After evaluating the pleural line, the depth will then need to be switched to 15 cm to evaluate for B-lines. If B-lines are present without lung sliding, pneumonia should be strongly considered. The appearance of B-lines with lung sliding signifies alveolar interstitial fluid, commonly from pulmonary edema.
Posterolateral Assessment
The posterolateral assessment (Figure 7) evaluates for pleural effusion and consolidation. The dome of the diaphragm is the landmark above which abnormal lung and artifacts will be seen.
Figure 8.
Summary
Lung ultrasound can help narrow the differential diagnosis for acute dyspnea within the first few minutes of the patient encounter. The BLUE protocol provides an organized approach to this evaluation. Often, the protocol is combined with focused examinations of the heart, inferior vena cava, and/or deep veins to complete the clinical picture. It is important to keep in mind that patients may have two or more pathological conditions (eg, asthma and pneumonia) that can affect the ultrasound findings. For this reason, ultrasound interpretation should always occur in the context of the clinical condition. If it does not exclude important diagnoses, additional investigations such as plain radiography, cross-sectional imaging, or ventilation/perfusion studies should be pursued.