Thoracic ultrasound is a rapidly emerging area of point-of-care sonography. There are several diagnoses which can be readily assessed using thoracic sonography:
- Pneumothorax (see other tutorial)
- Pulmonary edema
- Pleural effusion, hemothorax
- For Pneumothorax- Is the lung sliding? Is there a lung point?
- For pulmonary edema- Are there A-lines or B-lines?
- For pleural effusion- Is there anechoic fluid in the costophrenic angle?
Different authors debate theÂ useÂ of several different probe types. Curvilinear or microconvex array probes are most commonly used, though some advocate a liner probe. There are also multiple published protocols on probe placement along the chest wall. Here we will describe the zones used by Daniel Lichtenstein in his BLUE protocol:
- Zone 1 extends from the sternum to the anterior axillary line
- Zone 2 extends from the anterior to posterior axillary line
- Zone 3 is found posterior to the posterior axillary line
The probe is held in a longitudinal orientation with the marker towards the patient’s head. Look in between the ribs in each zone to see the bright white horizontal line of the pleura. The ribs will cast anechoic shadows vertically. When imaged with the probe perpendicular to the pleura, reflections of the pleural line known as A-lines should be evident in normal lung:
In contrast, intravascular lung water (as found in pulmonary edema) creates a reverberation artifact arising from the pleura. Thus, a B-line pattern is defined as multiple hyperechoic reverberation artifacts arising from the pleural line and extending towards the far edge of the ultrasound field:
Several studies demonstrate an excellent correlation of B-lines with congestive heart failure, and that B-lines can be seen to disappear within hours ofÂ appropriateÂ therapy.
Thoracic sonography can detect small amounts of fluid in the costophrenic angle, even in supine patients. It is thus well-suited to intensive care and emergencyÂ departmentÂ applications where patients cannot easily be moved. Hold the probe in the right or left upper quadrant as you would when performing a FAST examination:
With this longitudinal view, we should see liver and diaphragm on the right and spleen and diaphragm on the left side. Look above (cranial) to the diaphragm and you should see a mirror image artifact, where similar echotexture is evident above and below the diaphragm. Even small amounts of free fluid above the diaphragm obliterate this artifact with a blackÂ triangleÂ of fluid: