Pneumothorax, power Doppler

Images and Text Genevieve Carbonatto

You get an ambulance call. A 34 year old man has fallen off a roof and has severe left sided chest pain. He will be arriving in 5 minutes.

The patient arrives. He has significant chest pain which is localised to his left lateral chest wall but he also has anterior right chest wall pain. The pain is worse on breathing. He is saturating 94% but breathing is very shallow. You do an EFAST exam. Because of his symptoms you start with examining the chest.

This is his right lung ultrasound using a curvilinear probe.

You are looking at the pleural line for lung sliding and also looking at the space below the pleural line for “shimmering” which would indicate that a pneumothorax is not present. In the heat of the moment you are not sure that there is lung sliding and you wonder whether there might be a pneumothorax. His breathing is very shallow because of his pain and therefore there is little lung movement. To check whether there is lung sliding, you have 2 options. You can use power Doppler or you can change your probe to a linear probe. Changing the probe will give you beautiful clarity of the pleural line, with power Doppler you don’t have to change the probe and you can confirm lung sliding. You turn on power Doppler.

Here lung sliding is definitely present. You decide to change to the linear probe anyway and this is what you see

The pleural line is beautifully visualised and there is no doubt that there is lung sliding

You switch to the left side of the chest

This is the ultrasound using the curvilinear probe

It looks like there is no lung sliding. You add power Doppler.

The pleural line does not light up and there is no lung sliding. This is the ultrasound of his left chest using a linear probe

Definitely no lung sliding

Discussion

False positives and false negatives are not uncommon in the trauma situation. False positives have been much more frequent than false negatives in our experience. This has possibly to do with the fact that as a treating physician you are expecting the worse and somehow primed to find an abnormality. Lung sliding is sometimes subtle in a patient who is experiencing severe chest pain from a fractured rib for example as they will want to splint their chest as much as possible. It is worthwhile checking your findings if they are “equivocal” by using other modalities such as power Doppler. The problem with power Doppler is that your hand has to be very steady so that you do not have motion artifact from your probe. In our experience switching to a linear probe is the best way of identifying lung sliding. Power Doppler requires ultrasound operator skills which are not always available to the treating physician.  The “seashore sign” on M mode when  lung sliding is present and  the “stratosphere sign” when a pneumothorax is present is useful, but even then hand motion and patient movement may give false positives in the case of a pneumothorax. We believe that the best way of identifying the absence or presence of lung sliding is by switching to a linear high frequency probe if there is doubt using a curvilinear probe.

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