A 35-year-old woman is admitted with extensive thermal injuries from a house fire. The treating team suspects inhalation injury given her singed nasal hairs and carbonaceous sputum. Which investigation is most appropriate to confirm the diagnosis of inhalation injury and assess severity?

## Investigation of Choice for Inhalation Injury Diagnosis ### Fiberoptic Bronchoscopy: Gold Standard **Key Point:** Fiberoptic bronchoscopy with direct visualization of the airway is the gold standard and most specific investigation for diagnosing inhalation injury, allowing direct assessment of airway damage, soot deposition, and mucosal injury. **High-Yield:** Bronchoscopy findings in inhalation injury include: - Carbonaceous deposits in airways - Mucosal erythema and edema - Blistering and ulceration of respiratory mucosa - Airway obstruction from swelling - Severity grading (Abbreviated Injury Scale) ### Diagnostic Approach to Inhalation Injury ```mermaid flowchart TD A[Suspected inhalation injury]:::outcome --> B{Clinical signs present?}:::decision B -->|Singed nasal hairs, carbonaceous sputum, stridor| C[Perform fiberoptic bronchoscopy]:::action C --> D{Direct visualization findings?}:::decision D -->|Carbonaceous deposits, mucosal injury| E[Confirmed inhalation injury]:::outcome D -->|Normal airways| F[Inhalation injury excluded]:::outcome B -->|Equivocal signs| G[Supportive tests: ABG, CXR, COHb]:::action G --> H[Bronchoscopy if still suspected]:::action ``` ### Comparison of Investigations | Investigation | Sensitivity | Specificity | Timing | Role | |---|---|---|---|---| | Fiberoptic Bronchoscopy | 95–100% | 100% | Early (within 24 hrs) | **Gold standard; direct diagnosis** | | Arterial Blood Gas | Moderate | Low | Early | Detects hypoxemia, acidosis (non-specific) | | Carboxyhemoglobin (COHb) | 80% | Moderate | Early | Confirms CO exposure; not specific for airway injury | | Chest X-ray | 30–40% | Moderate | Early | Late findings; may be initially normal | | Pulmonary Function Tests | Moderate | Low | Late | Functional assessment; not diagnostic | **Clinical Pearl:** Chest X-ray is often normal in the first 24–48 hours despite severe inhalation injury. Bronchoscopy is therefore essential for early diagnosis and severity grading, which guides airway management and prognosis. **Mnemonic:** **SCOPE** = **S**oot **C**arbon **O**bservation **P**rovides **E**arly diagnosis — fiberoptic bronchoscopy allows direct visualization of inhalation injury. ### Clinical Application in This Case The patient has clinical red flags for inhalation injury: - Singed nasal hairs (indicates high-temperature exposure to upper airway) - Carbonaceous sputum (evidence of soot in lower airway) **Fiberoptic bronchoscopy would:** 1. Confirm inhalation injury by direct visualization of carbonaceous deposits and mucosal damage 2. Grade severity (mild, moderate, severe) using standardized criteria 3. Guide intubation decisions and airway management 4. Assess need for aggressive pulmonary toilet and ventilatory support 5. Provide prognostic information (severe inhalation injury increases mortality)