3. Lung Ultrasound Protocol

Step 3 : Lung Ultrasound of posterior chest (R3/L3-PLAPS)

Point 3 (or R3 and L3) assesses the posterior chest. This point is commonly known as the PLAPS point on lung ultrasound (“posterior and/or lateral alveolar and/or pleural syndrome”). The PLAPS will be most relevant for assessing the presence of pleural effusions and consolidations.

  • Point your indicator towards the patient’s head.
  • Slide the probe under the patient at the PLAPS point at the intersection of the posterior axillary line and a rib space between the 10th and 12th ribs.
R3 Point - Lung Ultrasound Posterior Axillary Line
R3 – PLAPS Point
  • Identify the liver (right side) or spleen (left side), kidney, and diaphragm.
    • These organs will come in and out of view when the lung inflates and deflates.
  • You should also see the spine, which in healthy lungs, extends up only until the border of the diaphragm. If it extends past the diaphragm called the “spine sign”, you will need to look for a pleural effusion or consolidation which we explain how to do in the pathology section.
R3 Right PLAPS labeled - diaphragm lung, spine
R3 (Right PLAPS point)
L3 Left PLAPS labeled - Spleen diaphragm lung, spine
L3 (Left PLAPS point)

Curtain Sign

The curtain sign is seen in healthy and aerated lungs at point 3 (PLAPS position). An aerated lung is like a “curtain” because as it fills with air, it looks like a curtain sweeping down and over the other organs, momentarily obscuring them from view. The diaphragm, liver, or spleen reappear during exhale.

Curtain Sign on Lung Ultrasound
Inhalation causes curtain sign at the costodiaphragmatic angle

Mirror Image Artifact

Mirror image artifacts are a normal finding that occurs when reflection from a structure creates a false image behind a reflective object, such as the diaphragm, as seen in the image below. This is a normal finding in the PLAPS position.

Mirror Image Artifact - Liver, Diaphragm, Lung
Mirror Image Artifact
3. Lung Ultrasound Protocol

Step 2: Lung ultrasound of lateral chest (L2/ R2)

Point 2 (R2 and L2) examines the lateral chest.

  • Place your probe at the right (R2) or left (L2) Midaxillary line around the 6-7th intercostal space. This should be just lateral to the nipple line in males.
  • Anchor your probe between two ribs, and just like in point 1, look for the batwing sign, lung sliding, and A-lines.
R2 Point - Lung Ultrasound Midaxillary Line
R2 Ultrasound Probe Position
3. Lung Ultrasound Protocol

Step 1: Lung ultrasound of Anterior chest (R1/L1)

Point 1 (R1 and L1) assesses the anterior chest. This point will be most relevant when assessing for pneumothorax and/or interstitial edema.

  • Point your indicator towards the patient’s head.
  • Place your probe at the mid-clavicular line at the 2nd intercostal space of the right (R1) and left (L1) lungs respectively
  • Anchor your probe in the space between two ribs.
R1 Point - Lung Ultrasound Midclavicular Line
R1 Ultrasound Probe Position

Identify Two Rib Shadows (Batwing Sign)

  • The first lung ultrasound finding to confirm you are in the correct position is to look for the two rib shadows or the “Batwing Sign.” This ensures that your probe is in between two ribs.
Batwing Sign on Ultrasound

Identify Lung Sliding

  • The next finding you will want to look for is lung sliding.
  • Lung sliding is a normal finding where the visceral and parietal pleura slide back and forth on one another as the patient breathes. Some say this looks like tiny “ants marching on a line.”
  • This is a simple finding but extremely useful since lung sliding definitely means that the visceral and parietal pleura are next to each other, effectively ruling out pathology such as pneumothorax.

Editor’s Note: Lung sliding can be seen with the phased array and curvilinear ultrasound probes. However it is often times most easily seen with the linear probe given how shallow it is.

Ultrasound Lung Sliding with Linear Probe
Lung sliding with linear probe

Lung Sliding using M-Mode (Optional)

  • If lung sliding is not readily apparent, it can be further be evaluated using M-Mode. The goal of M-Mode is to see if the patient has a normal seashore sign.
  • Seashore Sign: Sky = Skin/Subcutaneous Tissue, Ocean= Muscle, Beach = Lung sliding motion (sandy appearance)
Lung ultrasound Seashore Sign - Sky, Ocean, Beach
Seashore Sign on Lung Ultrasound

Identify A-lines

When you angle your probe perpendicular to the pleura, ultrasound waves reflect off the air from the pleura and the probe surface, producing an image of what looks like pleural lines that lie equidistant to the true pleural line. These reverberation artifacts can continue reflecting back and cause several A-lines to appear before dissipating. (A1 = first A-line seen, A2 = second A-line seen, A3 = third A-line seen)

Ultrasound Reverberation Artifact - Lung A-lines
A-lines with Lung Sliding Labeled

Clinically, A-lines can indicate healthy aeration of the alveoli. However, A-lines can also be seen in cases of pneumothorax since there will be a reflection of air at the parietal pleura. The difference is that you will not see lung sliding in pneumothorax.

3. Lung Ultrasound Protocol

Lung Ultrasound Protocol

Defining the 6-Point Lung Ultrasound Exam

In general, we recommend a 6-point exam for general lung ultrasound (Lichtenstein, 2014). However, for situations when assessing for COVID-19 or other viral pneumonia, the lung can be affected in a multi-lobar manner and you should consider doing a more extensive 12-point exam.

In this section, you will learn how to position your probes properly and identify basic structures. We label the 6 lung points at our institution for easy reference and labeling on the ultrasound machines. We refer to these points as R1, R2, R3 for the right lung and L1, L2, L3 for the left lung respectively.

Probe PositionLung Field
R1 and L1Anterior Superior
R2 and L2Lateral
R3 and L3 (PLAPS)Posterior Inferior

Lung Ultrasound Labeling

Lung Ultrasound Points for a 6-point protocol
Lung ultrasound illustration in Transverse View