This IOW comes from Drs. Stephanie Khan and Hiran Patel. It captures the use of M-mode for the diagnosis of pneumothorax. A 25 yo M patient presented to the ED with acute onset chest pain and mild shortness of breath.
Take a look at the initial CXR. Can you identify the side of the pneumo? See below image IOW CXR PTHx.
Image 1 - IOW CXR PTHx
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Not convinced? Take a look at the size of the pneumo on the CT scan. See below image IOW CT PTHx.
Image 2: IOW CT PTHX
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The patient had a spontaneous pneumothorax. Let's take a moment and use this case to recall evaluation of the pleura as part of the E-FAST. In this setting, we typically look for lung sliding during respiration. The linear probe is positioned with the indicator towards the head. Adjust the probe so you see the pleura (a bright hyperechoic line) outlined on both sides by a rib with shadowing beneath. Orient the probe as perpendicular to the chest wall as possible. This will make the pleura stand out.
Sliding may be obvious, but if not, consider taking the extra steps to evaluate the pleura with M-Mode. M-mode plots depth against time, X-axis is time and the Y-axis is depth. See the below IOW Seashore Sign Image. This image shows your B-mode image at the top with the M-mode tracing beneath. The gray line through the center of the B-mode image corresponds to the Y-axis of the M-mode image. M-mode of the normal lung has been described as having a “sand on the beach” appearance. Motion within the normal lung changes the lung artifacts that return to the machine creating a speckled appearance like grains of sand beneath the bright pleural line. The soft tissues above do not move and thus have a linear appearance (the echoes do not change with time).
Image 3: IOW Seashore Sign
The second M-Mode image shows the findings of a pneumothorax. With the presence of pneumothorax, we see what is called the “Stratosphere" or "Barcode” sign. The lack of motion ver time in the collapsed lung creates a linear (almost barcode like) appearance over the M-mode image. With practice, you will be able to appreciate these subtle but important differences.
Image 4: IOW Barcode Sign
