5.2 Lower Airway Infections: Bronchiolitis (RSV) & Pediatric Pneumonia

Lower Airway Infections: Bronchiolitis (RSV) & Pediatric Pneumonia

Quick Overview: Lower respiratory tract infections represent the leading cause of hospitalization in infants and young children worldwide. Bronchiolitis, predominantly driven by respiratory syncytial virus (RSV), involves acute inflammatory obstruction of the terminal and respiratory bronchioles, where supportive nursing care remains the evidence-based cornerstone of therapy. Pediatric pneumonia, spanning viral, typical bacterial (Streptococcus pneumoniae), and atypical bacterial (Mycoplasma pneumoniae) etiologies, requires age-stratified clinical assessment, targeted antimicrobial therapy, and vigilant monitoring for suppurative pleural complications such as empyema.

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1. Bronchiolitis & Respiratory Syncytial Virus (RSV): Pathophysiology & Epidemiology

Bronchiolitis is an acute viral infection of the lower respiratory tract characterized by acute inflammation, edema, and cellular necrosis of the epithelial cells lining the small conducting airways (bronchioles), accompanied by excessive mucus hypersecretion.

Viral Etiology & Epidemiology

• Primary Pathogen: Respiratory Syncytial Virus (RSV), an enveloped RNA virus of the Pneumoviridae family, is responsible for 75% to 80% of all infant bronchiolitis cases. Other significant causative viruses include human rhinovirus, human metapneumovirus (hMPV), parainfluenza virus type 3, adenoviruses, and influenza viruses. Dual viral co-infections occur in up to 30% of hospitalized infants.
• Seasonal Epidemiology: In temperate climates, RSV exhibits a predictable seasonal pattern, beginning in late autumn (October/November), peaking during mid-winter (January/February), and waning in early spring (April/May).
• Vulnerable Age Group: Peak hospitalization rates occur in infants between 2 and 6 months of age. Nearly 70% of all infants are infected during their first year of life, and virtually 100% of children have been infected at least once by age 2.

Cellular Pathophysiology & Ball-Valve Mechanics

1. Epithelial Invasion: RSV targets and infects the ciliated epithelial cells lining the nasopharynx and spreads cell-to-cell along the bronchial tree via syncytia formation (multinucleated giant cells created by the viral F-glycoprotein).
2. Inflammatory Infiltration & Necrosis: Viral replication induces extensive cellular necrosis, cilia denudation, and recruitment of inflammatory mediators (neutrophils, lymphocytes, cytokines). Submucosal peribronchial lymphocytic infiltration and interstitial edema ensue.
3. Luminal Occlusion: Sloughed necrotic epithelial cells, dense cellular debris, and hyperviscous mucus coalesce within the delicate lumina of the terminal bronchioles, causing partial or complete airway occlusion.
4. The "Ball-Valve" Mechanism: During inspiration, negative intrathoracic pressure and outward thoracic expansion pull the bronchiolar lumina open, allowing air to bypass the partial mucus obstruction. During exhalation, positive intrathoracic pressure and physiological bronchial narrowing cause the luminal debris to act as a one-way check-valve. Trapped air cannot escape, leading to alveolar hyperinflation, increased functional residual capacity, and air trapping distally. In segments where obstruction is complete, trapped distal air is absorbed into the bloodstream, producing subsegmental atelectasis.
5. V/Q Mismatch & Hypoxemia: Widespread patchy areas of hyperinflation alternating with atelectasis create marked ventilation-perfusion (V/Q) mismatch, leading to arterial hypoxemia, hypercapnia, and compensatory tachypnea.

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2. Clinical Manifestations & Staging of Bronchiolitis

Bronchiolitis characteristically exhibits a biphasic clinical progression spanning 7 to 14 days, with clinical symptoms typically peaking between days 3 and 5 of the illness:

Phase 1: Upper Respiratory Prodrome (Days 1 to 3)

• Clear, copious rhinorrhea and nasal congestion.
• Sneezing and pharyngeal erythema.
• Low-grade fever (38°C to 38.5°C / 100.4°F to 101.3°F); high fever is uncommon in uncomplicated RSV.
• Intermittent mild dry cough and slight reduction in appetite.

Phase 2: Lower Respiratory Compromise (Days 3 to 5 - Peak Severity)

• Tachypnea: Respiratory rate exceeding age-specific thresholds (frequently 60 to 80+ breaths/min).
• Auscultatory Findings: Diffuse high-pitched expiratory wheezing, coarse and fine crackles (rales) heard throughout all lung fields, and a prominently prolonged expiratory phase.
• Increased Work of Breathing: Prominent intercostal, subcostal, and suprasternal retractions, nasal flaring, and head bobbing (in infants, utilizing the sternocleidomastoid and neck extensors to maintain ventilation).
• Expiratory Grunting: A compensatory physiologic mechanism wherein the infant partially closes the glottis during expiration to generate intrinsic positive end-expiratory pressure (PEEP), preventing alveolar collapse and maintaining functional residual capacity.
• Feeding Intolerance: Inability to suckle and swallow due to tachypnea and nasal occlusion, leading to dehydration.

Central Apnea in High-Risk Infants

Apnea—defined as the cessation of breathing for 20 seconds or longer, or a shorter pause accompanied by bradycardia (HR < 80 bpm) or oxygen desaturation (SpO2 < 85%)—is a severe and potentially fatal manifestation of RSV. It occurs in up to 10% to 20% of hospitalized infants. Notably, apnea may be the presenting symptom of RSV before the development of cough or wheezing. The risk of apnea is greatest in:

• Infants younger than 2 months of age (especially neonates).
• Former premature infants (gestational age < 37 weeks).
• Infants with low birth weight (< 2,500 grams).
• Infants with underlying neuromuscular disease or central hypoventilation.

Pediatric Respiratory Distress Scoring & Vital Sign Thresholds

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3. AAP Clinical Practice Guidelines: Evidence-Based Management & De-Implementation

The American Academy of Pediatrics (AAP) Clinical Practice Guideline on Bronchiolitis emphasizes that supportive care is the foundation of management. A critical component of PED-BC examination competency is understanding what NOT to do (de-implementation of ineffective and potentially harmful interventions):

Core Supportive Nursing Interventions (What TO Do)

1. Airway Clearance via Nasal Suctioning: Infants are obligate nasal breathers. Thorough superficial suctioning of the anterior nares using a bulb syringe, Neosucker, or olive-tip aspirator immediately prior to feedings and before sleep relieves upper airway resistance and improves tidal volume. Avoid deep, aggressive catheter suctioning of the nasopharynx, which induces mucosal edema, trauma, and reflex bradycardia.
2. Hydration & Nutritional Support: Tachypneic infants exhibit increased insensible fluid loss and poor oral intake. If the respiratory rate is >60 to 70 breaths/min, oral feeding (bottle or breast) is contraindicated due to the high risk of aspiration and diaphragmatic fatigue. Administer isotonic intravenous fluids (such as D5 0.9% NS or D5 0.45% NS with 20 mEq/L KCl) at maintenance rates, or provide slow continuous enteral feeds via a nasogastric (NG) tube.
3. Judicious Humidified Oxygen Therapy: Administer supplemental humidified oxygen only when the child's oxygen saturation drops persistently below 90% (or <92% in infants with high-risk underlying cardiopulmonary disease). Discontinue supplemental oxygen when SpO2 >= 90% on room air with adequate clinical improvement. Routine use of continuous pulse oximetry is discouraged in clinically stable infants once oxygen is discontinued, as it prolongs hospitalization without improving outcomes.
4. Heated Humidified High-Flow Nasal Cannula (HFNC): In infants exhibiting moderate-to-severe respiratory distress, HFNC delivers heated, fully humidified oxygen/air mixtures at flow rates of 1 to 2 L/kg/min. HFNC generates a modest amount of positive airway pressure (PEEP), flushes anatomical nasopharyngeal dead space, decreases the work of breathing, and reduces the need for endotracheal intubation.

The AAP "Do NOT Do" Recommendations (De-Implementation Rules)

+-------------------------------------------------------------------------+
|          AAP EVIDENCE-BASED GUIDELINES: PRACTICES TO AVOID             |
+-------------------------------------------------------------------------+
|  1. NO ROUTINE BRONCHODILATORS (Albuterol / Levalbuterol):             |
|     Large randomized clinical trials demonstrate that albuterol does    |
|     not improve oxygenation, reduce hospital admission rates, or        |
|     shorten hospital length of stay in bronchiolitis. Adverse effects   |
|     include tachycardia, tremor, and hypokalemia.                       |
|                                                                         |
|  2. NO SYSTEMIC CORTICOSTEROIDS (Dexamethasone / Prednisolone):        |
|     Steroids do not reduce viral replication, improve clinical scores,   |
|     or prevent hospitalization in viral bronchiolitis.                  |
|                                                                         |
|  3. NO ROUTINE ANTIBIOTICS:                                             |
|     Bronchiolitis is viral. The rate of secondary bacterial pneumonia   |
|     in infants with RSV is < 1%. Inappropriate antibiotic use promotes |
|     microbial resistance and Clostridioides difficile colitis.          |
|                                                                         |
|  4. NO ROUTINE CHEST RADIOGRAPHY:                                       |
|     Chest X-rays in bronchiolitis frequently show patchy subsegmental    |
|     atelectasis that mimics bacterial consolidation, leading to         |
|     inappropriate antibiotic prescriptions.                             |
|                                                                         |
|  5. NO ROUTINE CHEST PHYSIOTHERAPY (CPT):                               |
|     Manual percussion and postural drainage do not open obstructed       |
|     bronchioles and cause unnecessary infant agitation and fatigue.     |
+-------------------------------------------------------------------------+

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4. Immunoprophylaxis for High-Risk Populations

Because no effective therapeutic antiviral agent exists for active RSV bronchiolitis, clinical efforts focus on passive immunoprophylaxis for infants at the highest risk for severe morbidity and mortality.

Current infant RSV prevention

CDC recommends protection through maternal RSV vaccination or an infant long-acting monoclonal antibody, usually not both. Nirsevimab or clesrovimab may be used for eligible infants younger than 8 months entering their first season when maternal vaccination did not provide protection. Verify maternal vaccination status and timing, age, product eligibility, season, and the current order. Nirsevimab also has recommendations for selected high-risk children aged 8–19 months entering a second season; clesrovimab is not the second-season product. Palivizumab is no longer available after December 31, 2025, so a 2026 plan must not prescribe its former monthly regimen as the default. These antibodies prevent severe illness; they do not treat established bronchiolitis.

CDC infant RSV guidance, checked October 18, 2026

Nirsevimab (Beyfortus)

• Mechanism & Utilization: Nirsevimab is a long-acting recombinant monoclonal antibody with an engineered triple amino acid substitution (YTE) in the Fc region that extends its serum half-life to approximately 60 to 70 days. A single intramuscular injection provides sustained protective antibody titers for at least 5 months (spanning an entire RSV season).
• Indications: Recommended for all infants younger than 8 months of age born during or entering their first RSV season (50 mg IM for weight < 5 kg; 100 mg IM for weight >= 5 kg), as well as high-risk children aged 8 to 19 months entering their second season (200 mg IM).

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5. Pediatric Community-Acquired Pneumonia (CAP)

Pediatric community-acquired pneumonia (CAP) is an acute infection of the pulmonary parenchymal tissue (alveoli and interstitium) acquired outside of a healthcare facility.

Age-Stratified Microbial Etiologies

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|                PEDIATRIC PNEUMONIA ETIOLOGY BY AGE                      |
+-------------------------------------------------------------------------+
|  NEONATES (< 28 DAYS):                                                  |
|  - Group B Streptococcus (GBS - Streptococcus agalactiae)               |
|  - Escherichia coli & Gram-negative enteric bacilli                     |
|  - Listeria monocytogenes                                               |
+-------------------------------------------------------------------------+
|  INFANTS & TODDLERS (1 MONTH TO 5 YEARS):                               |
|  - Viruses (> 50-70%): RSV, Human Metapneumovirus, Parainfluenza, Adeno |
|  - Bacterial: Streptococcus pneumoniae (most common bacterial cause)    |
|  - Other Bacterial: Staphylococcus aureus, non-typeable H. influenzae   |
+-------------------------------------------------------------------------+
|  SCHOOL-AGE CHILDREN & ADOLESCENTS (> 5 YEARS):                         |
|  - Atypical Bacteria: Mycoplasma pneumoniae, Chlamydophila pneumoniae   |
|  - Typical Bacteria: Streptococcus pneumoniae                           |
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Clinical Manifestations: Typical Bacterial vs. Atypical vs. Viral

• Tachypnea: The single most sensitive and specific clinical indicator of pediatric pneumonia recognized by the World Health Organization (WHO).
  • WHO Age-Specific Tachypnea Cutoffs:
    • Age < 2 months: >= 60 breaths/min
    • Age 2 to 11 months: >= 50 breaths/min
    • Age 1 to 5 years: >= 40 breaths/min
    • Age > 5 years: >= 20 to 30 breaths/min
• Typical Bacterial Pneumonia (Streptococcus pneumoniae): Characterized by acute, abrupt onset of high fever (>39°C), chills, productive cough, tachypnea, and chest pain. Auscultation reveals localized focal tubular (bronchial) breath sounds, crackles, and increased tactile fremitus over the consolidated lobe.
• Referred Abdominal Pain: Lower lobe pneumonia (especially right lower lobe) commonly irritates the diaphragmatic pleura, sending pain impulses along the 7th through 11th intercostal nerves. Young children present with localized right lower quadrant abdominal pain, vomiting, and abdominal guarding, closely mimicking acute appendicitis.
• Atypical "Walking" Pneumonia (Mycoplasma pneumoniae): Characterized by an insidious onset in school-age children and adolescents. Symptoms include headache, malaise, low-grade fever, sore throat, and a persistent, dry, intractable, paroxysmal hacking cough. Auscultation reveals diffuse bilateral fine rales or wheezing rather than focal consolidation. Extrapulmonary manifestations include erythema multiforme rashes and autoimmune hemolytic anemia.

Diagnostic Radiography & Laboratory Workup

• Chest Radiography: Posterior-anterior (PA) and lateral views differentiate lobar consolidation (typical bacterial pneumonia) from diffuse bilateral perihilar streaky or interstitial infiltrates (viral or atypical pneumonia). Imaging is essential to identify complications (pleural effusion, lung abscess, pneumatocele).
• Blood Cultures: Indicated for children requiring hospitalization with moderate-to-severe pneumonia or failed outpatient therapy. Sputum cultures are rarely obtainable in young children who swallow secretions.

Evidence-Based Antimicrobial Protocols

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6. Complications: Parapneumonic Effusion & Empyema

A parapneumonic effusion is the accumulation of fluid in the pleural space secondary to adjacent parenchymal pneumonia. When the pleural fluid becomes infected and purulent with fibrin deposition and loculations, it is termed an empyema.

Clinical Red Flags for Empyema

• Persistent High Fever: The child continues to spike high fevers despite 48 to 72 hours of compliant intravenous antibiotic therapy.
• Unilateral Absent Breath Sounds: Auscultation reveals a complete absence of breath sounds over the affected hemithorax.
• Stony Dullness: Percussion of the chest wall reveals profound "stony" dullness over the lower lung fields.
• Tracheal & Mediastinal Shift: A large, tense tension-effusion pushes the trachea and heart to the contralateral side.

Pleural Fluid Diagnostic Biomarkers

Thoracentesis reveals definitive biochemical criteria differentiating simple exudative effusion from complicated empyema:

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|               DIAGNOSTIC CRITERIA FOR PEDIATRIC EMPYEMA                 |
+-------------------------------------------------------------------------+
|  - Appearance: Purulent, thick, cloudy exudative fluid                  |
|  - Pleural Fluid pH: < 7.20 (acidic due to anaerobic bacterial metabolism)|
|  - Pleural Fluid Glucose: < 40 mg/dL (consumed by active bacteria)      |
|  - Pleural Fluid LDH: > 1,000 U/L (severe cellular lysis and inflammation)|
|  - Pleural WBC: Markedly elevated (> 50,000/mcL) with neutrophil dominance|
|  - Positive Gram stain and culture (commonly S. pneumoniae or S. aureus)|
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Management of Empyema

1. Chest Tube Thoracostomy: Placement of a pigtail catheter or chest tube attached to water-seal suction (-10 to -20 cm H2O) to evacuate purulent fluid and re-expand the lung.
2. Intrapleural Fibrinolytic Instillation: To dissolve dense fibrin septations and loculations without open surgery, tissue plasminogen activator (tPA / alteplase) and dornase alfa are instilled via the chest tube and allowed to dwell for 1 to 2 hours before unclamping to suction.
3. Video-Assisted Thoracoscopic Surgery (VATS): Indicated for organized, multi-loculated empyemas refractory to fibrinolysis to perform mechanical debridement, decortication, and break down thick fibrous adhesions.