Positive zone for B-lines: A positive zone is determined when there are at least 3 B-lines in one intercostal space that can be seen at any moment during a respiratory cycle.
Alveolo-interstitial syndrome (AIS): This syndrome is defined by a B-profile, as described by Lichtenstein DA and Mezière GA in their 2008 study: "Relevance of Lung Ultrasound in the Diagnosis of Acute Respiratory Failure, The BLUE protocol" published in Chest (2). The B-profile will have two separate, positive zones for B-lines, as previously defined, bilaterally.
Lung US profiles. From Lichtenstein DA and Mezière GA, Relevance of Lung Ultrasound in the Diagnosis of Acute Respiratory Failure, The BLUE protocol. (2)
Role of POCUS in Diagnosing ACPE
The sensitivity of POCUS for AIS is around 97% with a specificity of 95%. Considering that previous studies looking at the test characteristics of CXR, which is used on a daily basis for this purpose, showed a sensitivity ranging from 50 to 70% for AIS as interpreted by a Cardiologist, these figures are quite impressive.
The differential diagnosis for AIS, however, includes a variety of lung conditions not just ACPE but also acute respiratory distress syndrome, interstitial pneumonia and diffuse parenchymal lung disease, as described by the International evidence-based recommendations for Point-of-Care lung ultrasound, published in 2012 (3). So the clinical context of the scan is as important as the scan itself.
In terms of technique to elicit the B-profile, the best method was described by Volpicelli et al. in 2006. They described an 8 zones technique, 4 zones on each side of the thorax, as shown below:
These patients all presented with acute dyspnea and a suspicion of ACPE, which is pretty similar to our population in the ED. There was no restriction on the protocol, machine or operator performing the scan used as long as they used B-lines to make the diagnosis and the physicians performing the scan was a non-radiologist at the bedside.
How about integrating cardiac views as well?