A 3-year-old child presents to the emergency department with acute onset of coughing and stridor after playing with peanuts. On examination, there is unilateral decreased air entry on the right side with hyperinflation of the right hemithorax. Which investigation is most appropriate to confirm the diagnosis and localize the foreign body?

## Investigation of Choice for Suspected Foreign Body Airway ### Clinical Presentation Analysis The child presents with classic features of foreign body aspiration: - Acute onset coughing after aspiration risk event - Unilateral decreased air entry (right side) - Hyperinflation of right hemithorax (air trapping distal to obstruction) ### Why Chest X-ray (Inspiratory and Expiratory Views) is Correct **Key Point:** Inspiratory and expiratory chest X-rays are the gold standard initial investigation for suspected foreign body airway in pediatric patients. **High-Yield:** The expiratory view is diagnostic because: 1. During expiration, air is normally expelled from both lungs 2. If a foreign body obstructs the right main bronchus, air becomes trapped distal to the obstruction 3. The right hemithorax remains hyperinflated (hyperlucent) on expiratory view while the left lung collapses normally 4. This **unilateral hyperinflation** on expiratory view is pathognomonic for foreign body aspiration **Clinical Pearl:** In young children who cannot cooperate for expiratory films, a decubitus view (child lying on the affected side) can be used instead — the dependent lung should collapse normally, while the affected side remains hyperinflated. ### Diagnostic Accuracy | Finding | Inspiratory View | Expiratory View | Clinical Significance | |---------|------------------|-----------------|----------------------| | Normal lung | Aerated bilaterally | Collapses symmetrically | No obstruction | | Foreign body | May show radiopaque object | Unilateral hyperinflation (affected side) | Diagnostic for FB | | Air trapping | Subtle hyperinflation | Marked unilateral hyperlucency | Confirms obstruction | **Mnemonic:** **EXPIRATORY VIEW = EVIDENCE** — The expiratory view provides the diagnostic evidence by demonstrating persistent hyperinflation on the affected side. ### Role of Rigid Bronchoscopy Rigid bronchoscopy is the **definitive therapeutic intervention**, not a diagnostic test. It is performed AFTER X-ray confirmation and is used to visualize and remove the foreign body under direct visualization with airway protection.