Pleural Ultrasonography - SD

Introduction

Hello, my name is Dr. Paul Mayo.
I am director of the MICU at Long Island Jewish Medical Center in New York City.
I'm a professor of clinical medicine at Albert Einstein College of Medicine.
I'll be talking today about pleural ultrasonography.

Importance of Pleural Ultrasonography

Pleural Ultrasonography is a key skill for the intensivist, also for the EM clinician, it's easy to learn, has immediate clinical application.
It allows safe thoracentesis.
A useful reference might be a recent clinical chest medicine review on the subject.
You could take a look at that.
And really when an intensivist or EM clinician is performing pleural ultrasonography, they have a simple question, is there a pleural effusion?
And what I'd like to emphasize is that the clinician will want to look for three cardinal features of pleural effusion.
The first would be an echo free space.
The second is this echo free space is subtended by typical anatomic boundaries.
And thirdly, that there'll be typical dynamic changes that are consistent with pleural effusion.

Cardinal Features of Pleural Effusion

Example of a Large Pleural Effusion

Here we have an example of a large pleural effusion.
We have here the chest wall, the diaphragm, the compressed atelectatic lung that represents the visceral pleural surface and their dynamic findings, which we'll get into in a moment.
The anatomic boundaries that are typical pleural effusion would be the diaphragm, the inside of the chest wall and the surface of the lung.
Once more, a large pleural effusion the diaphragm.
I faintly seen the inside of the chest wall and the surface of the lung.
The diaphragm is particularly important to identify because subdiaphragmatic device insertion may have lethal effect.
A curious but major pitfall is that the neophyte scanner may confuse the hepato renal or splenorenal recess for the diaphragm seems impossible for that to occur, but it's actually a common error of the inexperienced operator and that particular error could lead to inadvertent subdiaphragmatic needle puncture.
The examiner wants to keep in mind that in the supine, critically ill patient, particularly if they're obese or if they have a lot of ascites or high abdominal pressures, the diaphragm can be very, very high in the postcibal patient.
Sometimes there'll be the added feature of unilateral diaphragmatic dysfunction, which causes a marked elevation of the diaphragm and sometimes in the massively obese or emaciated patient, the diaphragm may actually be difficult to visualize.
However, it's the responsibility of the bedside sonographer to always emphasize, always identify the diaphragm when searching for pleural effusion and by implication when identifying an appropriate site for device insertion, always identify the diaphragm.

Identification of the Chest Wall

Identification of the inside of the chest wall is important because that tells you how far the needle will have to penetrate before it enters the pleural space.
It's nice to know that take care because some modern machines designed for a nice smooth image that's pleasing to the eye may have poor near field resolution.
There are also a variety of near field artifacts that may make it difficult to see the exact position of the inside of the chest wall.

Identification of the Lung

If a major reason to use ultrasonography is not only to identify the effusion, but to seek a safe site for thoracentesis, obviously it's essential to identify the lung in order to avoid visceral pleural laceration.
The pleural effusion, of course separates the visceral from the parietal pleura.
The clinician ultrasonographer will note that lung is compressed by the effusion.
A large pleural effusion may result in very impressive compressive atelectasis.
The lobe involved often the lower lobe, if there's supine, will be airless miniaturized.
It assumes a alveolar consolidation pattern that is tissue density.
It even has the appearance of liver.
It's become so airless and tissue dense, so-called beelines may be observed at the periphery of this atelectasis.
The lung of course, is a mobile structure.
As the ventilator cycles or as the patient moves their diaphragm, the lung will slide in and out of the scanning field.
This is termed the curtain sign and the examiner has to take care that they have a clear view of the pleural effusion without the lung sliding in between the probe in the lung because the lung could be lacerated.
Otherwise the anatomic boundaries once more.
To emphasize, here's the diaphragm outlined nicely by some subphrenic ascites.
We have an echo free space that is surrounded by the diaphragm, the inside of the chest wall demarcated by the surface of the lung.
So the diaphragm, the chest wall, and the surface of the lung subtending an echo free space.
That's an essential feature that defines pleural effusion.

Echo Free Space Complications

The echo free space may be a bit more complicated because if the pleural effusion is proteinaceous or filled with a highly cellular exudate, it may become quite echogenic.
In addition, degradation of image quality with obesity edema or heavy musculature may result in a grayness, a echogenicity of the pleural effusion.
That may be confusing.
It's not black in that case, but with highly echogenic pleural effusions, the operator may believe that there is no effusion when there actually is one that occurs occasionally, but that's not a great error.
The worse error is to believe that there isn't effusion when there is no effusion.

Dynamic Findings

The last in the triad for identification of pleural effusion are to look for dynamic findings that are characteristic of pleural effusion.
The diaphragm moves the lung itself flaps, it expands.
It looks like a jellyfish, hence the term jellyfish sign.
If you happen to use M mode, you can find a sinusoid sign and within the effusion there can be movement of particles so-called plankton signs swirling of septations and fronds.
However, the absence of dynamic signs does not completely exclude an effusion.
Here's an example of some dynamic findings consistent with pleural effusion.
But before we list them, we have here the diaphragm, the chest wall, the surface of the lung subtending a relatively echo free space.
And now the dynamic findings are the pleural, sorry, the diaphragm that moves.
And we have a miniaturized lung which flaps, which moves spontaneously with respiratory cycling.
Here's another little bit of it within the effusion.
Here's the interface between the airless or atelectatic lung compressed as it is by the effusion and aerated lung.

Sizes of Pleural Effusions

Effusions come in different sizes.
Here's a small one. We have the diaphragm.
We have a left lower lobe alveolar consolidation pattern with an odd short axis view at mitral valve level of the LV and only a small echo free space.
But once again, it's surrounded by bordered by the visceral pleural surface, the inside of the chest wall and the diaphragm down below.
And there's an element of dynamic movement, a small pleural effusion.

Guiding Thoracentesis and Safe Device Insertion

If one of the main reasons to identify a pleural effusion is to see that it's there.
The second main reason of course in identifying it is if clinically indicated a thoracentesis may then be safely performed.
Therefore, a major application of pleural ultrasonography is to guide safe device insertion anywhere from a small needle to a large bore chest tube.
Obviously the challenge is to find a safe path for needle insertion.
For, in my experience in training a lot of house staff neophyte scanners, the most common errors in this decision as to where to place the needle is that the examiner becomes convinced that the hepatorenal or splenorenal recess is the diaphragm and that the liver or spleen, which are above that recess are echo dense effusions and they plan a access track that leads to catastrophe.
In addition, another common error is that the examiner just isn't sure that there's an effusion.
And again, I wouldn't consider that a major error because caution is always the best defense practice, therefore makes perfect.
Always identify the diaphragm.
Here we have the curvilinear diaphragm.
This would be a scan that's done in longitudinal plane with a 3.5 megahertz cardiac transducer.
The better to fit through the ribs, and this would be in the mid axillary line properly called a coronal plane.
We have here medially if this is the spine with a nice bamboo sign.
These being the disc spaces.
Here we have a medial effusion with a bit of flapping lung there.
Dynamic findings, typical anatomic boundaries, an echo free space.
This is not the diaphragm obviously because the kidney lies below, but in supervising an inexperienced scanner, sometimes it's not so clear.
For example, we start our scan here and someone might think that this is an echo free space and this is sort of like maybe long diaphragms down here set up for the procedure.
But the more careful examiner always looks for the kidney before.
So this would be subdiaphragmatic, this fluid collection With even minimal experience.
This is not an error that's commonly made.
Things get more complicated when there's a hemothorax or pyothorax here.
I would challenge anybody to be sure that this is an effusion.
It's very echo dense hypoechoic.
There are areas within it that are hypoechoic.
There appear to be little white dots that might represent air.
The diaphragm is not easily discerned.
This is a hemothorax with further careful scanning.
The experienced examiner might make the call and proceed with device insertion, but the examiner with standard skill level might wanna back off on this one and say, I'm not completely sure.
Perhaps it's time to define this space with CAT scan because ultrasound is not definitive.
So take care with hyperechoic effusions.
The assignment therefore is simple.
Find the fluid, establish a safe site angle and depth for needle insertion, then proceed with device insertion.
And on occasion, if it's a large device to check for proper device position.
And for those who are interested in safety, of course, any thoracentesis would be followed by a post procedure check for pneumothorax.
Checking for sliding lung.
Here's an example of search for device insertion.
This is a pigtail catheter inserted into a malignant effusion.
It's reassuring to find that it's in proper position.
Of course, we have an echo free space subtended by the inside of the chest wall.
The surface of the lung greatly diminished in size.
The lung is by compressive effect.
The diaphragm is not immediately visible.
We'd have to scan down one or two interspaces, but I wonder whether it has a reverse curvature and very large effusions are found to invert the diaphragm.
And there are some who say that with diaphragmatic inversion, the patient at that moment will become severely dyspneic from the effusion.
We have some dynamic findings.
Obviously movement of the lung, finding the fluid is pretty straightforward.
It's relatively echo free.
It may occasionally be dense and usually a free flowing.
Well always if free flowing.
It seeks a dependent position in the thorax.
Occasionally it's loculated. It'll be any place then.
And for the intensivist, it's very difficult to determine safe site for needle insertion based on supine chest radiography.
There's a summation artifact there, rotated underpenetrated.
You don't know if it's an effusion, an area of consolidation or both, or veil like radio density from soft tissue artifact.
These films are our curse.
However, it is quite feasible for the non radiologist, let's say the intensivist to perform ultrasound guided thoracentesis with a very high level of safety even on patients receiving mechanical ventilatory support.
This is a especially challenging patient population because if the visceral pleura is lacerated, the patient may develop a tension pneumothorax being on a ventilator and become critically ill quite promptly as a result of iatrogenic issue, it becomes very important then for the intensivist to develop a skill, good skill level in identifying a safe site in this patient population here.
This article will reassure you that ultrasound guidance of thoracentesis can be performed with great safety in this challenging patient population by non radiologists.
The identification of the safe site requires that the pleural effusion be seen.
That there be no lung nearby.
That diaphragm is out of the needle track, that there be no other organ nearby of concern.
Once the site is identified and the angle is determined by the angle of the transducer, the skin may be marked by indenting the skin.
The site may be marked by indenting the skin, say with a needle cap.
Some people use indelible ink, but I've always found that that sort of fades out as you wash the skin and what clean the skin.
Once the site is marked and the patient is fully prepped for the thoracentesis, it's very important to check again and the thoracentesis should be performed promptly without any patient movement between scan and needle insertion.
It can be, the needle can be inserted using free hand technique, meaning it does not have to go under real time guidance.
And the needle may be used for simple thoracentesis.
But obviously if there's any interest in a high volume thoracentesis, safety requirement indicates for a catheter insertion.
The key element of success is that the angle of the needle syringe assembly must precisely duplicate the angle of the transducer that was used to establish the safe path for needle insertion.
Therefore, there should be a minimum amount of time between the final scan and needle insertion.
So the operator is a clear visual memory of transducer angle.
After all, they have to duplicate it very precisely.

Techniques for Accessing Effusions in Supine Patients

Free flowing fluid will always seek the most dependent part of the thorax in the outpatient clinic or out on the floors in the hospital.
Patients when they have thoracentesis are seated upright and there's no challenge in finding the effusion.
The scan is done over the posterior back, the diaphragm is identified, et cetera, et cetera.
No big deal. But in the ICU, most of our patients are supine.
So the effusion sinks to dependent position.
Sometimes it's a little hard to get a good angle for access, Especially if it's a smaller effusion.
The bed gets in the way.
You can find it with the probe transducer.
But to get the needle assembly into proper position may be a challenge.
A couple of techniques. One is to sit the patient up and have someone hold the arm ipsilateral arm over the patient's body and then scan the lateral chest.
You can roll the patient over in the lateral decubitus position, slide the patient to the edge of the bed, but whatever you do, assign one person on the team to watch that endotracheal tube.
It's a sad day when attempted thoracentesis results in unplanned tube endotracheal tube removal.
Here we have a larger pleural effusion can be approached in supine patients simply by doing a coronal section here, mid axillary line.
It's a cardiac probe.
They're useful 'cause they have a small footprint that's straightforward.
Here's the semi supine technique with the assistant pulling the patient over, but you had an endotracheal tube in this patient.
A couple of lines in very unstable.
This person has to hold it for 10 or 15 minutes.
This is often impractical in patients who are very, very sick.
To roll the patient over and lateral decubitus is definitely an option.
And then to bring the patient carefully, emphasis carefully to the side of the bed, tying them in with a little sling, the operator can sit on the floor and come up scanning for the smaller effusion.
We call this the garage method as if the garage mechanic is underneath the car looking up.

Pitfalls in Site Selection

There's some pitfalls for site selection.
For example, in the obese patient, the transducer can be pushed into the skin, even several centimeters.
Then the measurement is made for depth.
And then during the thoracentesis, The needle goes into the estimated depth of penetration with no fluid.
This is because skin indentation artifact has occurred, causes underestimation of depth of needle insertion.
Sometimes in patients who are very skinny, the skin can be very mobile.
So the inexperienced operator will traction on the skin, pull it a few centimeters to one side, make the mark and then release the skin and the mark moves to a completely different position.
So it's very important for the operator to hold the skin in neutral position.
Machine magnification can sometimes confuse the inexperienced operator.
They'll think it's much closer or further than it really is.
So they need to attend to that.
The key element of success, therefore to repeat must be that the angle of the needle and syringe assembly must duplicate the angle of the transducer used to establish the safe path for needle insertion, there has to be a minimum amount of time between the last scan and the procedure.
And there could be no patient movement between scan and procedure for fear that the fluid and the position of the lung will change by change of body position.

Small Effusions and Dry Taps

How small is too small?
Well, with a steady hand, if there's greater than 10 millimeters of visceral to parietal distance, it can be done safely.
To enlarge the target area, always scan as dependent as possible and be very careful of the lung sliding into the field.
With respiratory cycling, I'll warrant that this little effusion is too small to tap safely unless with a very, very steady hand.
We'll have a senior fellow or an attending do this one if it really even needs to be done with ultrasonography.
There'll be dry taps.
You see the effusion, but the needle doesn't return fluid.
Number one would be compression artifact that the measurement for distance is underestimated because the edema has resulted in compression artifact.
There just have to go in a little further.
A heavily loculated or septated effusion may block the needle.
The septation is sucked into the needle and just blocks it.
Sometimes some tissue plug as the needle is inserted, gets into the needle.
If the needle is inserted too far in, it may impinge on the visceral pleura and no fluid will be forthcoming.
Further insertion the needle may result in air in the syringe.
The other cause for dry tap is if the patient is moved between the scan and the tap.
And then poor angle selection is an occasional cause.
If possible, it's best to have a final angle of attack that's perpendicular to the skin surface 'cause that's very easy to duplicate with the needle assembly, what's the response scan again, real time guidance is generally not needed, but always watch the house officer very, very carefully.

Loculated and Complex Effusions

A loculated effusion wherever it's found.
The same principles hold.
Here's an example of a complex effusion heavily septated the diaphragm, the chest wall, the surface of the lung.
Dynamic findings rather a hyperechoic element.
Here, this effusion would be typical of a loculated effusion.
This is subpulmonic in location and in scanning this, this is very likely going to require insertion of a larger device followed by thrombolytics, if that's the philosophy of the clinician, or followed, pressed by the necessity for surgical intervention.
If that's the philosophy of the clinician.