5.1 Acute Pediatric Respiratory Infections

Acute Pediatric Respiratory Infections in Clinical Practice

Pediatric respiratory infections are among the most common presentations in emergency departments and primary care clinics. Due to distinct anatomical differences in children—such as a narrower airway lumen, a more compliant chest wall, a larger tongue relative to the oral cavity, and fewer collateral ventilatory channels—mild mucosal inflammation can cause disproportionately severe airway obstruction. According to Poiseuille's Law, resistance to airflow is inversely proportional to the fourth power of the airway radius (R is proportional to 1/r^4). In an infant, 1 mm of circumferential mucosal edema reduces the cross-sectional airway area by over 50% and increases airway resistance sixteen-fold. Consequently, rapid clinical assessment, accurate diagnosis, and prompt initiation of evidence-based interventions are vital.

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Croup (Laryngotracheobronchitis)

Croup is a viral infection of the upper airway that causes inflammation and edema of the subglottic larynx and trachea. It primarily affects children aged 6 months to 3 years, peaking during late autumn and early winter.

Etiology and Pathophysiology

The primary causative agent is Parainfluenza virus type 1 (responsible for up to 60% of cases), followed by Parainfluenza types 2 and 3, Respiratory Syncytial Virus (RSV), influenza viruses, and adenovirus. Viral infiltration leads to mucosal inflammation, hyperemia, and edema of the subglottic space. The rigid cricoid cartilage prevents outward expansion of the tissue, resulting in significant narrowing of the subglottic airway lumen.

Clinical Presentation

Croup typically begins with a 1-to-3-day prodrome of coryza, congestion, and low-grade fever. This progresses to:

• A harsh, metallic, barking cough (often compared to a seal's bark)
• Inspiratory stridor (a high-pitched monophonic sound produced by turbulent airflow through the narrowed subglottic space)
• Hoarseness due to vocal cord inflammation
• Retractions (subcostal, intercostal, and suprasternal) and nasal flaring, indicating increased work of breathing Symptoms typically worsen at night and when the child is agitated.

Severity Assessment: The Westley Croup Score

The Westley Croup Score is the clinical standard for grading croup severity. It evaluates five parameters:

1. Inspiratory Stridor: None (0), with agitation (1), at rest (2)
2. Retractions: None (0), mild (1), moderate (2), severe (3)
3. Air Entry: Normal (0), decreased (1), severely decreased (2)
4. Cyanosis: None (0), with agitation (4), at rest (5)
5. Level of Consciousness: Normal (0), disoriented/altered (5)

• Mild Croup (Score <= 2): Barking cough, no stridor at rest, no or minimal retractions.
• Moderate Croup (Score 3–7): Stridor at rest, moderate retractions, mild agitation.
• Severe Croup (Score >= 8): Prominent stridor at rest, marked retractions, significant agitation, or lethargy suggesting impending respiratory failure.

Pharmacotherapy and Clinical Protocols

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Bronchiolitis

Bronchiolitis is an acute inflammatory injury of the bronchioles, representing the most common lower respiratory tract infection in infants under 12 months of age.

Etiology and Epidemiology

Respiratory Syncytial Virus (RSV) is the pathogen in 70–80% of cases, peaking in winter. Other etiologies include rhinovirus, human metapneumovirus, and influenza. Risk factors for severe disease include prematurity (<35 weeks gestation), age under 12 weeks, chronic lung disease of prematurity, congenital heart disease, and immunodeficiency.

Pathophysiology

Viral replication in epithelial cells leads to necrosis, ciliary destruction, and intense lymphocytic infiltration. This results in edema of the bronchiolar walls, mucus plugging, and sloughing of necrotic cells into the narrow airway lumen. The obstruction causes mismatched ventilation-perfusion, air trapping (hyperinflation), and atelectasis.

Clinical Presentation and Progression

1. Prodrome (Days 1–3): Clear rhinorrhea, sneezing, and low-grade fever.
2. Lower Respiratory Phase (Days 4–6): Tachypnea, hacking cough, diffuse expiratory wheezes, fine crackles, accessory muscle use (subcostal/intercostal retractions, nasal flaring), and poor feeding.
3. Resolution (Days 7–14): Gradual improvement, though cough can persist for 3 weeks.

Evidence-Based Supportive Care (AAP Guidelines)

Clinical practice guidelines from the American Academy of Pediatrics (AAP) emphasize that bronchiolitis is a self-limiting disease managed primarily with supportive care:

• Nasal Suctioning: Superficial suctioning of the nares with a bulb syringe or suction catheter before feeding and sleeping to clear mucous obstruction. Avoid deep nasopharyngeal suctioning as it increases mucosal edema.
• Hydration: Monitor fluid intake and output. If the respiratory rate exceeds 60 breaths per minute, oral feeding is contraindicated due to the high risk of microaspiration. In such cases, administer fluids via nasogastric tube or intravenous lines.
• Oxygen Therapy: Supplemental oxygen is indicated only if oxygen saturation (SpO2) drops below 90% in healthy infants. Use high-flow nasal cannula (HFNC) if respiratory distress escalates.

[!IMPORTANT] Interventions NOT Recommended: The AAP guidelines strongly advise against the routine use of: albuterol/salbutamol, nebulized epinephrine, systemic or inhaled corticosteroids (e.g., dexamethasone, prednisolone), chest physiotherapy, or routine antibiotics (unless a secondary bacterial infection like acute otitis media is confirmed).

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Epiglottitis (Supraglottitis)

Epiglottitis is a rapidly progressive, life-threatening bacterial infection of the epiglottis and surrounding supraglottic structures that can cause sudden, complete airway obstruction.

Etiology and Epidemiology

Historically, Haemophilus influenzae type B (Hib) was the primary cause. Following the widespread introduction of the Hib conjugate vaccine, incidence has plummeted. Current cases are rare and usually occur in unvaccinated children, under-vaccinated individuals, or are caused by other pathogens such as Streptococcus pyogenes, Streptococcus pneumoniae, and Staphylococcus aureus.

Clinical Presentation and the "4 Ds"

Epiglottitis has a rapid, fulminant onset over hours. The child appears toxic, anxious, and septic, with a high fever (often >39.0°C). The classic clinical picture is dominated by the "4 Ds":

1. Drooling: The child cannot swallow saliva due to severe supraglottic pain (odynophagia).
2. Dysphagia: Intense pain on attempts to swallow.
3. Dysphonia: Muffled, soft speech (referred to as a "hot potato voice").
4. Distressed Inspiratory Efforts: Audible inspiratory stridor and severe retractions.

To maximize the airway diameter mechanically, the child will spontaneously adopt the tripod position (sitting upright, leaning forward, resting hands on knees, neck hyperextended, jaw thrust forward) or the sniffing position.

Emergency Airway Protocol

If epiglottitis is suspected, the clinician must follow a strict, non-negotiable airway safety protocol:

• Do NOT Inspect the Throat: Never attempt to visualize the pharynx, insert a tongue depressor, or obtain a throat culture in a non-controlled setting. Mechanical stimulation of the swollen epiglottis can trigger immediate, complete laryngospasm and total airway closure.
• Keep the Child Calm: Allow the child to remain in the parent's lap. Avoid painful procedures, intravenous cannulation, or laboratory draws that cause crying. Crying increases negative intrapleural pressure, accelerating airway collapse.
• Mobilize the Emergency Airway Team: Immediately call a senior pediatric anesthesiologist, an otolaryngologist (ENT surgeon), and a pediatric intensivist.
• Controlled Airway Management: Transport the child directly to the operating room (OR). The ENT surgeon must be present in the OR with sterile tracheostomy instruments open and ready. Anesthesia is induced using inhalational agents (e.g., sevoflurane) in the upright position. Once deep anesthesia is achieved, controlled endotracheal intubation is performed. Intubation is typically maintained for 24–48 hours until supraglottic swelling decreases, as confirmed by direct visualization under anesthesia.
• Post-Airway Stabilisation: After the airway is secured, obtain blood cultures and initiate intravenous antibiotics (e.g., a third-generation cephalosporin such as Ceftriaxone, combined with Vancomycin if MRSA is suspected).