So much so, in fact, that I did a study on it. Previously, I was pretty much a hater for using m-mode in the evaluation of a pneumothorax. In fact, many publications that speak on the topic report that m-mode is a useful adjunct in the evaluation of a PTX. M-mode (or motion mode), is a technique that previously was taught to be useful in the evaluation of a PTX. That gravely appearance of the “beach” represents movement of the pleural line. If you get a “sandy beach” or “seashore” sign, you’re seeing movement of the pleural line, implying the absence of a PTX. If you get a “stratosphere” or “barcode” sign, it means that the US machine isn’t detecting any movement of the pleural line, and implies PTX. So to get the proper m-mode picture, you’ll place the m-mode marker over the pleural line in an intercostal space. Instead of playing a real-time image, what it does is it graphs out time, in the x-axis, over movement and depth in the y-axis. M-mode is an alternative way for the ultrasound machine to interpret what it hears. 9 Make sure you look at all of the lungs, including laterally and superiorly, since you can only rule out a PTX in the rib space you see lung sliding. 7 Lichtenstein found that 38% of supine patients with PTX had the PTX localized in the lower half of the lung (the rest had it over the entire anterior wall, including the lower half). One study found that in supine trauma patients, most pneumothoraces were seen in between rib spaces 5-8 bilaterally, not the commonly taught 2nd-4th IC spaces. In supine patients, you should start your evaluation around rib spaces 5-8. Let me explain: if you have a patient that isn’t in extremis, you should probably make sure to look at whatever part of the chest is most anterior. 8 However, if you want to increase your sensitivity, you might want to look a bit lower. A PTX large enough to cause shock is very unlikely to not be identified there. 7 If you have a hemodynamically unstable patient in whom you suspect a PTX as the cause of said hypotension, you can pretty much look anywhere in the anterior chest wall. Most of the current literature teaches that the evaluation for PTX should begin between the 2nd-4th ribs at the mid-clavicular line.

The table below shows other conditions that can cause there to be a lack of lung sliding. That being said, in most of the patients we will be seeing, the absence of lung sliding might not be good enough to use in clinical practice. If you have a 32 year old triathlete that was in an MVC and has a seatbelt sign that has no lung sliding on one side, you can be fairly certain that lack of lung sliding is due to a PTX. 4,5 When you don’t see lung sliding, it’s not quite as useful. When lung sliding is seen, it has been reported to have a negative predictive value of 100% for ruling out pneumothorax at that interspace. Lung sliding is most useful when you see it. Even though the visceral pleura might be 1 mm or 100 mm below the parietal pleural there will be a layer of air between them, making that visceral pleura invisible to the ultrasound machine. So you will be seeing the parietal pleura (which is stuck on the ribs) without the motion of the visceral pleura just underneath it. Now, when you have a PTX, the visceral and parietal pleura will be separated by air, which blocks the sound waves from reaching the visceral pleura. Why do you always have that same white line even if you do or do not have a PTX? Well, when the pleura are opposed the distance between the two lines is too small for the machine to pick up their signals individually, but what it can detect is the relative motion between the two. If that white line is not moving, you may have a PTX. If you see that white line moving, the visceral and parietal pleura are touching (no PTX).

What you’re evaluating is the back and forth movement of that white line. By merely looking at the line itself you won’t be able to tell if there is a PTX, because it’s appearance looks identical in both a PTX and without a PTX. This white line will always be there, and represents the visceral-parietal pleural interface (if there is no PTX) or just the parietal pleura (if there is a PTX). With the probe in the sagittal orientation, identify the ribs in cross section, and look for a white line underneath them. There are 4 signs you can use to help you in the evaluation of a PTX:

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