Intensivist and Emergency Bedside Ultrasound Evaluation for Pneumothorax - SD

Introduction

I'm Anthony Dean.
I'm faculty at the University of Pennsylvania in Philadelphia, in the Department of Emergency Medicine.
And I run our ultrasound program here.
And this is one of the applications of ultrasound that is extremely useful in rapid assessment, both of trauma patients, as well as others with unexplained shortness of breath.

Overview of the Lecture

In this lecture, we're gonna talk about the evaluation for pneumothorax.
Just to recap, overall we've been looking at the heart, the IVC, the lungs, and the pleura in critically ill.
And so in this particular hour will focus on the evaluation of the pleura for pneumothorax.

Goals of the Lecture

The goals of the lecture are going to be to understand the anatomy and sono anatomy of the pleura, to understand the technique of how pleural evaluation is done.
Think about some of the caveats and pitfalls of the exam.
And we'll look briefly at the science behind this as well.

Fundamental Concept: Lung Sliding

The fundamental concept in pneumothorax is that of lung sliding, also known as pleural sliding.
And the basic concept is that the ultrasound can identify the two layers of the pleura moving with respect to one another.
And this is a simple assessment of the basic physiological fact that during normal respiration, the visceral pleura, which actually stuck to the lung, are sliding with respect to the parietal pleura, which are stuck to the chest wall.

And here's an anatomic schematic of this showing the two layers, the visceral and parietal pleura intimately opposed, and obviously only separated by a potential space, in a normal, healthy person.

This is a cadaver specimen right here, showing this.
Now in detail, you can see a little bit more clearly here.
This is actually the lung.
Again, it's a cadaver specimen, so it appears like a solid organ.
It's presumably filled with blood postmortem.
But this actually is the space, the location of what we're going to looking at.
And you can see that these two things are a very small fine line, and that the surrounding anatomy includes the sternum right here.
And we'll also see some ribs out here in addition to the musculature of the thoracic wall.

Technique for Pleural Evaluation

To start with technique, we're going think about where we place the probe.
The probe is going to be placed in the mid clavicular line, in a longitudinal direction.
So it's going to be straddling the ribs.
It'll be at right angles to the ribs.
The depth and focus should be adjusted, especially if this is being done after a focused assessment by sonography and trauma, a fast exam.
'cause in that exam, deeper cavities in the body are examined, and now we're examining relatively superficial structures.
The maximum depth from the skin to the pleura, even in a very heavy person, is about five centimeters.
So the depth should be adjusted accordingly.
And here you can see the focus has been adjusted as well at the correct level.

Identifying Ribs and Rib Spaces

The second thing after the probe has been placed is to identify the ribs and the rib spaces.
And again, when starting this, developing this skill, it's quite easy to be thrown off by many of the other lines that actually appear like the pleural line.
So it's important to have a systematic, thorough approach to this.
The ribs are identified by their echogenic surfaces here and their shadowing, the shadows are jump out at you visually, and it's very helpful to assess, to identify these actively in your mind before moving on to try and figure out where the pleural line is.
Here, the surface of the rib, we mentioned that.
And the correlate here with the cadaver model is shown with the ribs coming around here in this transverse section.
And the cartilaginous area up here.
But basically, the ultrasound probe is traversing between two of these rib spaces, giving you this image here.

Here's another image, with slightly different technique, but again, the shadowing is what's gonna lead your eye towards recognizing the ribs.
And from there, we're going to identify the pleural line, which is in this rib space, is found in the rib space, but it's immediately under the ribs.
Again, looking at these two still shots, you can see how many lines that your eye could be confused by.
But if you focus on the ribs here and here and see them, the outer surface of the rib, you can be, it's intuitively obvious that the inner surface is about this depth here.
And so this is the line that you're going to be focusing on in this image here.
Again, in large number of lines that could be confusing.
The one that you're going to identify is the one that actually goes under the rib.
And you can see this rib, there's some through transmission of the ultrasound on this rib, which actually shows you the posterior surface.
So here you can be very confident that this is the pleural line on this rib.
Again, in this rib, a little bit more typical in that the shadowing prevents you from seeing the posterior wall of the rib.

The pleura line will be parallel to the skin and the probe interface.
So this, the line we're looking for is gonna be approximately parallel with this line here, the probes on the surface of the skin.
And here it is once again.
Another example, here we have two ribs.
Here's the under surface, this rib and the under surface, this rib, which can be seen.
This is the pleura line.
And right here we have a dynamic image showing the same thing, two ribs with shadowing, and again, the posterior surfaces of these ribs that actually can be seen on this ultrasound.
So we know we're looking for this line here.

Making the Diagnosis

The fourth and final step is to actually having identified the pleural line, make the diagnosis from the information the pleural line gives you.
And this can be done by identifying normal findings, which are present in expanded lung, and thus ruling out the presence of pneumothorax by identifying, expanding lung and the finding the normal findings are pleural sliding.
And conversely, if you have absence of pleural sliding that rules in pneumothorax, there are two other subsidiary findings, which could be used to make the diagnosis too.
But as we see, they're really just special cases of these two simple concepts, pleural sliding or the absence of pleural sliding in a normal, non pneumothorax lung, it might be possible to identify pleural based comet tail artifacts.
We'll discuss these at much greater length in the lecture covering abnormalities of the lung.
But we'll discuss, but they're actually helpful occasionally in the pneumothorax exam.
And then there's also a possibly identifying the leading edge sign, which rules in pneumothorax.

So two things can be used to rule in normal lung sliding under the probe.
And two things can suggest there is a pneumothorax right under the probe.

Normal Findings: Ruling Out Pneumothorax

To start out, we're gonna rule out the diagnosis rule in normal and identify pleural sliding.
Secondly, we, if we also might be able to identify pleural based comet tail artifact.

Pleural Sliding

So here we see a case of pleural sliding.
Again, one of the first things to do is to make sure you're looking at the pleural line.
Again, there are several lines here that might lead your eye astray, but in this case, you can see the rib here with its good strong shadowing, intuit that right under here, somewhere under here would be the posterior side of this rib.
And see this line sliding up under the rib, this rib cannot be seen very well at all.
But this line here is the pleural line, and it can be seen to be sliding back and forth in this direction with respect to itself.
This is pleura sliding and represents the visceral pleura sliding with respect to the parietal pleura on the chest wall.

Here's another case, two ribs in here.
And we're looking at this line right here, this line, this clip is actually demonstrating the technique that's used in real time, which is examining each space, which we'll discuss in a few moments.
But once again, in this slide, please notice the clip showing this sliding motion in each rib space.
And note how we hold still very, very still.
While we appreciate the pleural sliding before moving on, this is normal expanded lung showing pleural sliding.

Here's another example. Rib shadow, rib shadow.
And here we have the pleural sliding in this, along the pleural line.
And again, notice how there are apparent lines, some faint ones behind this pleural line, as well as in front of the pleural line, which could be mistaken, but this is actually the pleural line right here on the slide.

Comet Tail Artifacts

So the second way that we can rule out the diagnosis of pneumothorax by ruling in the normal is by identifying pleural based comet tail artifacts, which are also known as lung rockets.
Comet tails or lung rockets are the way they usually described.
And basically, these are caused by irregularities or air fluid-filled alveolar walls right under the pleural, right under the visceral pleura that cause reverberation.
And their presence indicates that the visceral pleura is indeed abutting the parietal pleura and causing this artifact.

So, while comet artifacts are caused by abnormal fluid filled lung next to the pleura, even though this is an abnormality with respect to the lung, it actually means there is no pneumothorax.
So when you're focusing on whether or not there's pneumothorax, these things help you rule it out.
But since many people have non-disease lung, the absence of comet tails does not mean that you have a pneumothorax.
So presence of comet tails means that you can rule out pneumothorax.

Here's a clip showing comet tails.
And again, really, even though we can't see the ribs here, we can identify this, the pleural line.
We can see the pleural sliding.
And the comet tails really just emphasize in a sense the sliding, because it makes it even more obvious by this reverberation.
That's coming down from the pleural line.

Abnormal Findings: Ruling In Pneumothorax

So now we're gonna consider the way that pneumothorax is ruled in.
The first way that pneumothorax is ruled in is the opposite of what we just described.
It's the absence of pleural sliding anywhere on the chest wall.

Absence of Pleural Sliding

And once again, a clip here showing rib shadow, rib shadow posterior rib over here, actually shown.
So this is the pleural line.
You can see it going underneath this rib here as well.
But this pleural line here, even though this some motion of respiration is not sliding back and forth in this direction here, this motion in this direction just represents changes of intrathoracic pressure.
And does not is not the same thing as the pleural sliding caused by the immediate opposition of both layers of pleura.
This is a pneumothorax right here.

Absence of pleural sliding is another case. Rib shadow.
Rib shadow. This is going to be our pleural line.
And we're going to be interrogating this line right here to see if we can see any sliding, as can be seen from this clip.
There's some hand movement here, which makes it harder to appreciate the absence of sliding, 'cause any movement up here also appears like the pleura is moving.
We'll talk about this a little bit further when we discuss technique.

Lung Point or Leading Edge

So the second way that we can actually rule in pneumothorax identify it positively is by identifying the leading edge of the lung point.
The lung point, or the leading edge is that spot of the lung which makes the transition between expanded lung, which would be over here and collapsed lung, many pneumothoraces are not complete so that there's an area of the lung that has fallen away from the chest wall, but another area that is still in contact with the parietal surface of the body.
And the transition zone between those two things is the point of the lung.
Point is the identifiable spot called the lung point or the leading edge.
If you put a probe over there, you'll see that transition.
And what that looks like is an area of the pleural line.
Here we are rib shadow, rib shadow pleura line.
But in this clip, you can see that for much of the clip, there's no sliding.
And then right here across comes an area of lung that's sliding back and forth.
So this transition between no sliding and sliding is the lung point.
And this indicates that there is, in fact, a pneumothorax.

Is another case right here.
Rib shadow, rib shadow here, and rib with shadow right here.
So this is the line we're looking at here.
And in this image, we have to look very carefully, but there's no movement here.
Periodically. There is a fine flicker of movement right through here, and that's as the lung moves up and backwards right here, coming to contact with the chest wall, right there, it comes and goes back, no movement.
Here comes the flicker of movement right here, and no movement, flicker of movement right there.
And then no movement, flicker of movement right there.
And the lung withdraws from the air into the area of pneumothorax.
The lung point is the transition point, an expanded and collapsed lung.

Scanning Protocol

So how much of the chest should be scanned?
And the essential answer to that is the midclavicular line on each side of the chest from right immediately inferior to the clavicle, down to the diaphragm.
The scanning should be systematic and thorough as usual.
And this is obviously a real time test requiring real time interpretation of the moving gray scale images.
Although there is a technique for recording this and identifying it using m mode, which we'll discuss in a moment, if the heart's encountered in many patients, the heart comes over into the mid clavicular line, then the probe is moved further laterally, and the rest exam is completed probably in the anterior axillary line.

Choice of Probes

What probes can be used?
It's really up to the sonologist to find out which he or she finds works best.
Certainly the linear probes, you higher resolution and might be anticipated to give you a more clear defined picture of the pleura, which is obviously a fairly fine structure.
And since this is a very superficial structure.
The linear probe is well suited to that.

And here is an image provided by linear probe, which I think we've seen before, of absence of lung sliding right in here, and somewhat pixelated image.

Oftentimes though, even though the curved array probes are a little, have a little less resolution and not designed oftentimes primarily to work at such shallow depths, the curved array probe often seems to exaggerate the movement of the pleura by causing faint little lines that could be clearly seen.
Moving across the screen with the angle created by the curved array probe, they sweep backwards and forwards here.
And sometimes people find it easier to use a curved array probe for that reason.
A tight array probe, or a loosely curved array probe works very well usually at the upper range of its frequency.
And as mentioned before, with the focus adjusted for superficial structures.

It is possible to see pneumothorax using the phased array probe.
And this shows lung sliding very nicely here.
The phased array probe is designed to go between the ribs.
So oftentimes, especially for beginners, it's a little harder to be sure of where the pleural line is because the ribs are actually avoided by this probe, this very narrow footprint.
In addition, many phased array probes are not so well equipped to identify near field structures.
So sometimes if you have alternative probes, the ones we've mentioned already, it might be easier to use them.
Since this exam is frequently done after fast exam, most people end up using the probe that they've used for the fast exam to perform the exam of the pleura.
And that's something of a pragmatical consideration.

Caveats and Pitfalls

It's important to remember that lung sliding only rules out pneumothorax under your probe.
So it's if you look at someone with a small pneumothorax like this, it's quite possible that you'd have an area where there is lung sliding seen, and then an area where there's no lung sliding.
And then an area back here where there is lung sliding.
Most people, if they don't have pleural scarring, if they're lying in a supine position, will, regardless of where their pneumothorax is when they're standing, will form a space of the pneumothorax anteriorly just due to the weight of the lung falling away from the anterior chest wall.
Nevertheless, lung sliding, it should be remembered only rules out pneumothorax under the probe.

One another caveat is obvious thinking about this, that leading edge is not seen in most pneumothoraces because it's a relatively small area of the entire pneumothorax that actually demonstrates this transition point between expanded and collapsed lung.
So the absence of leading edge does not rule out pneumothorax by any means.
Its presence only rules it in.

Technique Considerations

In terms of technique, a really important skill when starting out and as one is performing this exam is really steady anchoring of the hand on the skin.
And what that requires is that the fingers, oftentimes two or three fingers are slid down here along the edge of the probe and held in contact with the skin.
And if it's comfortable, the pinky finger can also be used to stabilize the probe.
A good exam should demonstrate complete lack of movement of this area here, the subcutaneous muscular tissues, so that the eye can focus on the presence absence of movement here.

This is actually a person with a pneumothorax in the case we've seen before.
But the apparent motion of this every now and then is actually accompanied always by motion up in this area here, so that this is actually artifactual motion here.
There is no lung sliding, and this is actually a pneumothorax.
But if the examiner held the hand steadier and more carefully positioned on the chest with the hand stabilized as described over in this picture here, this pneumothorax would be much easier to appreciate.

Cardiac motion. The diaphragms can cause problems, may be confused with pleural sliding, creating the impression of false negative in someone who has a pneumothorax.
And conversely, it may be confused with a leading edge, which will give you a false positive exam in someone who actually doesn't have a pneumothorax.
And right here, we can see something that almost looks like a leading edge going forward and backwards here, but carefully examination of this image shows that when this piece of lung slides back, there is actually still an area here with the same beating motion.
And this is obviously the heart.
It's also interesting to see how the heart does create transmitted movement all along the pleura in the surrounding lung.
And that's normal.
And certainly it's a little bit easier to figure out when one's actually got one's hand on the probe and the appropriate location on the patient's body.
Compared to a clip like this where the viewer is not certain exactly where the examiner has their probe positioned on the body, similar effect can be caused by the diaphragm sliding up and down.

And again, these things can be more confusing, partly because the depth is adjusted so superficially that the underlying structures are not immediately recognize the liver, the spleen, et cetera, are not nearly so easily recognized as a result of being viewed in such proximity.

Once again, movement is identified.
And right here we have some movement here caused by the diaphragm.
This is actually not a leading edge and is not a pneumothorax down here.
This is just the edge of the lung sliding up and down right next to the diaphragm.

Other Pitfalls

Other causes of false negative exams, the small localized pneumothorax is probably the most common one.
And we'll talk about the sensitivity of the test, but CT definitely identifies some small pneumothoraces that are not identified both by chest x-ray and by the ultrasound.
If one has a high index suspicion for pneumothorax, it's important to do wide scan wide area, and if necessary, scan areas outside of the midclavicular lines, the I've described as being sort of the basic essential component of the exam.
But if there's a question of high suspicion in pneumothorax anywhere on the chest can legitimately be scanned, looking for absence of sliding.

Another pitfall that was revealed by Dr. Kirkpatrick in his series was that we have a tendency to compare one hemithorax with the other when we do this exam.
And a significant proportion of the pneumothoraces that were missed in his series were bilateral pneumothoraces.
And in bilateral pneumothoraces, one or both sides had a tendency to be missed.
And so this is someone who has significant trauma.
The possibility of bilateral pneumothorax should be considered, and one should try to avoid relying too heavily on comparisons from one side to the other.

A cause of false positive exams is pleural scarring adhesions, COPD and lung disease.
Anything that causes the two layers of pleura to either not slide or to be not so clearly visible might give the impression that there is no lung sliding.
And as a result that there is a pneumothorax present a lot of the time.
The examiner, the clinician will be aware of the likelihood of this by the appearance of the patient, the age, the habitus, et cetera.

We'll discuss a lines more closely in the lecture on the lung.
But the absence of lung sliding and the presence of a lines, which are the comet tails we've mentioned, allows a very high degree of confidence that pneumothorax is ruled out.

Patients with chest wall injuries might be unwilling or unable to make good respiratory effort.
And absence of pleural sliding might be thought to exist in someone who is not making proper respiratory effort or a splinting on that side due to injuries.
So this is something that should be considered in such context of trauma.
Obviously intubated patients can be given sigh breaths to help air movement and pleural sliding.

Comet tail artifacts, as we've said, rules out pneumothorax under the probe.
But this should not be expected in most acute trauma patients.
So in one series reported by Dr. Dulchavsky, there were no comet tails seen in an entire series of 382 consecutive patients.
Conversely in critical care units, comet tails are seen in the majority of patients because obviously a pulmonary pathology is much more common in that setting.
So comet tails are probably less use in the acute setting than they are in critical care.

Documentation

There maybe a need for still image documentation for reimbursement or for medical-legal reasons.
But the core of the diagnosis of this is really made in real time using video clips.
Certainly video clips can be saved to document the findings as we've seen in this lecture.
But another method that's been described is using m mode, and the movement of the lung back and forth here, and the movement within the lung underneath the visceral pleura here creates this rough appearance here, which often described as waves coming up towards the shore in this direction here, waves on shore.
And this indicates the absence of pneumothorax.

Conversely, when a pneumothorax is present, the lines tend to be much more smooth and give you this these linear kind of this linear kind of appearance.
And which has been described as a stratosphere sign.
The presence of this on m mode suggests the presence of pneumothorax.

Is an example demonstrating in real time the development of the waves on the shore sign from someone with expanding lung here.
The real sliding can clearly be seen, and the associated irregularities within the lung fields can be seen clearly here.

Scientific Evidence

The science backing this up in the 1990s, several papers showed accurate diagnosis of pneumothorax in basically in medical patients, in critical care units.
It was also used to assess for iatrogenic pneumothorax after thoracentesis or other pulmonary investigations, and a number of different signs and techniques were described.
But really, as more and more data emerged, the presence or absence of lung sliding, with or without comet tail artifact, as emerged as the single reliable predictor of expanded lung and thus of pneumothorax.

In 2001, there's a prospective study clinician performed ultrasound in stable trauma patients that plain films with the gold standard, as we've discussed before, and in this series, sensitivity was very high at 95%, and there were no false positives.
And false negative evaluations were patients who really were unable to have an effective ultrasound evaluation because they had subq emphysema.

Other studies have really since then shown that this high degree of accuracy has not been born out in most people's clinical practice.
In this large series done by Dr. Kirkpatrick in 2004, there was a sensitivity and specificity about 50 and a hundred percent.
This test gives far less false positives than false negatives.
And it was compared to chest x-ray with a composite endpoint, including ct, which and it was about twice as sensitive as chest x-ray.

In 2005, another study actually appeared to show that the sensitivity specificity of emergency ultrasound was extremely high, almost a hundred percent.
And chest x-ray in this series was also much higher than has been reported elsewhere.
And in this study, there's also an estimation of the size of the pneumothorax.

At our center, we also did a fairly large prospective study with over 600 patients.
And we also found similar to Kirkpatrick, that the sensitivity of the test was about 57%, a little bit better than half.
And there were very few or no false positives in our series.
And we found that the ultrasound, again, was about twice as sensitive as a chest x-ray.

We also assessed the learning curve and found that there actually appeared during the people's evaluation of the pneumothorax through different with a different amount of experience.
The first 10 scans, we found the sensitivity of the test was 40%.
And actually we had a very apparently strong linear relationship between the number of scans performed to do this and the sensitivity of the operator.
Again, we found that that specificity was almost a hundred percent in our series.

Review and Summary

So just by way of review, it's good to go through the choices here so that in the heat of the moment, it's easy to recognize what's happening.

If pleural sliding is seen, then the diagnosis is no pneumothorax.
And once again, it's important to emphasize under the probe.

If there's an intercostal space with absence of pleural sliding, the diagnosis is simply pneumothorax.

If pleural based comet tail artifacts are seen.
And once again, this rules out pneumothorax, but only under the probe.
So once again, it could be pneumothorax elsewhere.

And once again, if no pleural based comet tail artifacts are seen that the diagnosis is indeterminate, has no bearing on the presence or absence of pneumothorax, and it's necessary to look for pleural sliding over the rest of the thoracic cavity.

Obviously if a leading edge is seen, the diagnosis is pneumothorax.

The absence of leading edge. Conversely, if one does not see a leading edge, the diagnosis is that really has no bearing on the presence or absence of pneumothorax.
And the rest exam should proceed looking for pleural sliding.

If a dark space is seen below the pleural line, the diagnosis is actually hemothorax or some other cause of pleural fluid.
In the trauma setting, it's likely to be hemothorax, but in other settings, obviously medical causes of pleural effusion are more likely, and this has no bearing on the presence absence of pneumothorax.
Once again, the rest of the lung, especially the anterior space, should be checked for pleural sliding.

A bright echogenic pleural line has no bearing on the presence of absence of pneumothorax.
So that's not part of the evaluation.

Case Examples

And here's a few cases just to review.
Right here we see, we don't have the ribs to help guide us, but this is fairly obviously the pleural line here, quite different from the overlying soft tissue.
And there can definitely be appreciated.
Pleural sliding here. This is, this rules out pneumothorax under the probe.

Here we have rib shadow, rib shadow, and we're not seeing pleural sliding here.
So this is actually pneumothorax right here.

We have rib shadow and rib shadow.
So we're going to be looking at one of these three lines here.
And most likely it's this line here that goes under the probe.
It's possible this is a reverberation.
Yeah, I think this is a in fact a reverberation artifact right here, this lower line.
So this is actually the pleural line, the middle of these three bright lines here.
And the reason I can be sure of that is that there is no pleural sliding, but every now and then, there's a flicker that comes across here, which would be the lung point or the leading edge sign, indicating that this person does indeed have a pneumothorax.

In this slide here, we have a rib apparently here without the clear undersurface, but the shadowing is clearly appreciated.
We don't have a rib to be seen here.
And it's really hard to be sure of what this exam reveals.
It's questionable.
There might be a flickering here of a lung point.
We're really not seeing very clear clearly defined pleural line.
And it's possible that down here we're actually looking at subdiaphragmatic structures.
So in cases such as this, it's quite legitimate to say that you've had a limited or inadequate study, and proceed with your exam and look elsewhere or document that you were unable to make a definitive conclusion based on your exam.

Here we have a rib with a shadowing, another rib with shadowing over here, and right here, pleural sliding, can easily be appreciated.

Conclusion

So that's the conclusion of this section on pneumothorax.
And if there are any questions or comments for this, you can certainly contact www.sonoworld.com to communicate them with me.