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

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