Can a computed tomography pulmonary embolism (CT PE) scan adequately reassess left lobe consolidation in a patient with suspected chronic obstructive pulmonary disease (COPD) exacerbation and hypoxia?

From the Guidelines

A CT pulmonary embolism (CT PE) study can adequately reassess the previously noted left lobe consolidation in a patient with suspected chronic obstructive pulmonary disease (COPD) exacerbation and hypoxia, as it provides detailed visualization of lung parenchyma and can help distinguish between vascular structures and solid masses 1.

Key Considerations

• The patient's current symptoms of hypoxia and tachycardia could be related to either a pulmonary embolism or progression of the lung consolidation, making a comprehensive study like CT PE crucial for timely clinical information.
• CT PE protocols typically include high-resolution imaging of the entire chest, which can provide sufficient detail to assess whether the previously noted consolidation has resolved, progressed, or remained stable.
• The contrast enhancement used in CT PE studies offers an advantage in evaluating lung lesions, as it can help distinguish between vascular structures and solid masses, and may provide information about lesion enhancement patterns.

Clinical Context

• In patients with COPD, it is essential to carefully monitor for hypercapnic respiratory failure with respiratory acidosis, which may develop during a hospital admission, even if initial blood gases were satisfactory 1.
• Avoiding excessive oxygen use in patients with COPD is crucial, as it can increase the risk of respiratory acidosis in patients with hypercapnic respiratory failure.

Imaging Considerations

• While a standard chest CT might use different timing for contrast administration and slightly different technical parameters, a CT PE study will still provide sufficient detail to assess lung parenchyma and lesions.
• Using one comprehensive study like CT PE instead of ordering separate scans reduces radiation exposure and provides timely clinical information to guide management of acutely ill patients.

Recommendation

• In this clinical scenario, a CT PE study is a reasonable choice for reassessing left lobe consolidation in a patient with suspected COPD exacerbation and hypoxia, considering its ability to provide detailed visualization of lung parenchyma and distinguish between vascular structures and solid masses 1.

From the Research

Computed Tomography Pulmonary Embolism (CT PE) Scan in COPD Exacerbation

• A CT PE scan can be used to diagnose pulmonary embolism (PE) in patients with suspected chronic obstructive pulmonary disease (COPD) exacerbation and hypoxia 2, 3, 4.
• The scan can provide both structural and functional information, including the quantification of tissue perfusion, which may yield more important information for patient management than the direct visualization of emboli by CT alone 3.
• However, the optimal diagnostic strategy for PE in patients with COPD exacerbation remains undetermined, and further studies are needed to improve diagnostic management in this population 5.

Left Lobe Consolidation Reassessment

• A normal computed tomography pulmonary angiography (CTPA) can be considered a valid diagnostic criterion to rule out PE in the majority of patients with a likely clinical probability, although the risk of venous thromboembolism (VTE) is higher in subgroups such as patients with a Wells rule >6 points 6.
• There is no direct evidence to suggest that a CT PE scan can adequately reassess left lobe consolidation in a patient with suspected COPD exacerbation and hypoxia.
• The use of clinical decision tools, such as the revised Geneva and Wells PE scores combined with fixed D-dimer cut-off, can help reduce the need for imaging, but may increase the VTE diagnosis failure rate 5.

Diagnostic Strategies

• The revised Geneva and Wells PE scores combined with fixed D-dimer cut-off had a diagnostic failure rate of VTE of 0.7% (95%CI 0.3%-1.7%), but >70.0% of the patients needed imaging 5.
• CTPA-sparing diagnostic algorithms can reduce the need for CTPAs, but may increase the VTE diagnosis failure rate 5.
• Further studies are needed to determine the optimal diagnostic strategy for PE in patients with COPD exacerbation and to improve diagnostic management in this population 5.