Normal Lung Ultrasound
This lesson will cover the standard locations for lung ultrasound and the normal findings in those locations.
Probes and settings to use:
- any probe can be used in the anterior position
- if focusing on the pleural line, then a depth of 6 cm should vertically center the pleura on the screen
- the cardiac (phased array) or abdominal (curved array) probe must be used for posterior or lateral positions because the required depth is too much for the vascular probe
- The patient may be examined in a seated or supine position
- A seated position is usually easier for assessment of the posterior thorax
- The probe is oriented in a longitudinal orientation (probe marker pointing to the head)
- The thorax must be examined in a systematic manner to look at all lung regions
- Different lung scanning protocols have been described
- Two common protocols are presented: the "BLUE points" and the Volpicelli method
- Superiority of one specific protocol has not been demonstrated
- The examiner should take care to ensure the ultrasound probe is positioned exactly perpendicular to the pleura to maximize pleural line echogenicity and generated artifacts.
The “BLUE Points” Method
- Identify four anatomical points on each hemithorax (there will be a total of 8 points with both lungs).
- Point 1: upper anterior chest wall, 2nd rib space, mid clavicular line.
- Point 2: anterior axillary line, 5th rib space (nipple line). This examines the middle lobe on the right side.
- Point 3: mid-axillary line at the level of the diaphragm.
- Point 4: is the PLAPS (posterolateral alveolar or pleural syndromes) point immediately posterior to point 3. Press the probe as posterior as possible into the bed while maintaining a perpendicular orientation to the skin.
Figure 4. Blue Points. Image modified from Lichtenstein, et al.1
The Volpicelli method: this is similar to the Blue Points, providing 4 zones, each requiring a single examination region on each hemithorax, for a total of 8 points for a full thoracic exam.2
Volpicelli protocol with 4 areas in each hemithorax. Taken from Volpicelli, et al.2
PSL = parasternal line
AAL = anterior axillary line
PAL = posterior axillary line
Normal Appearance, Anterior Scanning Location: scanning depth should be 10-12 cm. but can be much less too (image below is 4 cm deep)
The top (superficial) portion of the image will consist of fat, muscle and bone (the chest wall).
The pleural line is very important to identify:
The ribs will cast shadows. These are artifacts. The rib shadows are outlined by the yellow lines below:
Many ultrasound images look like other imaging. Here, you can see that a CT of the heart can look very similar to an ultrasound. Tissue looks like tissue and chambers look like chambers:
Lung ultrasound is different and is about artifact analysis. Air does not transmit ultrasound waves. It will scatter them.
As a result, EVERYTHING we see below the pleural line "inside" the lungs is artifact (bottom blue zone). Can you see a "fake" mirror image of the ribs inside the lung? Everything we see above the pleural line are true images of muscle, fat and bone.
- lung sliding is a normal finding and should be observed
- requires the visceral pleura to be moving relative to the parietal pleura
- requires these 2 pleural surfaces to be in contact with each other
- relative to the ultrasound probe, the chest wall does not move, but the lung does
- the lung can be seen moving left and right with inspiration and expiration
Here is a video example of lung sliding:
Absence of lung sliding occurs when:
Normal Appearance, Posterior and Lateral Scanning Locations:
- the 2 pleural surfaces are not in contact with each other:
- pleural effusion
- the lung is not moving relative to the chest wall:
- the lung is adherent to the chest wall
- the portion of lung that is imaged is not being ventiltated
- endotracheal tube is in contralateral bronchus
- lung is full of pus (severe pneunomia)
- advanced bullous COPD
The images below are taken from the patient's right side, so the liver is seen:
- scan depth should be 14-16 cm
- scanning in the posterior zone needs to include the diaphragm
- on the right, the liver will be seen below the diaphragm
- one the left, the spleen will be seen
- kidneys will may be visible as well
- the spine can also be visualized at deeper depths
The image below is from the patient's left side, showing the spleen. The spleen and liver are similar (but not identical) in appearance:
Summary of normal lung ultrasound:
- use an organized approach to view 4 locations on each lung
- anterior view must highlight the ribs and pleural line
- posterior views must highlight the diaphragm and liver/spleen
- all images "inside" the lung are artifact
- sliding lung is a normal finding
- Lichtenstein D, Mezière G., (2011). The BLUE-points: three standardized points used in the BLUE-protocol for ultrasound assessment of the lung in acute respiratory failure.Crit Ultrasound J. 24, pp.109-110
- Volpicelli, G. et al., (2012). International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 38, pp.577-591