From the Guidelines
For a COPD exacerbation, a chest X-ray (CXR) is the primary imaging study recommended. This should be ordered as a standard posteroanterior and lateral view to evaluate for potential complications or alternative diagnoses that might be causing or contributing to the exacerbation. The chest X-ray can help identify pneumonia, pneumothorax, pleural effusion, pulmonary edema, or other acute processes that may mimic or complicate COPD exacerbation. According to the American College of Radiology Appropriateness Criteria 1, a chest radiograph is usually appropriate for the initial imaging of complicated acute COPD exacerbation in immunocompetent patients.
Key Points to Consider
- The chest X-ray is useful in identifying complications such as pneumonia or pneumothorax, as noted in the European Respiratory Society task force report 1.
- Advanced imaging such as CT scans is not routinely needed for uncomplicated COPD exacerbations, as suggested by the management of acute exacerbations of chronic obstructive pulmonary disease review 1.
- However, if the clinical presentation is atypical, if there is poor response to standard therapy, or if complications are suspected (such as pulmonary embolism), a CT scan of the chest may be warranted.
- For suspected pulmonary embolism specifically, a CT pulmonary angiogram (CTPA) would be the appropriate study.
Rationale
The rationale for limiting imaging to chest X-ray in most cases is to minimize radiation exposure while still obtaining clinically useful information that can guide management decisions in the acute setting. This approach is supported by the most recent and highest quality study available, which emphasizes the importance of chest radiography in the initial assessment of COPD exacerbations 1.
From the Research
Imaging Options for COPD Exacerbation
- Computed Tomography (CT) is considered the standard modality to objectively visualize lung disease, providing useful measures of the presence and extent of emphysema, airway disease, and pulmonary vascular disease 2.
- Chest X-ray is almost universally available but lacks sensitivity in detecting both airway disease and mild emphysema, and is not generally amenable to objective analysis 2.
- Other imaging techniques such as optical coherence tomography (OCT) and magnetic resonance imaging (MRI) offer exciting in vivo insights into lung structure and function, but are limited by their availability 2.
Characteristics of COPD Exacerbation on Imaging
- An exacerbation is characterized by airway wall and airway calibre changes, hyperinflation, pulmonary vasoconstriction, and imaging features suggestive of pulmonary arterial hypertension 3.
- Consolidation visible on a chest X-ray is associated with higher mortality in COPD patients admitted to hospital due to an exacerbation 4.
Limitations and Considerations
- Pulse oximetry may overestimate oxygen saturation in COPD patients, with a mean difference (bias) between SaO2 and SpO2 of -3.98 (95% CI -4.68 to 3.28) 5.
- The performance of pulse oximetry can vary depending on the type of COPD, with less sensitivity and positive predictive value in subjects with chronic bronchitis versus emphysema 5.