalant or food allergies)
• Gastroesophageal reflux disease (GERD) - associated with recurrent croup
• Unvaccinated status (for measles-associated croup)
• Previous history of intubation (acquired subglottic stenosis risk)
• Low socioeconomic status / crowded living conditions

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4. RELEVANT ANATOMY AND PATHOPHYSIOLOGY

Why the Subglottis is the Critical Site

• The subglottis (immediately below the vocal cords) is the narrowest part of the pediatric airway
• It is surrounded by the cricoid cartilage, the only complete cartilaginous ring in the trachea
• This rigid, non-expanding ring prevents outward expansion of inflammatory edema - all swelling is directed inward, reducing the airway lumen
• In an 18-month-old child with a subglottic diameter of ~6.5 mm, just 1 mm of edema reduces cross-sectional area by approximately 50%

Why Stridor Occurs - Poiseuille's Law

• Airflow through a tube is proportional to the 4th power of the radius (Poiseuille's law for laminar flow)
• A 50% reduction in radius = 16-fold reduction in airflow
• As airway diameter decreases, turbulent flow replaces laminar flow, producing the characteristic high-pitched inspiratory stridor
• Stridor does NOT occur until obstruction is already significant (>50% luminal compromise) - hence its presence indicates meaningful obstruction
• Biphasic stridor indicates more severe, near-complete obstruction

Pathophysiological Sequence

Viral infection (nasopharynx) → Spread to larynx & trachea → Mucosal inflammation
→ Edema of subglottic mucosa → Narrowing of subglottis (narrowest, rigid ring)
→ Increased airway resistance → Turbulent airflow → STRIDOR
→ Increased work of breathing → Fatigue → Respiratory failure (severe disease)

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5. CLINICAL FEATURES AND TYPICAL PROGRESSION

Prodromal Phase (Days 1-2)

• Low-grade fever
• Coryza, nasal congestion
• Mild sore throat
• Symptoms of upper respiratory tract infection

Acute Phase (Day 2-3 onwards)

1. Hoarse voice (laryngeal involvement)
2. Seal-like / dog-like barking cough (pathognomonic - harsh, resonant, resembles a seal barking)
3. Inspiratory stridor (subglottic obstruction)

• Variable fever (low to moderate; high fever should prompt consideration of bacterial tracheitis or epiglottitis)
• Tachypnea, tachycardia (proportional to obstruction severity)
• Subcostal/intercostal retractions (increased work of breathing)
• Symptoms worse at NIGHT (circadian variations in airway tone, posture, secretions)
• Symptoms worsen with agitation/crying (increased airflow demands)
• Children are NOT toxic in appearance (distinguish from epiglottitis)
• No drooling, no dysphagia, no preference for "tripod" position

Typical Duration

• Cough: average 3 days
• All symptoms typically resolve within 4-7 days
• 50% improve within 24 hours; most recover within 4 days
• 80% resolve within 2 days

Red Flags for Severe Disease

• Biphasic stridor (both inspiratory AND expiratory)
• Stridor at rest
• High fever (suspect bacterial tracheitis)
• Toxic appearance
• Drooling / dysphagia (suspect epiglottitis)
• Cyanosis
• Decreased level of consciousness
• Oxygen desaturation
• Absence of response to standard treatment (consider alternate diagnosis)

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6. DIFFERENTIAL DIAGNOSIS OF STRIDOR

High-Yield Comparison Table

🔴 EXAM PEARL: The single most important distinction: DROOLING + TOXIC APPEARANCE + NO BARKY COUGH = EPIGLOTTITIS (airway emergency - do NOT examine throat, do NOT lie child flat)

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7. CLASSIFICATION OF SEVERITY

A. Westley Croup Score

• Mild: Score 0-2 (some sources: <3)
• Moderate: Score 3-7 (some sources: 3-8)
• Severe: Score 8-11
• Impending respiratory failure: Score ≥12

Note: Score correlates with tracheal lumen diameter on radiology. The score is widely used in research but interobserver variance limits daily clinical use.

B. Clinical Severity Classification (More Practical)

🔴 CRITICAL PITFALL: Decreasing stridor in a deteriorating child does NOT mean improvement - it may indicate exhaustion and impending respiratory arrest (airway too narrow for stridor to be audible). Always assess in conjunction with mental status and work of breathing.

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8. DIAGNOSTIC APPROACH

History

• Age (peak 6 months - 3 years)
• Duration: acute onset of barky cough (usually 1-3 day URI prodrome)
• Symptoms: character of cough, presence/type of stridor, hoarseness, fever, drooling
• Time course: gradual (viral) vs. rapid (epiglottitis/bacterial tracheitis)
• Vaccination history (measles, Hib vaccines)
• Previous episodes (recurrent croup → consider subglottic stenosis, GERD, allergy)
• Possible foreign body ingestion/aspiration
• Allergies, medications (anaphylaxis)
• Response to previous treatment

Physical Examination

1. General appearance: toxic vs. non-toxic; level of consciousness
2. Work of breathing: retractions (type and severity), tachypnea
3. Stridor: inspiratory only vs. biphasic; at rest vs. with agitation
4. Air entry bilaterally
5. Heart rate, SpO2 (if feasible without distressing child)
6. Color: pink vs. pallor vs. cyanosis
7. Voice quality: hoarse (croup) vs. muffled (epiglottitis/peritonsillar)

⚠️ BEDSIDE TIP: Minimize examination of the oropharynx in moderate-severe croup; any distress/agitation worsens obstruction. NEVER force the child to lie flat or hold them against their will.

Investigations

• Diagnosis is purely clinical
• Radiographs do NOT change management in typical croup
• Viral testing is NOT routinely recommended
• Laboratory tests (CBC, CRP) are NOT routinely indicated

• Atypical presentation (infant <6 months, unusually severe, fails standard treatment)
• Diagnostic uncertainty (rule out epiglottitis, foreign body, bacterial tracheitis)
• Frequent recurrent episodes (consider endoscopy)
• Immunocompromised patient

Role of Neck X-ray and the Steeple Sign

• Diagnostic uncertainty (? epiglottitis vs. croup vs. FB)
• Severe disease not responding to treatment
• Atypical features
• NOT routine for typical croup

• Appearance: Loss of normal "shouldering" of subglottis; tracheal air column tapers to a symmetric point ("steeple" or "church steeple" shape) or "pencil tip"
• View: Anteroposterior (AP) - best view
• Steeple sign is ABSENT in 50% of croup cases
• Steeple sign is NOT pathognomonic - may be seen in normal children
• In epiglottitis: AP shows "thumb sign" (enlarged, rounded epiglottis); lateral shows obliteration of vallecula

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9. EVIDENCE-BASED MANAGEMENT ACCORDING TO SEVERITY

General Principles (All Severities)

• Keep child CALM - agitation worsens obstruction
• Keep child WITH PARENT/CAREGIVER at all times
• Minimize unnecessary procedures and examinations
• Avoid separating child from caregivers
• Avoid sedatives (risk of respiratory depression)
• Position of comfort (upright, in parent's lap)
• Pulse oximetry: only if it does not distress child; NOT routinely recommended

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MILD CROUP (Westley Score 0-2; Intermittent barky cough, no stridor at rest)

• Reassurance of parents and child
• Dexamethasone 0.15 mg/kg oral (single dose; max 10-16 mg) - evidence supports use even in mild croup (reduces return visits, duration, subsequent severity)
• Note: Some guidelines (UCSF 2024) recommend dexamethasone for ALL patients with croup regardless of severity
• Discharge home with return precautions
• No nebulized epinephrine required
• No humidified air/steam - not evidence-based
• Education: symptoms worsen at night, return if: stridor at rest, increased work of breathing, worsening distress

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MODERATE CROUP (Westley Score 3-7; Stridor at rest, retractions)

• Minimize agitation; allow child to remain with parent
• Dexamethasone 0.6 mg/kg oral or IM (max 10-16 mg) - single dose
• Nebulized Epinephrine (racemic or L-epinephrine) - see drug section for doses
• Oxygen: only if SpO2 <90-92% (significant hypoxia in moderate croup is RARE; if present, consider alternate diagnosis)
• Observe in ED for minimum 2 hours after epinephrine administration
• If improved after 2-hour observation: discharge with return precautions
• If not improved or worsening: consider repeat epinephrine dose, admit

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SEVERE CROUP (Westley Score 8-11; Marked stridor/retractions at rest, distressed)

• Urgent intervention required; minimize agitation
• Nebulized Epinephrine - administer immediately
• Dexamethasone 0.6 mg/kg IV/IM if cannot take orally
• Supplemental Oxygen if SpO2 <90-92%
• Consider HFNC or Heliox if available
• Observe for 4-6 hours minimum; admit if any persistent symptoms
• PICU involvement; prepare for potential intubation
• Repeat nebulized epinephrine every 20-30 minutes if needed

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IMPENDING RESPIRATORY FAILURE (Westley Score ≥12; Hypoxia, altered sensorium, absent/decreasing stridor)

• Immediate airway management priority
• Call anesthesia/PICU immediately
• Intubation - see indications below
• Controlled intubation in OR preferred (spontaneous breathing maintained if possible)
• Nebulized epinephrine as a temporizing measure while preparing for intubation
• High-flow oxygen, CPAP/HFNC if available
• IV access; IV dexamethasone 0.6 mg/kg
• Do NOT agitate the child while preparing for intubation

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10. DETAILED DISCUSSION OF MEDICATIONS

A. DEXAMETHASONE (First-Line Steroid)

🔴 EXAM PEARL: The IV formulation of dexamethasone (4 mg/mL) can be given ORALLY - no need for injection in most cases. Oral administration is as effective as IV/IM.

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B. NEBULIZED BUDESONIDE

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C. NEBULIZED EPINEPHRINE (ADRENALINE) - HIGH-YIELD DRUG

Racemic Epinephrine vs. L-Epinephrine

• Dose: 0.5 mL/kg of 1:1000 solution (max 5 mL) diluted in 3 mL NS
• Some protocols: flat dose of 5 mL of 1:1000 nebulized (for children > ~10 kg)

Mechanism of Action

• Alpha-1 adrenergic effect: vasoconstriction → reduces mucosal congestion and edema
• Beta-2 adrenergic effect: bronchodilation (minor role in croup)
• Net effect: rapid reduction in subglottic edema → rapid relief of obstruction

Pharmacokinetics in Croup

🔴 CRITICAL EXAM POINT - REBOUND PHENOMENON:

• After nebulized epinephrine, symptoms may return to PRE-TREATMENT baseline at ~2 hours
• This was historically thought to be a worsening/"rebound" - it is NOT
• Current evidence: there is NO true rebound below baseline (UCSF CDSS guidelines, 2024)
• Observation for minimum 2 hours post-epinephrine is therefore required before discharge
• If symptoms resolve and patient is stable after 2 hours of observation → safe to discharge
• Multiple doses may be required in severe cases; ≥4 doses in 8-12 hours should prompt consideration of alternative diagnosis

When to Observe After Epinephrine

• Minimum 2 hours observation after last dose before discharge consideration
• 3-4 hours in more severe cases or if close follow-up uncertain

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D. OXYGEN THERAPY

• Indication: SpO2 <90% (some protocols <92%)
• IMPORTANT: Hypoxia in croup is UNCOMMON in mild or moderate disease
• Significant hypoxia should prompt consideration of an alternative diagnosis or concurrent lower airway disease
• Delivery: blow-by, face mask, or nasal prongs (least distressing method)
• Continuous pulse oximetry NOT routinely recommended (distresses child)

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E. HIGH-FLOW NASAL CANNULA (HFNC) AND CPAP

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F. INDICATIONS FOR INTUBATION AND MECHANICAL VENTILATION

• Respiratory arrest or near-arrest
• Progressive hypoxia despite maximal non-invasive therapy (SpO2 persistently <90%)
• Decreasing level of consciousness / severe exhaustion
• Complete airway obstruction

• Failure of 2-3 doses of nebulized epinephrine
• Severe disease with worsening despite dexamethasone and epinephrine
• Inability to maintain airway patency

• Controlled intubation in operating room (OR) preferred
• Spontaneous breathing maintained (inhalational induction with sevoflurane preferred)
• Endotracheal tube size: at least 0.5-1 mm SMALLER than estimated for age (subglottic narrowing)
• Have a range of tube sizes available (0.5-1 mm smaller than expected)
• Extubation: when air leak is detected around tube
• If no air leak after 5-7 days: endoscopic airway evaluation indicated

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G. TREATMENTS WITHOUT EVIDENCE (OUTDATED PRACTICES)

🔴 COMMON PITFALL: Steam inhalation is still widely practiced in India and resource-limited settings. It has NO evidence of benefit and carries a real risk of scalds/burns. Educate parents to stop this practice.

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11. ADMISSION CRITERIA, PICU INDICATIONS, DISCHARGE CRITERIA, AND FOLLOW-UP

Admission Criteria

• Severe croup (Westley ≥8)
• Persistent moderate croup after dexamethasone and epinephrine
• Continued stridor at rest despite therapy
• Need for supplemental oxygen
• Inadequate oral hydration
• Age <6 months (higher risk of severe disease)
• Atypical presentation / concern for alternative diagnosis
• Social factors: inability to return to care if worsens, caregiver unable to recognize warning signs
• History of intubation or previous severe croup episode

PICU Indications

• Persistent severe croup despite full ED therapy
• Impending or actual respiratory failure
• Requirement for intubation and mechanical ventilation
• Hemodynamic instability
• SpO2 persistently <90% despite oxygen therapy

Discharge Criteria

• No stridor at rest
• No/minimal chest wall retractions
• Normal (or near-normal) mental status
• Normal color; SpO2 adequate
• No severe airway obstruction signs
• Taking oral fluids
• Noticeable improvement after at least 2 hours of observation
• Parents understand return precautions and able to access care

Discharge Instructions (Return Precautions)

• Stridor occurs or worsens at rest
• Increased work of breathing
• Croupy cough lasts >14 days
• Child becomes listless/unresponsive
• Cyanosis

Follow-Up

• Routine follow-up at 24 hours recommended
• Recurrent croup (≥3 episodes): refer for further evaluation (laryngoscopy, pH probe study for GERD)

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12. COMPLICATIONS

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13. PROGNOSIS

• Croup is overwhelmingly a self-limited illness
• 85% have mild disease managed at home
• 50% improve within 24 hours; most within 4 days
• Hospitalization: 6-10%; Critical care: 3-10% of hospitalized
• Mortality: ~1 in 30,000
• Recurrent croup (5% of children): associated with atopy, GERD, congenital subglottic narrowing
• History of croup doubles the odds of subsequent asthma and wheezing
• Long-term prognosis: excellent; no lasting respiratory sequelae in the vast majority

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14. RECENT UPDATES AND CHANGES IN MANAGEMENT (2022-2025)

1. SARS-CoV-2 Omicron as a croup etiology: The BA.2 subvariant has been associated with severe and life-threatening croup in children (PMID 35726145, 2022). COVID-19-associated croup should be considered in unvaccinated or recently COVID-exposed children.
2. Dexamethasone for ALL severities: UCSF and other major centers' 2024 guidelines now recommend dexamethasone for ALL patients with croup regardless of severity (even mild), citing evidence of reduced return visits and disease burden.
3. Abandonment of "rebound" observation myth: Current guidelines clarify that nebulized epinephrine does NOT cause a rebound BELOW baseline severity. The 2-hour observation is to ensure improvement is maintained, not to watch for a paradoxical worsening.
4. No routine X-rays: Major centers explicitly de-emphasize X-ray use; Rosen's and UCSF guidelines 2024 state radiographic studies do not change management and are not sensitive or specific.
5. Heliox - Limited role: Cochrane systematic review (PMID 34397099, 2021) found insufficient data to support routine heliox use; it may serve as a bridge in severe cases.
6. HFNC emerging evidence: Growing use of HFNC in severe croup as a non-invasive modality to reduce work of breathing before intubation.
7. Continuous pulse oximetry NOT routinely recommended: Major institutions caution that routine oximetry monitoring distresses the child and worsens symptoms; reserve for severe disease only.
8. COVID-19 impact on seasonality: Parainfluenza seasonality has been disrupted; rhinovirus and SARS-CoV-2 now contribute to year-round croup presentations.

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15. EMERGENCY DEPARTMENT MANAGEMENT ALGORITHM

CHILD PRESENTS WITH BARKY COUGH, STRIDOR, HOARSENESS
                         |
            ┌────────────────────────┐
            │  Is this CROUP?        │
            │  Rule out:             │
            │  • Epiglottitis        │
            │  • Foreign body        │
            │  • Bacterial tracheitis│
            └────────────────────────┘
                         |
         Atypical features? → Investigate / Senior review
                         |
              ASSESS SEVERITY
     (Westley Score + Clinical Assessment)
                         |
    ┌────────────────────┼────────────────────┐
    |                    |                    |
 MILD               MODERATE              SEVERE/
(Score 0-2)        (Score 3-7)          IMPENDING FAILURE
    |                    |              (Score ≥8/≥12)
    |                    |                    |
Reassurance         Minimize           EMERGENCY:
Dexamethasone       agitation          Call PICU/Anaesthesia
0.15-0.6 mg/kg                         ↓
oral x1 dose        Dexamethasone      O2, IV access
                    0.6 mg/kg          Neb. Epinephrine
Discharge with      oral/IM x1         Dexamethasone
return              dose               0.6 mg/kg IV/IM
precautions                            ↓
                    Neb. Epinephrine   Consider HFNC/CPAP
                    (racemic/L-epi)    ↓
                         |             Prepare for
                    Observe 2 hrs      intubation if:
                         |             • No improvement
                  ┌──────┴──────┐      • SpO2 still <90%
                  |             |      • Altered sensorium
               Improved    Not improved
                  |             |
              Discharge    Repeat epi;
              (if meets    Admit / PICU
              criteria)

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16. IMPORTANT MNEMONICS

Etiology - "PAIR M"

• P - Parainfluenza (types 1, 2, 3) - MOST COMMON
• A - Adenovirus
• I - Influenza A and B (more SEVERE)
• R - RSV (Respiratory Syncytial Virus), Rhinovirus
• M - Measles, Metapneumovirus, Mycoplasma (rare)

Clinical Triad - "BHS"

• B - Barky seal-like cough
• H - Hoarse voice
• S - Stridor (inspiratory)

Management by Severity - "DOME"

• D - Dexamethasone (all severities)
• O - Oxygen (if SpO2 <90%)
• M - Minimize disturbance/agitation
• E - Epinephrine nebulized (moderate-severe)

Westley Score Parameters - "SCACI"

• S - Stridor (0-2)
• C - Chest retractions (0-3)
• A - Air entry (0-2)
• C - Cyanosis (0-5)
• I - Intelligence/consciousness level (0-5)

Differentiating Croup vs. Epiglottitis - "CROUP vs. DROOL"

• CROUP: Cough barky, Rhino prodrome, Own quiet position (upright), Unwell mildly, Parainfluenza
• DROOL: Drooling, Rapid onset, Obstruction severe, Older child (post-Hib era), Leaning forward (tripod)

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17. HIGH-YIELD SUMMARY TABLES

Table 1: Drug Doses Quick Reference

Table 2: Severity-Management Summary

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18. DNB/MD EXAMINATION PEARLS, VIVA QUESTIONS, AND HIGH-YIELD MCQs

Must-Remember Facts (Viva/Theory)

🔴 TOP 10 MUST-REMEMBER FACTS:

1. Croup is the MOST COMMON infectious cause of stridor in children (>90% of stridor cases)
2. Most common causative agent: Parainfluenza virus type 1
3. Classic triad: BARKY cough + HOARSENESS + INSPIRATORY STRIDOR
4. Children with croup do NOT drool, do NOT look toxic, do NOT prefer tripod position - distinguish from epiglottitis
5. Steeple sign may be ABSENT in 50% of croup; X-ray is NOT routinely needed
6. Stridor does NOT occur until >50% reduction in airway cross-sectional area
7. Decreasing stridor + worsening child = EXHAUSTION (emergency) - NOT improvement
8. Dexamethasone oral is as effective as IV/IM; IV formulation CAN be given orally
9. There is NO true rebound below baseline after nebulized epinephrine
10. Steam inhalation has NO evidence and carries burn risk - discourage actively

Viva Questions with Model Answers

High-Yield MCQs

• (A) Epiglottitis (B) Viral Croup ✓ (C) Foreign body aspiration (D) Bacterial tracheitis

• (A) RSV (B) Influenza A (C) Parainfluenza type 1 ✓ (D) Rhinovirus

• (A) IV antibiotics (B) Nebulized salbutamol (C) Oral dexamethasone + nebulized epinephrine ✓ (D) Humidified air

• (A) Widened prevertebral space (B) Enlarged epiglottis (C) Subglottic narrowing ✓ (D) Retropharyngeal widening

• (A) 0.05 mL/kg (B) 0.5 mL/kg (max 5 mL) ✓ (C) 5 mL/kg (D) 1 mL/kg

• (A) IV form cannot be given orally (B) Dose must be repeated daily for 3 days (C) It is ineffective in mild croup (D) Single oral dose is as effective as IV/IM ✓

• (A) 30 minutes (B) 1 hour (C) 2 hours ✓ (D) 6 hours

• (A) Discharge (improvement noted) (B) Repeat chest X-ray (C) Urgent airway management - impending failure ✓ (D) Start antibiotics

• (A) Dexamethasone (B) Nebulized racemic epinephrine (C) Steam inhalation ✓ (D) Nebulized budesonide

• (A) H. influenzae type B (B) Streptococcus pneumoniae (C) Staphylococcus aureus ✓ (D) Moraxella catarrhalis

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QUICK REFERENCE CARD (High-Yield Tables)

Etiology Memory Table

Common Pitfalls Table

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