Pediatric Respiratory Disorders

Learning Objectives

By the end of this topic, you should be able to:

• Differentiate bronchiolitis, croup, and epiglottitis by age group, causative organism, and clinical signs
• Describe the pathophysiology and stepwise management of acute asthma exacerbations in children
• Recognize the clinical features that distinguish viral from bacterial pneumonia in children
• Identify RSV as the leading cause of bronchiolitis and explain why bronchodilators are not routinely recommended for it
• Apply the modified Westley croup score concept to judge severity and choose treatment (steroids vs. nebulized epinephrine)
• Recall red-flag signs of respiratory distress in infants and young children that demand urgent escalation

Quick Answer

Pediatric respiratory disorders are conditions of the airway and lungs that behave differently in children than in adults because a child's airway is smaller, more collapsible, and more reactive. The four you must master for exams are bronchiolitis (RSV infection of the small airways in infants under 2, causing wheeze), croup (viral laryngotracheobronchitis causing a barking cough and stridor, typically ages 6 months–3 years), asthma (chronic airway inflammation and hyperreactivity presenting with recurrent wheeze, cough, and breathlessness), and pneumonia (lung parenchymal infection, viral in younger children, more often bacterial with lobar signs in older children). They matter because respiratory illness is the single most common reason young children are brought to a doctor or admitted to hospital, and telling these conditions apart quickly changes management and can be life-saving.

Core Content

Bronchiolitis

Bronchiolitis is inflammation and mucus plugging of the bronchioles — the smallest airways before the alveoli — almost always caused by a virus.

• Who gets it: Infants and children under 2 years, peak incidence at 3–6 months. It is the most common lower respiratory tract infection in infancy.
• Cause: Respiratory syncytial virus (RSV) accounts for the large majority of cases; other viruses (rhinovirus, human metapneumovirus, parainfluenza) can also cause it.
• Why infants specifically: Their airways are already narrow, so even mild mucosal swelling and mucus dramatically increases airway resistance (resistance rises with the fourth power of the reduction in radius).
• Clinical picture: Starts as a viral coryza (runny nose, mild fever) for 1–3 days, then progresses to cough, tachypnea, wheeze, and widespread fine crackles. Feeding difficulty and dehydration are common because a blocked nose and fast breathing make sucking hard.
• Diagnosis: Clinical — history and examination are usually enough. Nasopharyngeal swab for RSV and chest X-ray are reserved for atypical presentations or if severe/unclear diagnosis, not for routine cases.
• Treatment: Supportive only — nasal suction, maintaining hydration/feeds, and supplemental oxygen if saturations are low. Bronchodilators, steroids, and antibiotics do not improve outcomes in typical bronchiolitis and are not routinely recommended, because the obstruction is from mucus and edema, not bronchospasm or bacterial infection.
• Prevention: Palivizumab (a monoclonal antibody) or newer long-acting RSV monoclonal antibodies (e.g., nirsevimab) for high-risk infants (prematurity, chronic lung disease, congenital heart disease); good hand hygiene reduces transmission in nurseries.

Croup (Laryngotracheobronchitis)

Croup is viral inflammation of the larynx, trachea, and bronchi that narrows the subglottic airway — the narrowest part of a child's upper airway.

• Who gets it: Ages 6 months to 3 years, peak around age 2, more common in autumn.
• Cause: Parainfluenza virus type 1 is the classic cause; also RSV, influenza, and adenovirus.
• Clinical picture: A preceding cold, then the hallmark triad — a barking (seal-like) cough, inspiratory stridor, and hoarse voice — often worse at night. Symptoms typically improve with cool or humid air exposure.
• Severity assessment: Judged clinically by degree of stridor (at rest vs. only on agitation), chest wall retractions, and level of consciousness — this determines whether treatment can be outpatient or needs admission.
• Treatment: A single dose of oral dexamethasone is given for almost all cases, even mild ones, because it shortens illness and reduces hospital visits. Nebulized epinephrine (adrenaline) is added for moderate-to-severe cases to rapidly shrink airway swelling, but it wears off in under 2 hours, so the child must be observed afterward for rebound stridor.
• Key contrast: Unlike epiglottitis, croup has a gradual onset, low-grade fever, and the child usually does not look toxic.

Asthma in Children

Childhood asthma is a chronic disease of airway inflammation and hyperresponsiveness leading to reversible airflow obstruction.

• Pathophysiology: Allergen or irritant exposure triggers airway inflammation, bronchial smooth muscle constriction, and mucus hypersecretion — together these narrow the airway lumen and cause the wheeze and prolonged expiratory phase heard on examination.
• Triggers: Viral infections (the most common trigger in young children), allergens (dust mites, pollen, pet dander), cold air, exercise, and tobacco smoke exposure.
• Clinical picture: Recurrent episodes of wheeze, cough (often worse at night or with exercise), chest tightness, and shortness of breath, with symptom-free periods between episodes — this episodic pattern is what separates asthma from a single infective wheeze.
• Diagnosis: Largely clinical in young children because spirometry needs a cooperative child (usually reliable only from about age 5–6). Spirometry showing an obstructive pattern (reduced FEV1/FVC ratio) that improves after a bronchodilator supports the diagnosis in older children.
• Acute exacerbation management (stepwise): Inhaled short-acting beta-agonist (salbutamol) via spacer as first-line, add oral corticosteroids early to reduce inflammation, and use inhaled ipratropium bromide or IV therapies for severe attacks not responding to initial treatment. Silent chest and exhaustion are late danger signs of a life-threatening attack, not signs of improvement.
• Long-term control: Inhaled corticosteroids are the mainstay of preventer therapy for persistent asthma; short-acting beta-agonists are for symptom relief only, not daily control.

Pneumonia in Children

Pneumonia is infection of the lung parenchyma (alveoli and surrounding tissue), and the likely cause shifts with age.

• Under 5 years: Viruses (RSV, parainfluenza, influenza) are the most common cause overall, but Streptococcus pneumoniae remains the leading bacterial cause and the most important one to identify.
• Over 5 years: Bacterial causes become relatively more common, including Mycoplasma pneumoniae ("walking pneumonia" — a slower onset, dry cough, and often a milder-appearing child than the X-ray suggests).
• Clinical picture: Fever, tachypnea (the single most sensitive sign in young children), cough, chest indrawing/retractions, and grunting in infants. Bacterial pneumonia more often produces high fever, focal chest signs (bronchial breathing, dullness to percussion), and looks like a "sicker" child than viral pneumonia.
• Diagnosis: Clinical assessment plus respiratory rate is usually sufficient in primary care; chest X-ray and inflammatory markers (CRP, white cell count) help when the diagnosis is unclear or the child is unwell enough to need admission.
• Treatment: Amoxicillin is first-line oral therapy for uncomplicated bacterial pneumonia in most children; macrolides (e.g., azithromycin) are used when Mycoplasma or Chlamydophila is suspected, or in penicillin allergy. Viral pneumonia is managed supportively.

Cystic Fibrosis (brief note)

Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene, producing thick, sticky secretions that cause recurrent lung infections, poor weight gain, and eventually bronchiectasis. It is identified through newborn screening and sweat chloride testing, and management centers on airway clearance techniques, CFTR modulator drugs, and treating chronic infections — it is included here because it is a key differential when a child has recurrent chest infections that don't fit a simple infective pattern.

Visual Learning

Key Terms

Term	Definition
Bronchiolitis	Viral infection and inflammation of the bronchioles, mainly in infants under 2, most often caused by RSV
Croup (laryngotracheobronchitis)	Viral inflammation narrowing the subglottic airway, producing barking cough and stridor
Stridor	A harsh, high-pitched sound on inspiration caused by upper airway obstruction
Wheeze	A musical, whistling sound on expiration caused by lower airway narrowing
RSV	Respiratory syncytial virus; the leading viral cause of bronchiolitis in infants
FEV1/FVC ratio	Spirometry measure comparing air exhaled in one second to total exhaled volume; reduced in obstructive disease like asthma
Retractions	Visible pulling-in of the chest wall (sternal, intercostal, subcostal) during breathing, indicating increased work of breathing
CFTR	Cystic Fibrosis Transmembrane conductance Regulator; the gene mutated in cystic fibrosis
Tachypnea	Abnormally fast breathing rate for age; the most sensitive clinical sign of pediatric pneumonia
Silent chest	Absence of wheeze in severe asthma because too little air is moving to generate sound — a medical emergency, not a sign of recovery

Common Mistakes

Misconception 1: "A wheezy infant with a cold has asthma." Why it's wrong: True asthma requires a pattern of recurrent, episodic wheeze with symptom-free intervals; a single wheezy episode in an infant during a viral illness is far more likely to be bronchiolitis or viral-induced wheeze. Correct understanding: Asthma is rarely diagnosed with confidence before age 5, and the diagnosis relies on a recurring pattern over time plus supporting spirometry when the child is old enough to perform it.

Misconception 2: "Bronchodilators should be given to every wheezy or breathless infant." Why it's wrong: In bronchiolitis, the airway obstruction is caused by mucus plugging and mucosal edema, not bronchospasm, so bronchodilators like salbutamol have not been shown to change outcomes and are not routinely recommended. Correct understanding: Management of bronchiolitis is supportive (oxygen, fluids, nasal suction); bronchodilators are reserved for children whose picture suggests reactive airway disease, and even then only if a clear clinical response is documented.

Misconception 3: "Stridor and wheeze mean the same thing and can be used interchangeably." Why it's wrong: They point to obstruction in different places and different diseases — mixing them up leads to misdiagnosis. Correct understanding: Stridor is an inspiratory sound from upper airway narrowing (as in croup or epiglottitis); wheeze is an expiratory sound from lower airway narrowing (as in asthma or bronchiolitis). Listening for which phase of breathing produces the sound tells you where the problem is.

Comparison and Connections

Feature	Bronchiolitis	Croup	Epiglottitis	Asthma (acute exacerbation)
Typical age	Under 2 years	6 months–3 years	2–6 years (rare since Hib vaccine)	Usually over 2 years
Cause	RSV (mainly)	Parainfluenza virus	Haemophilus influenzae type b	Allergen/irritant/viral trigger on inflamed airway
Onset	Gradual, after coryza	Gradual, worse at night	Rapid, hours	Can be rapid
Hallmark sound	Wheeze + fine crackles	Barking cough + stridor	Soft stridor, muffled voice	Wheeze, prolonged expiration
Appearance	Unwell but not toxic	Unwell but not toxic	Toxic, drooling, tripod position	Distressed, tachypneic
First-line treatment	Supportive care	Oral dexamethasone	Emergency airway management	Inhaled salbutamol ± steroids

Practice Questions

Recall

1. What organism most commonly causes bronchiolitis, and what age group does it typically affect? Answer guidance: RSV (respiratory syncytial virus); infants under 2 years, peaking at 3–6 months.
2. Name the classic clinical triad of croup. Answer guidance: Barking cough, inspiratory stridor, and hoarse voice.

Understanding 3. Explain why bronchodilators are not routinely used in bronchiolitis even though the child is wheezing. Answer guidance: The obstruction in bronchiolitis comes from mucus plugging and mucosal edema in the small airways, not smooth-muscle bronchospasm, so drugs that relax airway muscle have little effect on outcomes. 4. Why does tachypnea, rather than fever or cough, serve as the most useful sign of pneumonia in a young child? Answer guidance: Young children cannot reliably describe symptoms, and fever/cough are non-specific; a raised respiratory rate for age is objective, easy to measure, and correlates well with lung involvement, making it the most sensitive clinical marker.

Application 5. A 2-year-old arrives with a barking cough, mild stridor only when crying, and no stridor at rest. How would you manage this child? Answer guidance: This is mild croup — treat with a single dose of oral dexamethasone and observe; nebulized epinephrine is not needed unless stridor occurs at rest or the child shows increasing respiratory distress. 6. A 6-month-old has 3 days of runny nose followed by wheeze, tachypnea, and difficulty feeding, with oxygen saturation of 91%. What is the likely diagnosis and immediate management priority? Answer guidance: Bronchiolitis (likely RSV); the immediate priority is supplemental oxygen and support for hydration/feeding, since saturations below 92% typically warrant admission and oxygen therapy.

Analysis 7. A 4-year-old has sudden-onset high fever, drooling, refusal to lie down, and a soft stridor, but no cough. Compare this presentation with croup and explain why the distinction matters clinically. Answer guidance: This picture suggests epiglottitis, not croup — croup has a gradual onset with a barking cough and low-grade fever, while epiglottitis has abrupt onset, toxic appearance, drooling, and absence of cough due to pain on swallowing. The distinction matters because examining the throat or upsetting a child with suspected epiglottitis can precipitate complete airway obstruction; it needs urgent, calm airway management rather than routine croup treatment. 8. Two children present with wheeze: one is 8 months old with a first-ever episode following a cold, the other is 6 years old with recurrent wheeze episodes over 2 years, each resolving fully between episodes. How would you reason through the different likely diagnoses? Answer guidance: The 8-month-old's single episode following a viral prodrome fits bronchiolitis or viral-induced wheeze, which is common and often does not recur as "asthma." The 6-year-old's recurrent, episodic pattern with full recovery between attacks is classic for asthma, and this child is also old enough for spirometry to support the diagnosis.

FAQ

1. Why do infants get bronchiolitis so much more severely than older children get the same virus? Because an infant's airways are already tiny, even a small amount of mucosal swelling dramatically increases resistance to airflow — the same viral infection that gives an older child a mild cold can cause significant breathing difficulty in an infant.

2. Is croup contagious? Yes — it's caused by common respiratory viruses (mainly parainfluenza) spread through respiratory droplets and contaminated surfaces, so normal infection-control precautions (hand hygiene, avoiding close contact) reduce spread.

3. Can a child "grow out of" asthma? Many children with mild, viral-triggered wheeze in early childhood do improve as their airways grow larger and more resistant viral infections; however, children with allergic asthma and a strong family history are more likely to have persistent disease into adulthood.

4. Why is nebulized epinephrine only a temporary fix in croup? It works by causing vasoconstriction that rapidly reduces airway mucosal swelling, but this effect wears off within about 2 hours, so the underlying inflammation is still present — that's why children who receive it must be observed for rebound symptoms before discharge.

5. How is a chest X-ray used differently in bronchiolitis versus pneumonia? In typical bronchiolitis, a chest X-ray is not routinely needed since diagnosis is clinical and X-ray findings (hyperinflation) rarely change management; in suspected pneumonia, especially if the child is unwell or the diagnosis is unclear, an X-ray helps confirm consolidation and rule out complications like effusion.

Quick Revision

• Bronchiolitis = RSV, infants under 2, wheeze + crackles after a cold, treatment is supportive only.
• Croup = parainfluenza virus, ages 6 months–3 years, barking cough + inspiratory stridor + hoarse voice.
• Croup treatment: oral dexamethasone for almost all cases; add nebulized epinephrine for moderate-severe.
• Epiglottitis (rare post-Hib vaccine) = toxic child, drooling, no cough — do not examine the throat.
• Stridor = inspiratory, upper airway problem; wheeze = expiratory, lower airway problem.
• Asthma = chronic airway inflammation + hyperreactivity; diagnosis relies on recurrent episodic pattern, confirmed by spirometry when age allows (~5-6 years+).
• Acute asthma treatment ladder: inhaled salbutamol → add oral corticosteroids early → ipratropium/IV therapy for severe attacks.
• Silent chest in asthma is a danger sign of a life-threatening attack, not improvement.
• Pediatric pneumonia: tachypnea is the most sensitive clinical sign; viruses dominate under age 5, but S. pneumoniae is the key bacterial cause; Mycoplasma is more common over age 5.
• First-line oral antibiotic for uncomplicated bacterial pneumonia in children is amoxicillin.
• Cystic fibrosis is diagnosed via newborn screening/sweat chloride test and causes recurrent infections due to CFTR gene mutations.

Related Topics

Prerequisites

• Basic respiratory anatomy and physiology (airway divisions, mechanics of breathing)
• Normal ranges for pediatric vital signs by age

Related Topics

• Upper vs. lower respiratory tract infections
• Pediatric immunization schedule (Hib, pneumococcal, RSV prophylaxis)
• Pediatric emergency assessment (ABCDE approach)

Next Topics

• Pediatric cardiovascular disorders
• Pediatric infectious diseases
• Neonatal respiratory distress syndrome