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Difficulty: MediumPediatric Respiratory Disorders

Concerned parents bring their 5-month-old son to the acute care clinic in mid-December. They report that for the past 24 hours, the infant has been breathing very rapidly and refusing his formula. His symptoms began 3 days earlier with clear rhinorrhea and a tactile fever. His medical history includes delivery at 31 weeks of gestation. Current vital signs indicate a temperature of 38.1°C (100.6°F), heart rate of 158/min, and respiratory rate of 70/min. Pulse oximetry demonstrates an oxygen saturation of 88% while breathing room air. On examination, the infant exhibits grunting, severe subcostal retractions, and widespread expiratory wheezing mixed with fine crackles on auscultation. Which of the following best describes the predominant underlying mechanism responsible for this patient's respiratory distress?

  1. Epithelial necrosis and sloughing of the small airwaysAnswer
  2. B
    Bronchial smooth muscle hypertrophy and eosinophilic infiltration
  3. C
    Bacterial proliferation and consolidation of the alveolar spaces
  4. D
    Increased pulmonary capillary hydrostatic pressure and alveolar transudation
  5. E
    Mucosal inflammation and edema of the subglottic trachea

Answer

Epithelial necrosis and sloughing of the small airways
The correct answer is epithelial necrosis and sloughing of the small airways. The clinical presentation of a viral prodrome followed by tachypnea, severe retractions, wheezing, and fine crackles in a 5-month-old during winter is classic for acute bronchiolitis. The most common etiology is Respiratory Syncytial Virus (RSV). The virus infects the lower respiratory tract, leading to widespread necrosis of the bronchiolar epithelium. The combination of sloughed epithelial cells, inflammatory edema, and increased mucus production causes mechanical small airway obstruction, air trapping, and the resulting clinical signs.

Step-by-Step Solution

1
Analyze the patient's age, onset of symptoms, and history.
A 5-month-old infant with a 3-day viral prodrome (rhinorrhea, fever) progressing to severe lower respiratory distress.
This pattern strongly points to a viral lower respiratory tract infection, most likely acute bronchiolitis, which peaks in incidence during the winter months.
2
Evaluate the physical examination findings.
Tachypnea, severe retractions, diffuse expiratory wheezing, and fine crackles.
These signs confirm diffuse small airway obstruction, which is typical of bronchiolitis and distinguishes it from upper airway diseases like croup.
3
Identify the pathophysiologic mechanism for the suspected diagnosis.
Respiratory Syncytial Virus (RSV) infection causes necrosis of the bronchiolar epithelium.
The combination of sloughed necrotic epithelial cells, inflammatory edema, and increased mucus production creates plugs that physically obstruct the small airways.

Key Concept

Acute bronchiolitis in infants is primarily caused by RSV infection, which leads to small airway obstruction via necrosis and sloughing of the respiratory epithelium, inflammatory edema, and mucus plugging.
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Topics

Pediatric Respiratory Disorders

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