Josh Sowick, PGY-1
Article: Lung Ultrasound for the Emergency Diagnosis of Pneumonia, Acute Heart Failure, and Exacerbations of Chronic Obstructive Pulmonary Disease/Asthma in Adults: A systemic review and Meta-Analysis. Staub, et al
Background: In the Emergency Department setting, Lung Ultrasound (LUS) is widely accepted as a valuable diagnostic tool in the rapid assessment of patients in respiratory distress. Many readers will be familiar with the utility of LUS for differentiation of COPD/Asthma Exacerbation from Pulmonary Edema secondary to acute decompensated heart failure, or in the diagnosis of a pneumonia. The authors of this paper systematically reviewed the available literature for prospective studies on the accuracy of the LUS for the emergency diagnosis of pneumonia, acute heart failure, and exacerbations of COPD/asthma.
Study Type: A meta-analysis of Prospective Diagnostic Accuracy Studies in the diagnosis of pneumonia, COPD/Asthma, and Heart Failure with Lung Ultrasound.
Study: Twenty-five studies were included, most of which had assessed pneumonia and acute heart failure, although some assessed all 3 diagnoses. The studies were heterogeneous in their characteristics and results, and the overall methodological quality was low, although this is not surprising in a meta-analysis with sonographers of varying levels of training, different practice settings (ED and ICU), and different lung ultrasound protocols.
Almost all of the studies were in the ED, some were in the ICU, none were in intubated patients, although some of the patients ended up being intubated later in their course. The studies had an overall moderate-high prevalence for the diseases assessed, the age was older across the board (60-80 years old), which makes sense based on the higher prevalence of these disease processes in the elderly.
The primary outcome was Number of True and False Positives, and True and False Negatives. The authors highlighted the importance of clinical judgment when the diagnosis represents a clinical event like dyspnea, therefore the final diagnosis by experts was considered as an appropriate reference standard. For pneumonia, diagnostic strategies including CXR or CT were used as an appropriate reference standard, but not CXR alone.The main inclusion criteria for studies looking for pneumonia was s/s of pneumonia (fevers/chills, productive cough, dyspnea, pleuritic chest pain). The studies assessing PNA and COPD/Asthma or Heart Failure, or all three, used Acute Dyspnea or Acute Respiratory Failure as their main inclusion criteria. The studies looking at Acute Heart Failure alone used Acute Dyspnea as main inclusion criteria.
In general, all the studies looked at anterior, lateral and posterior lung fields, however other methods included:
• Upper and lower in ant, lat, and post. regions of each hemi-thorax.
• Eight areas (not specified by the study)
• All intercostal spaces from apex to diaphragm in hemi-clavicular, anterior axillary line, mid-axillary line and para-vertebral line.
• BLUE protocol (method for LUS by Dr. Lichtenstein, with the aim of suggesting a diagnosis of COPD/Asthma, PTX, PNA, or PE/DVT with an accuracy of >90%. The method is more or less similar to the above listed methods)
Ultrasound Evaluation of LungsThere was a wide variation in the sensitivity and specificity of each ultrasound finding for each disease process, so we’ll go into each diagnosis separately to discuss the diagnostic accuracy of the most important sonographic findings you should know about.
PneumoniaSonographic consolidation was highly specific (94%) but moderately sensitive (80%) for pneumonia in patients suspected to have this disease.If you used consolidation OR focal interstitial syndrome (B-lines in focal area of lung tissue) as your diagnostic criteria, the sensitivity increased (95%) at the cost of specificity (74%). This may happen because, even while not detecting deep consolidations, LUS can detect the interstitial edema surrounding these lesions. Takeaways for LUS of Pneumonia: Consolidation is useful to confirm pneumonia, not sensitive enough to rule it out. Absence of both consolidation and focal interstitial syndrome can better rule out this disease. Either way, you’re still going to get a CXR and/or CT chest if you are suspicious for pneumonia.
Acute Heart Failure
Diffuse interstitial syndrome (B-lines bilaterally and in multiple lung fields) was a fairly accurate indicator of acute heart failure in patients with acute dyspnea according to this meta analysis (Sens 73% Spec 84%).
However the authors also cited a study where the sonographers were all experienced ED providers who had the opportunity to state each patient’s pre-test probability of Acute Heart Failure prior to lung ultrasound, after looking at an EKG, lab work including blood gas, past medical history, HPI, and exam. The authors of that study called this ‘Modified Diffuse Interstitial Syndrome’, I prefer to call it ‘realistic’. In this case, there was a significant improvement of this LUS finding in the diagnosis of acute heart failure: Sens was 90% and Spec was 93%.
Takeaways for LUS of Acute Heart Failure: It’s Important to consider the presence of other diseases that follow this course and can produce diffuse B-lines bilaterally, such as interstitial pneumonia, ARDS, lung fibrosis, which can compromise the accuracy of these findings for diagnosing acute heart failure (this is part of why the test does better when you have more information and a refined clinical gestalt).
COPD/Asthma Exacerbation
Without overlapping parenchymal diseases, exacerbations of COPD or asthma do not coincide with a significant loss of lung parenchyma aeration or pleural effusions. A-lines in all lung fields without abnormal findings suggestive of the other above diagnoses (no B-lines, no consolidations, no pleural effusions) is the sonographic pattern for these diseases; Sens 70-80%, Spec 90-98%
Takeaways for LUS of COPD/Asthma: If a patient presents in acute dyspnea, an experienced ED provider is suspicious for the diagnosis of COPD/Asthma Exacerbation, and the patient’s lung ultrasound doesn’t look consistent with any of the pathologic lung ultrasound profiles, the diagnosis is more likely to be COPD or asthma exacerbation.