Hi all, this week's VOTW is presented by Drs Forrest, Yang and Schiller!
A 71 year old male w/ hx of COPD presented to the ED for altered mental status. He was found to be obtunded due to hypercapnia and was intubated in the ED. Several hours after admission to the MICU the patient suddenly desaturated to 64%.
A POCUS was rapidly performed which showed…
Clip 1 shows a POCUS of the R anterior chest. On the left side of the screen, the pleural line has absent lung sliding. From the right of the screen, normal pleura with lung sliding is seen coming into the image with every breath. This is a “lung point” which is the exact point at which the pneumothorax starts. A chest x-ray confirmed a large R sided pneumothorax with mediastinal shift. A chest tube was placed by the ED team for a tension pneumothorax with improvement in vitals.
Image 1 shows an M-mode image obtained expertly by the team at the lung point which shows both "seashore sign" indicative of normal lung as well as "barcode sign" indicative of pneumothorax in one clip. You'll see this only if you use M-mode at the lung point.
M-mode showing areas of “sandy beach” alternating with “barcode sign” at the lung point
Lung sliding
In normal lung, the pleural line will appear to shimmer due to the movement of the visceral and parietal pleura sliding against each other. With a pneumothorax the contact between the two pleura are lost and the pleural line will appear still.
*The presence of lung sliding rules out a pneumothorax at the location of the chest you are scanning.
*Image the least dependent site (where air is most likely accumalate) to maximize sensitivity of the test (anterior chest in a supine patient).
*Reduce your image depth all the way! This way you don't have to squint while looking for lung sliding
Lung point
This is the point at which normal lung sliding and absent lung sliding are seen next to eachother simultaneosuly and is the exact point where the viseral pleural is peeling away from the parietal pleura. If found, this finding is highly specific for pneumothorax. It won't be seen with a large pneumothorax that envelops the entire lung.
Does absence of lung sliding always indicate pneumothorax?
No. Absence of lung sliding can be seen with many conditions including a bleb from COPD, right mainstem intubation (no left-sided lung sliding), patients w/ previous thoracic surgery (such as pleurodesis or VATS), pleural adhesions, ARDS, pulmonary fibrosis, atelectasis, and phrenic nerve paralysis. If the patient is stable, confirm the diagnosis with a chest x-ray or CT prior to placing a chest tube.
Which lung ultrasound artifacts rule out pneumothorax?
A-lines are reverberation artifacts that can be generated by air in normal lung tissue or air in the pleura so cannot be used to rule out pneumothorax.
B-lines indicate the presence of interstitial edema which can only be seen if the lung tissue is abutting the pleura. Even seeing one B-line is enough to rule out pneumothorax.
Happy sliding,
Your Sono Team