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The Nuances of the Pneumothorax

There are three bedside tests we have to evaluate for pneumothorax: the physical exam, chest X-ray (CXR) and ultrasound (US).  The best one we have is undoubtedly US.  Learning the basics of this exam is fairly easy, with studies showing that it takes a small amount of didactics and hands-on, and has a very high retention rate. 1-3 That being said, there are a few nuances that you should know before basing your clinical management off of your US.

Oh, and if you need review on how to do the exam, check out this video:

 

There are 4 signs you can use to help you in the evaluation of a PTX:

 PTX_Blog_Signs3 

Lung sliding

Lung sliding is most useful when you see it. When lung sliding is seen, it has been reported to have a negative predictive value of 100% for ruling out pneumothorax at that interspace.4,5 When you don’t see lung sliding, it’s not quite as useful.  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.  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. The table below shows other conditions that can cause there to be a lack of lung sliding. 5,6

PTX_Blog_Signs2

Where to scan to look for lung sliding.

Most of the current literature teaches that the evaluation for PTX should begin between the 2nd-4th ribs at the mid-clavicular line.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.  A PTX large enough to cause shock is very unlikely to not be identified there.8 However, if you want to increase your sensitivity, you might want to look a bit lower.  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.  In supine patients, you should start your evaluation around rib spaces 5-8.  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.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).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.

 What about M-mode?

M-mode (or motion mode), is a technique that previously was taught to be useful in the evaluation of a PTX.  In fact, many publications that speak on the topic report that m-mode is a useful adjunct in the evaluation of a PTX. 5,10-13  However, the use of m-mode an accessory to the dx of PTX has no actual basis in fact.  I’m not saying it’s not useful, but there is no evidence out there saying it’s useful.  There’s only one study that actually looked at the benefit of m-mode for PTX, but it wasn’t a human study. That one study was done in cadavers and showed that using m-mode actually decreased the accuracy of the detection of a PTX.14 That’s really the only literature we have looking at the usefulness of m-mode in the diagnosis of a PTX.

 B-lines and PTX

B-lines are thought to be generated from the visceral pleura, so it makes sense that visualization of B-lines rules out PTX. 16  For the most part that is true, but there are 2 things that you should keep in mind when using this clinically.  First, make sure they’re actual b-lines and not comet-tail artifacts.  B-lines extend all the way to the bottom of the screen and move with respiration.  Comet-tail artifacts look similar to b-lines except they don’t extend all the way to the bottom of the screen.  One study found that 84% of patients with a pneumothorax had comet-tail artifacts in the area of a pneumothorax.9 Second, although b-lines have been reported to be absent in all pneumothoraces, there is one bit of information that may contradict that.  There have been a few published articles that report b-lines being present in patients with pneumonectomies.  While no definitive explanations exist, there is a prevailing hypothesis that those patients with pneumonectomies have inflammation or other changes within and around the parietal pleura that mimic b-lines 17,18

 Lung point

The lung point, which is when you have lung sliding and lack of lung sliding in the same rib space, has been NEWLungpointLabeledreported to be 100% specific for a pneumothorax. That sounds amazing, but as with most things, these findings need to be taken with a grain of salt. The only studies published that looked at the accuracy of the lung point for ruling in a PTX are both by the same author. In one publication, it was reported that out of 43 ICU patients with a PTX, the lung point was 100% specific for a PTX,and in the other, they looked at 66 ICU patients with known PTX, and also found it to be 100% specific for a PTX. 12  That’s all we have on lung point. (There is one other study that implies that the lung point is very accurate, but they include absence of b-lines, lack of lung sliding and lung point as their criteria with no mention of how each of those signs did individually 17)
There have, however, been a few case reports of false-positives. One study reported a pseudo-lung point on the left side of the chest that was due to the lung coming into contact with the heart. 20 A study by Soldati et al 19 reported that in trauma patients with suspected PTX, their one false-positive lung point was due to the same issue. Besides the border of the heart and lung, the border between the diaphragm and the lung can also create a false-positive lung point 21 Oh, and the sensitivity of the lung point is really bad so it can’t be used to rule out a PTX. 9,12  Now, I’m not saying that the lung point is useless. I look for it in all of my patients in whom I suspect a PTX.  What I’m saying is that we need more data behind the lung point before we can say that it is 100% specific for a PTX.

 Lung Pulse:

The presence of what has been called the “lung pulse” also has been reported to help rule out a pneumothorax.  This is most helpful when a patient is apneic, or if for whatever reason they’re only ventilating one lung (like in a mainstem intubation). The theory is that if the visceral and parietal pleura are connected (i.e. when there isn’t a PTX) when the heart beats, it will transmit movement through the lung to the visceral parietal pleural interface (VPPI), showing a pulse at the level of the VPPI.22 Physiologically this makes perfect sense, but you also have to take this with a grain of salt, since there’s only one study that has evaluated the accuracy of this.  The study included 15 purposefully main-stemmed patients and to 30 appropriately intubated patients.6

 When does ultrasound fail?

If you have a patient with subcutaneous emphysema, all bets are off. Air in the subcutaneous E-linetissue will cause a false pleural line with occasional “b-lines” to be generated above the pleural line, and obscure the actual pleural line.  If you see what looks like a pleural line above the ribs, there is subcutaneous air obscuring your actual pleural line.  Those “b-lines” that are generated above the pleural line have been dubbed “E-lines”.  If you see this finding, your ultrasound is pretty much useless in the eval of subcutaneous emphysema. 22 (In the gif, the highlighted blue line is the subcutaneous air) Also, it should go without saying, but if you there’s a dressing or bandage covering the chest, you won’t be able to use US either.

 Summary:

There are 4 signs you should know to evaluate for a PTX, three rule it out, and one rules it in:

  1. Lung sliding – Rules out PTX
  2. Lung point – Rules in PTX
  3. B-lines – Rules out PTX
  4. Lung pulse – Rules out PTX

 

One Response to The Nuances of the Pneumothorax

  1. charlotte says:

    Hi Jacob.
    Was caught out last week when saw clear lung sliding in a patient with a small flail and
    localised surg emphysema (lower ribs). He was seated erect and had good sliding at ribs 2-3, but at CT, had a small apical PTX tucked under his clavicle on that side. Missed it with US!

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Jacob Avila