"F.A.S.T" Focused Assessment by Sonography in Trauma - SD

Introduction to the FAST Exam

Okay, we're gonna talk about the focused assessment by sonography and trauma exam today. And that's often abbreviated to the FAST exam in English.

The lecture outline, what the lecture's gonna consist of is look at the protocol, what's normal and how does it look, what's abnormal and how does it look, pearls and pitfalls. Okay? And then we'll integrate the whole thing in the trauma evaluation at the end.

Rationale and Protocol

First of all, to look at the rationale and protocol, just remember at the outset, the FAST is looking for evidence of injury. We're not actually looking for the organs that injured themselves. We're looking for indirect evidence, which is gonna be free fluid in abnormal locations.

So there's quite a lot of work been done on this. And as you can see here is a review of 10 of the bigger articles in the English literature at least. And you can see that seven out of the 10 have been done by non-radiologists, by clinicians, either emergency physicians or predominantly surgeons. And you can see that the sensitivity and specificity here kind of runs in the 80 to 90 range for sensitivity and 90 to a hundred range for specificity.

So let's just think about the use of FAST compared to CT. There's gonna be no radiation involved. There's no contrast. It's fairly rapid to perform. It's repeatable. It can be done without taking the patient outta the resuscitation area. It's fairly inexpensive and becoming increasingly inexpensive with technological advances.

We're not gonna get any organ specific information, unlike the CT scan. And retroperitoneal injuries tend to be missed on ultrasound. So be aware of that.

Compared to DPL, which is something that's rarely used now in the United States. But in parts of the world where CT is less available, it's still an option. We're gonna have a non-invasive study. It's going to be rapid, again, probably much faster to do a FAST exam than a DPL. It's repeatable. Unlike the DPL, the cost is relatively low.

This information about the peri and pericardial space is available for the FAST exam, but it's not available in the DPL. And the DPL does give us information about hollow viscus injuries, whereas that's an area that the FAST exam is weak.

Equipment for the FAST Exam

What are we going to use to do the FAST exam? Ideally a small footprint probe, 'cause a lot of the scanning tends to be done between the ribs. So you can actually use this cardiac phased array probe as well. If not a general purpose abdominal probe is used by many people very successfully. You're gonna be running in the two to five megahertz range for a frequency.

Fluid Dynamics in the Peritoneum

Well, let's just think a moment since we're looking for free fluid. What's gonna happen if you get release of free fluid into the abnormal spaces in the peritoneum? And just looking at a sagittal view here, you can see that in this area around L five, the peritoneum's like a watershed in the peritoneal cavity, and anything that bleeds north of this or superior to it is going to flow northwards towards the diaphragm and anything that bleeds and ultimately it's gonna pool right here behind the diaphragm in this space down here.

And conversely, anything that bleeds below this level is going to pool in the pelvis and be identified down here in the pelvis. As you can see, the pelvis is actually a lower spot than the subphrenic areas around the kidneys on either side. But despite that, there's many more sources of bleeding in the upper abdomen. So blood is much calmer in supine patients at the in this area than down in the pelvis.

If we now consider the same concept in a transverse plane, and here we are at the level of the kidneys on a CT scan, you can see that anything that's on the right of the vertebral body is going to pool down between the kidney and the liver down here. And this space around here. And anything on the left is likely to pull in the analogous space between the spleen and the kidney on the patient's left.

Since the spleen and the hilum spleen is actually inside the lesser sac, and this is a fairly tight volume, frequently blood that forms here actually flows across here and is also found in the right upper quadrant in the hepatorenal space. And so you will find oftentimes this a positive free fluid exam in the right upper quadrant, even though the bleeding's the source is the spleen.

Finally, the other space that we will be examining is the pleural space down here, just so that we don't forget it, which is one of the common sources of abnormal free fluid when there's blunt abdominal trauma.

The 10 Potential Spaces in the FAST Exam

So the way to think about this is that there are, although there are four windows, and these are the four which are frequently described here, there are actually 10 spaces that we actually have to evaluate when we're assessing these patients. And it's really the 10 potential spaces that are really the focus of our inquiry and our examination.

So in the right upper quadrant, there are four in the subxiphoid region, there's one in the left upper quadrant region, there's another four, in fact, the same analogous four in region one. And finally in the suprapubic region, there'll be one space that adds up to 10.

Let's go through the potential space. In the right upper quadrant going from the top, they're going to be pleural, subphrenic, hepatorenal, which is also known as Morrison's and infrarenal. The one space that we're gonna examine the subxiphoid region is the pericardial space. The left upper quadrant is the same four spaces as there were in the right upper quadrant, pleural, subphrenic, splenorenal on this side, and infrarenal finally, in the suprapubic region, we're going to look at one space, which is this rectovesical space, or pouch of Douglas, depending on whether you're looking in a man or a woman respectively.

Normal FAST Exam

Right Upper Quadrant

So let's just consider now what does a normal FAST exam look like? And what is the appearance of normal? So studying in the first region, the right upper quadrant, usually you're going to be have to put your probe intercostal. You might try putting it subcostal here in the midclavicular line, and using the liver as a sonographic window.

If you have a cooperative patient and many trauma patients obviously not able to be cooperative, you can ask the patient to take slow, deep breaths to bring the liver down to help you provide a sonographic window. If you use the intercostal spaces, which is by far the majority of cases, you will need to do that, you can try and angle the probe parallel with the ribs, which in shorthand we say 10 o'clock, the patient's head's at 12 o'clock. The probe pointer is gonna be up in this upward rightward direction here.

So the four spaces that you can look for here, and you can see them in this image are, first of all, the pleural space. Again, going from the top. This is the patient's head, the patient's feet, the pleural space, and this is the diaphragm, this bright white line here, the subphrenic space, which is on the other side of the bright white line of the diaphragm, the hepatorenal space, which is Morrison's, which actually in this patient goes almost all the way around the kidney. And then finally, we want to check the inferior pole of the kidney here for blood tracking up along the colic gutter. They're really seen on a single view, as in this case. And we usually have to image them separately.

So first of all, considering the pleural space, the key finding here is to identify mirror artifact right here. The presence of the mirror artifact is actually caused by the intensely echogenic diaphragm, which provides a very good specular reflector. It gives the appearance of liver on the other side of the diaphragm. If that's absent, if you get black back here instead of the appearance of liver, then you should be suspicious that you've got free fluid in the pleural space. And in the context of trauma, that would usually be a hemothorax.

The subphrenic space is just on the other side of the diaphragm. Occasionally we see free fluid here, and once your eyes trained on the diaphragm, you may as well check for it while you're reviewing this spot.

Next to get to Morrison's pouch, which is in terms of intraabdominal free fluid, the most common site to identify it on the FAST exam, in transverse view, this is a view of the kidney right here, liver diaphragm again, and this will be Morrison's pouch in the sagittal longitudinal view. This right here is Morrison's pouch.

While we're looking for free fluid, finally check the inferior pole of the kidney, which is nicely seen in this patient right here without even having to move the probe.

This is a live clip of a FAST exam. You can see first all imaging the Morrison's pouch right here. And then there are nice images of the diaphragm here, with above the diaphragm. The mirror artifact, easily seen right in here. This is the rib shadows here are somewhat distracting. And in this exam, a better quality exam would've been obtained if the examiner had managed to make the probe angled more parallel with the ribs.

Pericardial Space (Subxiphoid Region)

Moving on now to the second region, the pericardial space, most commonly we use the subxiphoid window for this, and the probe needs to be placed immediately below the xiphoid. And oftentimes you actually place the probe on the chest to just slide it down over the xiphoid. You need hepatic window to identify the heart.

So again, if a cooperative patient can help you out, you can ask 'em to take a deep breath and hold a deep breath and hold, or just take steady deep breaths. You want to aim the probe towards the patient's left shoulder up in this direction here. And a mistake is frequently made, is that people forget that the heart and the mediastinum are immediately right behind the sternum. So you have to keep this probe pretty much parallel with the sternum and depress the whole probe to get underneath the xiphoid process here to get your images.

Okay, the points are in this view is going to be over to the patients right here, at nine o'clock using the previously described shorthand. So when you get the probe in this position here, again, pointer over here towards the patient's, right? You're gonna get an image like this with the right ventricle closest to the probe left ventricle behind it. You can see this white line of the septum here, and then the right atrium and left atrium relating to those two.

Here's a clip showing the same thing right here. And you can see right here, right ventricle, left ventricle septum right here. You're actually catching a little bit of the aortic valve right here and not seeing the left atrium so well. And here's the right atrium back here with a tricuspid valve between the space that we're really interested here that we're interrogating is the pericardial space, which is signaled by this bright white line, and also back here as well. So this white line will be separated by black in cases when you have pericardial fluid.

Now, some people advocate turning the probe to 12 o'clock, turning the probe so that it's points towards the patient's head. For the subxiphoid view, it gives it also gives a view of the inferior vena cava, and it gives the pericardium adjacent to the liver and the diaphragm, on that view, technically it's oftentimes a little bit more difficult because it's even harder to get the probe under the patient's xiphoid and behind the sternum when it's oriented in this direction. But this is what the view looks like. Here's the inferior vena cava. Here's the liver right here, the diaphragm. And this is the heart right in here. And this is the image that you're going to get on this view if you're unable to obtain images from the subxiphoid view, which might be the case if you have abdominal injuries wounds, or if you a very protruded abdomen, then use parasternal views as needed.

Left Upper Quadrant

So moving on to the third region here, we're getting to the left upper quadrant. Now, this is technically the most challenging view. You're gonna angle the probe parallel to the ribs. Again, usually this is going to be on this side. It's going to be towards the head of the ribs and the two o'clock position.

As a general sort of pearl here, the position that the probe will be placed in is going to be more posterior and more cephalad more towards the patient's head than most clinicians expect. If you're too far inferior, you're not going to be able to image the structures because there's going to be the descending colon the way, and that's all you're going to be able to see.

So again, to obtain the images of the various structures, you often need to go through up and down through several rib spaces. And you can see here again, how the probe's kind of angle parallel to the ribs.

So the potential spaces we mentioned before are four, starting at the top, on the above the diaphragm, there's gonna be the pleural space. And the absence of fluid here is gonna be signaled by the same mirror artifact we saw on the right below the diaphragm is the spleen, and there's the spleen, splenophrenic space here. The subphrenic space is also a potential space for free fluid. Below that, the kidney and the space between those, the splenorenal space. And then finally, the inferior pole of the kidney should be checked again for free fluid coming up the left colic gutter or pooling down here behind the kidney, the psoas muscle is frequently seen as in this case, and should not be confused with free fluid.

Here is a clip of the left upper quadrant exam, little on the dark side. Again, we're having rib artifacts frequently coming across the images here. Here's the diaphragm back here is the spleen right here. And here's the spleen space with some perinephric fat with internal echoes, which distinguishes it from blood. And every now and then we get an image here above the diaphragm of mirror artifact. Which on this image might be a little hard to see because at least it's in this particular version it seems to be projecting a little bit dark.

Suprapubic Region

So finally, moving on to the fourth region that we're gonna examine. We're gonna look at the suprapubic space. And in the male, it's going to be, we're looking retrovesical, the rectovesical, sorry, space. And in the female, the rectouterine space. And the female will also be looking at the vesicouterine space anterior to the uterus as well. Sometimes you see free fluid there. The rectouterine space is known as the pouch of Douglas, and frequently referred to as that in women.

So you're gonna put the probe immediately above the pubic symphysis. It's like the xiphoid here. You kind of want to put the probe on the bone and then just slide over it. Because you get the most use out of the bladder window if it's available. If you have your probe placed as inferior as possible, you can actually make use of a very small bladder in that case, as you can see here, the probe is in the transverse plane is oriented towards the patient's, right, the nine o'clock view, you're going to start with your probe angled quarterly, down into the pelvis here. And then you're going to steadily scan superiorly by fanning the probe your hand back in this direction. So the probe fans superiorly, in the male through the seminal vesicles in the female around the level of the cervix.

The we'll talk about one of the pitfalls of this exam in a moment. And then you're going to scan north to the dome of the bladder. You want to scan before the Foley's placed. And if there's an urgency to placing the Foley, the usual order of the FAST exam can be changed to do the suprapubic scan before the Foley's placed, because the bladder is important window to identify fluid.

The primary view here is transverse, sagittal and parasagittal longitudinal views can also be helpful, especially with any question about what you're looking at. You want to systematically scan from inferior to posterior We've mentioned, and free fluid may be seen either behind, above, or anterior to the bladder in any of those places.

So the normal view in the male, this is the transverse view in the male. And back here, you're seeing seminal vesicles. This is the sagittal view in the male. His prostate and seminal vesicles are on either side of the scanning plane, so they're not seen in this midline, sagittal view. This is the bladder here, providing the window in the female. This level, you can see the uterus right here. And behind that, this echogenic structure is the rectum. And you're gonna be looking for fluid on either side. Here in little triangles is the earliest sign of free fluid in the pelvis. And the female, this is the longitudinal view in the female pelvis. Here is the bladder. The vaginal stripe can be seen right here. It's usually characteristically echogenic line between two hypoechoic structures, which are the vaginal walls. And then the cervix is actually down here in this patient. And free fluid will be down here, and oftentimes runs up here along posterior to the cervix. And the body the uterus right here, this is the patient's bladder is fairly empty. And obviously some women have retroflexed uterus, which will not show up on this scan.

This is a transverse clip of the suprapubic exam in the male, the beginning of the clip we see. And we're just about to get back to it, to run it one more time. Beginning of the clip here is the prostate, scanning superiorly. We get to the seminal vesicles, which become symmetrical structures on both sides of the bladder. And finally, we're gonna scan to the dome of the bladder and see no free fluid back in this area.

Abnormal Findings in the FAST Exam

Moving on now to assess abnormal findings in the FAST exam, and we'll go through the same order again, just to discuss each one in turn.

Right Upper Quadrant

So, first of all, looking at the first region we've discussed in the right upper quadrant, which is the pleural space, once again, we're looking for mirror artifacts. And this these two stills demonstrate the loss of mirror artifact in this characteristic pointy shape down here, and a larger one right here, which represents hemothorax. This is a small, very small hemothorax. And here's the larger one. This is the edge of the lung coming down. You can see after the lung becomes contiguous with the diaphragm up here, you once again have the mirror artifact, okay, that we talked about before. So here we have hemothorax right here. Here we can see liver with diaphragm right here. And above that, this pointy area of dark fluid, which does not show mirror artifact.

Okie doke. Alright, so moving on here. This is the next spaces we're going to look at. We'll skip over the subphrenic space. We do have an image of subphrenic fluid coming up. But the most common site for finding free fluid in a positive FAST exam is in Morrison's pouch, which is the hepatorenal space. Here is an image of hepatorenal fluid. Here's the kidney, the liver, And this is a sagittal view, and transverse. Once again, this is a small amount of free fluid, but any free fluid should be identified in this area. 'cause it's usually pathological significance, diaphragm, liver, once again, and transverse view of the kidney.

Now here, this here is not free fluid. This is bowel, which is usually gonna be more obvious in real time because you'll see it peristalsis. But you can see the plica circularis characteristic of small bowel right here.

Here's a clip in the transverse view, predominantly showing nice mirror artifact back here, diaphragm, liver and gallbladder up here. But between this transverse view of the kidney and the liver, you can see this strip of dark free fluid right in here, which represents intraabdominal intraperitoneal hemorrhage.

Pericardial Space (Subxiphoid Region)

Now moving on to the next region, region number two, which is looking for the subxiphoid space. This clip shows the subxiphoid four chamber view we discussed, and here is nicely seen a rind here, free fluid, hemopericardium, which is seen anteriorly to the heart and also posteriorly back here. And it's pretty much circumferential. There's an area here adjacent to the right atrium, where the free fluid is not so well seen. And this, it's thicker and thinner in various hearts, but it's pretty much circumferential free fluid.

The classification of pericardial fluid collections, traditionally by cardiologists has been really a little bit arcane. They've categorized as physiological, small, moderate, large, very large, and tamponade. Each of those has defined measurements. And needless to say, for clinicians in practice, such classifications are hard to keep in mind and keep straight, especially in the heat of a trauma evaluation.

So really, it's easier in the setting of trauma, where this even smaller effusion might be very significant if it wasn't there 15 minutes ago before the patient had any trauma. And if it's accumulating at 20 or 30 ccs a minute, and then by the time it, it'll only take five minutes to reach a critical volume of a hundred to 150 ccs. We really just need to think of two different kinds of effusions in trauma. One is effusions that are unrelated to trauma. They're usually small. They're often adjacent to the right atrium, and clinical acumen. And we will, a clinical acumen we need will be needed to sort this out.

Conversely, if they are related to trauma, any size can rapidly expand, as we've mentioned. And the risk of tamponade can occur with any circumferential effusion. So the one we just looked at, if it's acute, we put the patient at risk for rapidly expanding and causing tamponade. So if unsure whether the effusion you're looking at is clinically acute or not, perform serial exams, that's really the key to this.

Again, most of the time a patient will be suggesting that they have a problem by the hemodynamic status, because tamponade in someone who's had an otherwise normal pericardium up to that point, occurs very rapidly.

This is a case with a pretty massive traumatic effusion. You can see this atrial collapse here in diastole. We're not really seeing ventricular collapse, which is a much more specific sign for this, since atrial collapse can happen with hypovolemia and various other conditions as well. But with an effusion this large in the setting of trauma, you'd be very concerned for impending tamponade, and act accordingly.

Left Upper Quadrant

Moving now to the left upper quadrant, there's going to be, as we've mentioned, four potential spaces where we can see fluid. The commonest one is going to be in the splenorenal space. And the second most common is going to be in the pleural space, signaling hemothorax, once again, diaphragm spleen potential space here with pointy black fluid. And here we have spleen diaphragm, above it. And here we can see the lung outline by hemothorax right here.

Here's a clip showing, it's a fairly subtle free fluid, but you can see it above and below the spleen right here. And also spreading around here. We'll discuss this clip a little bit more extensively later. But this actually is fluid filled stomach, not kidney. But nevertheless, outside that you can see pointy collections of free fluid extending around the spleen, both under the diaphragm and up in this direction right here. There's also pretty extensive clot here. And again, the inexperienced eye, this clot might just have the same density of soft tissue, but actually with experience can be distinguished and recognized as such.

This is another positive left upper quadrant exam. Again, a little bit of free fluid just hanging out here. The superior pole of the spleen. And maybe just creeping up a little bit here in the splenorenal space. Here we can see the shadowing caused by the lung. And you can see how technically this view can be quite difficult because the spleen gives you much smaller window than the liver does on the other side. So it's hard to get in to get a view of this. But this is a positive FAST exam in the left upper quadrant.

Suprapubic Region

Moving on to the suprapubic region. Here's the bladder, and this is free fluid posterior to the bladder right here. Small amounts before the rectum gets pushed away from the bladder by the free fluid here. Small amounts appear as triangles on either side here, and that's often referred to as a bow tie sign. This is a sagittal view. This here is actually the prostate and caught the seminal vesicles. So this is actually not truly sagittal. This is a parasagittal longitudinal view, but this here is free fluid back here. Again, the appearance of free fluid is much clearer when you look in real time.

This is a transverse view of the bladder and the female. This is the uterus here. We just scan up through the bladder. And all through the space up here, we're seeing free fluid floating around the bowel right here. This is bladder, the dome of the bladder, and once again, lots of free fluid back here, posterior to the uterus, which is right here and in between the loops of bowel.

Pearls and Pitfalls of the FAST Exam

Okay, let's just think about some of the pearls and pitfalls of the FAST exam. Starting again, just running through the four regions to keep this theme going.

Patient Positioning and Right Upper Quadrant Pearls

Patient positioning does make a difference, especially for fluid in the right upper quadrant, and that's been demonstrated in a couple different ways. Actually, Dr. Goldberg, in one of the earliest studies on this subject, using cadavers and peritoneal dialysis models, showed that he could reliably identify as little as a hundred ccs, by putting the patient in the right side down decubitus position, which is something that we rarely actually doing the trauma evaluation, but is maybe something we should consider doing. And certainly if the patient's being turned to examine their spine when they turn onto their right side, it might be an opportunity if a sonographer is available to examine Morrison's pouch to get a better look at that space.

In terms of Trendelenburg positioning, a study was done in 1999 by Dr. Abrams, and she actually showed that using a DPL model, a model of patients receiving DPL, that she could reliably identify volume of 440 ccs of free fluid infused from the DPL versus about 50% more when the patient was supine without any Trendelenburg.

So, again, this is actually a real case patient had a question of free fluid here in Morrison's pouch. You can just see a very subtle black line between these two echogenic fascial planes here. And the patient was put in Trendelenburg, and lo and behold, the free fluid got larger and we were able to diagnose the hemoperitoneum earlier that way and expedite the patient's care.

Another pitfall of scanning the right upper quadrant plane is that people often have a tendency to scan right down at the bed here on the right side. And the problem with that is that if you have free fluid pooling back here and you're scanning too low down, then your probe and your imaging plane might actually go across here and be superior to the collection of free fluid.

There's a couple of things that you can do to avoid this. First of all, consider scanning. Or just as a matter of course, whenever you scan, you should scan the whole space. Don't just get one image of the liver and kidney. You'll hear this a repeated theme in this lecture, but the power of bedside ultrasonography in the hands clinicians, is that we can do this in real time. And one of the good habits that we need to develop is that we scan through all the tissue planes of the organs or the areas that we're interested in.

So systematic real time scanning through tissue planes might will save you this, if you go through the whole area, the whole hepatorenal region, as well as the pleural regions and the other regions you evaluate in the FAST exam.

Secondly, try to put your probe as anterior as possible. It is slightly counterintuitive 'cause it actually moves your probe away from the area where the free fluid is gonna be. And people feel that they should be as close as possible to it to see it, but you get a better view down here. And since fluid is going to be pooling down here by being up here, you are actually looking down at the dependent areas when someone's supine on a stretcher.

Thirdly, you might want to consider using the transverse plane, the transverse plane in as opposed to the longitudinal plane is going to catch everything that's more posterior because it's at right angles to this entire potential space back here. And this is once again of the view we already seen of a transverse of the kidney. You can tell by the shape of the kidney here, with a small amount of free fluid here and the liver around it.

So this is a transverse view or a small amount of fluid that if the probe had missed this in a longitudinal plane might easily have overlooked this area of free fluid here.

Pleural Evaluation

So what about the evaluation of the pleura by the right upper quadrant? And likewise for the left upper quadrant, how sensitive is the FAST exam for hemothorax? So in 1997, one study of this showed sensitivity of 96% specificity of a hundred percent, essentially identical to that a chest x-ray. I think this is probably it was a small study, but it's probably pretty accurate. People who've done quite a bit of scanning know that they can see really minuscule amounts of fluid in the pleural space, especially if one scans the whole way through the pleural space. And great views are available through the liver. So very small volumes of fluid are identifiable, whether they be hemothorax or pleural effusion.

The sensitivity seen in this earlier study by Rozycki showed a lower sensitivity, but many of the false negatives were because people actually said they forgot to look. And then others because the hemothorax was delayed in presentation, which obviously is something that the ultrasound is never gonna be able to predict the development of a hemothorax after the ultrasound.

The differentiation of pleural effusion from hemothorax is similar to the differentiation of ascites from hemoperitoneum, and we'll talk a little about that coming up in the subxiphoid view.

Subxiphoid Pearls and Pitfalls

One of the pitfalls or things to watch out for a prot abdomen is obviously going to be an impediment to doing this exam as our abdominal wall in injury and tenderness. The one of the other things that is frequently overlooked is that in a subxiphoid view, the depth required to see the posterior wall or the pericardial sac is much greater than is commonly used in the right upper quadrant. So don't forget to adjust your depth and gain settings when you do your subxiphoid exam.

One of the pitfalls is the pleural fluid can be mistaken for pericardial fluid and vice versa. Pericardial fluid, of course, should conform with the shape of the heart and be around it, and pleural fluid does not do that.

And just one thing to add here again, in terms of the patient technical obstacles to this part of the exam, familiarity with the parasternal views and the anterior chest wall views of the heart really help clinicians out when it's hard to scan the subxiphoid window. So that skill is something that's very useful to develop to be comfortable with the FAST exam.

Left Upper Quadrant Pearls and Pitfalls

Looking at the left upper quadrant, once again to remind you that we're not likely to see parenchymal or organ injury with a FAST exam. So don't expect to see badly injured or damaged spleens unless you're seeing free fluid that accumulated as a result of that.

This here actually is an example of a subcapsular hematoma that was identified in ultrasound. But again, this one was an experienced sonographer or might not realize that the key point for the introductory FAST lecture is that you can see free fluid back here running from the spleen into the splenorenal space here. Here's the kidney. And maybe a little bit even more anteriorly up through here. This white area here is actually clotted subcapsular hematoma. But might have been mistaken for soft tissue with if someone were less experienced at this exam.

Pitfalls in the left upper quadrant, the splenic hilum and the fluid filled stomach can both sometimes until they've been until their sonographer is familiar with these can sometimes cause confusion. Here is the case of the splenic hilum, the vessels of the splenic hilum, sometimes quite prominent. And this actually this particular cut makes this vessel appear like it's pointy and spiculated like free fluid. In fact, it's not, it's a negative exam.

And here is someone who came into the trauma bay after partaking of some volume of beer. And this is a stomach full of free fluid. You can actually see the bubbles rising in the beer here. And this is the head which is causing this comet tail artifact from the bubbles that is coming down from this area here. Again, contrary to free fluid, this is round the appearance that usually allows you to recognize its stomach and its contents right here.

We have a fluid filled stomach coming in right here, spleen, kidney. But back here you see this area of stomach, which is definitely a fluid filled structure, but unlike fluid, it's kind of round state in shape, well contained. And you can kind of see the rugae of the stomach again with maybe some artifact caused by gas swallowed gas mixed in with the contents the stomach. But the first time this is seen, it can sometimes give people some problems and recognizing it what it is.

Suprapubic Pearls and Pitfalls

Moving on to the suprapubic view, the biggest pitfall here is that after scanning the rest of the abdomen, you really have to turn your gain settings down. The bladder is a fantastic sonographic window. And as a result, you get intense through transmission of ultrasound waves behind the bladder, also known as posterior acoustic enhancement. And as a result, the entire area back here gets filled with gain artifact and free fluid, which should appear black is actually blown out by it. And it can be a failure to recognize it, so adjust your gain when you get in suprapubic area.

Occasionally one sees very prominent especially in young, healthy patients who are susceptible to trauma prominent psoas muscles here. And they have an appearance almost of fluid surrounding clot. And again, until you've seen them well might not be familiar with them, they we have the tendons within the mass of the muscle surrounded by the muscle tissue here. And oftentimes they're described as looking a little bit like kidneys with the renal hilum, obviously, they're not kidneys because of the location of the probe.

Seminal vesicles when the gain settings are correct also can be of course, a source of confusion because they appear bilaterally, posterior to the bladder in the area where the bow ties are seen for the early hemoperitoneum in the pelvis. And here's the prostate scanning superior to the bladder. Here are the seminal vesicles spreading apart, but again, contrary to free fluid, you can see these are round very symmetrical and exactly the right place.

As we mentioned before, free fluid is going to be sort just superior to the seminal vesicles. So when you're looking at the seminal vesicles, you're a little bit too far inferior in the pelvis. You're below the pelvic reflection, so you're not likely to see fluid there. This is a diagram indicating that, again, reminding you of this is the bladder. Here are the seminal vesicles. The peritoneal reflection back here is superior to the seminal vesicles. So if you're scanning through the seminal vesicles, you're actually below the reflection of the peritoneum, and you're not gonna see free fluid in the pelvis as a result of that 'cause you're below where the free fluid can gather.

Recommended Scanning Order and Technique

So what order do we recommend that you scan when you do your FAST exam? Everyone has a preference. I find it's best to go in a big clockwise order unless you have any reason to suspect that there's hemopericardium, in which case that can be the thing that can kill the patient most rapidly. In that case, I would suggest you look at the pericardium first, but otherwise, the vast majority of positive FAST exams that's going to be free fluid in the right upper quadrant. So that's probably the place that's worth checking at the beginning.

And after that, it's easy to just take a nice systematic sweep from the right upper quadrant, the subxiphoid region, the left upper quadrant, and then suprapubic area.

So in terms of sound technique, again, complete your exam of each region before moving on. You gotta stay systematic here. There are enough things happening in the trauma bay that if you lose track of where you are, you're gonna overlook things and miss them. So complete each region that we've discussed and complete an exam of each potential space in each region before moving on. So make sure you get all four in the right upper quadrant. A good look at the anterior posterior pericardium and the subxiphoid or four in the left upper quadrant, and then a good look in the retrovesicular space or the retro uterine space.

In turn, the order of the potential spaces within each region really doesn't matter. Oftentimes, you put your probe down, you find you've got a great view of the spleen or the hepatorenal space, interrogate the space completely from side to side or from top to bottom, and then look at the other potential spaces in that region.

If you obtaining still images for QA, do so in a separate sweep because if you're operating machine and freezing and recording images it interrupts your ability to do systematic scanning. And the once again, the power of this device really to give you a really thorough exam in trauma is in its real time scanning through all the tissue planes.

So again, in kind of a summary of technique, avoid the temptation to rush the FAST exam. When you get accomplished at it, you'll probably be able to do a good FAST exam for most patients in 45 seconds. But during the time when you're on the learning curve, a thorough FAST exam will take you a little bit longer. But the value of it obviously will far exceed a more rushed exam in which you overlook free fluid.

There's a nice article written in the journal Trauma by Dr. Biffle, in which she called FAST should Be Slow, which stands for systematic look for occult hemorrhage, which really is systematic methodical scanning in real time, maintain your peripheral vision. Like when you look at a chest x-ray, notice around the edges of your image and always be on the lookout for dark areas on your scan. The token free fluid.

Don't forget, once again, this thing should be thought of as a handheld CT scanner and should be as methodical as a CT scanner is with its gantry. So that the systematic real time scanning through all tissue planes, the again, there obviously are organs and sites in the peritoneum and chest where the free fluid is expected in the vessels, the gallbladder, et cetera.

The key is that free fluid compared to physiologic fluid tends to be pointy. Again, his kidney liver here is a pointy area of fluid in Morrison's pouch. Free fluid slips between the loops of bowel and viscera and any other structures and tends to create these pointy shapes.

And conversely, if you look at this free fluid, which is hanging out, or this fluid rather, this fluid fill structure that's hanging out under the liver, you can see it's rounding in quality. And if you scan through it, you realize that it was limited in rounding all directions. And we recognize that for the gallbladder. Conversely, again, here's the bladder. You can see the rounding shape of the bladder, and either side here, these two pointy triangles of fluid in front of the uterus here. This actually is free fluid, abnormal free fluid, and a positive FAST exam.

Ascites tends to be more sonolucent than blood, and usually could be recognized in the clinical context. Patients with liver disease obviously often coming with skin findings consistent with that, they're often in an older age group, and oftentimes they have findings in the liver with evidence of cirrhosis that are consistent with that. This is very clear fluid surrounding many loops of bowel here. This is ascites.

Clotted blood is something that, again, until you've seen it a few times, can be the cause of false negative FAST exam because it actually has soft tissue density and fresh blood starts to clot within minutes. And I'll show you an example of that coming up. Clot can be hyperechoic and often has sort of a poorly defined mottled appearance, which again, to the inexperienced eye might not look dissimilar from bowel and bowel contents. It's gonna be 12 hours to two days before the clot fibrinolysis and becomes lucent.

This actually is an example of a patient who was pedestrian struck right outside the hospital. He came in within minutes of being struck and had this FAST exam done within minutes of his arrival, probably within 10 minutes of the original accident. He was near arrest with no blood pressure and no pulses, but on ultrasound had hyperdynamic heart identifiable here, surrounded by this pericardium full of completely clotted blood, again, within minutes of the accident.

This patient received a open thoracotomy in the ED. The clot was removed, vital signs returned. He was taken to the OR where his cardiac injury was repaired. And he walked outta the hospital with full neurological function less than two weeks later. So this was definitely a case where the FAST exam helped us to save critically ill person.

Here's a clip showing clotted blood in the pelvis. Here's a large clot right here surrounded by areas of non-clotted or fibrinolyzed blood. And this is this, we've just gone sagittal on the image at the end there. And you'll be able to see when we the sagittal view, if I pause it right here, you can see the bladder, the dome of the bladder right here, and you can see the clot in the blood going anterior to it. So remember I mentioned to you that clot in the pelvis can be posterior to the bladder, above the bladder, or in front of the bladder, or all three.

Perinephric fat is something that can easily be confused with free fluid, or it's usually not dark, but as we've said, so it shouldn't be mistaken for free fluid, but it can be mistaken for clotted blood as we've we just saw a couple examples of clot and they're frequently hyperechoic. Perinephric fat tends to be fairly homogeneously surrounding the kidneys. Although occasionally it could be pointy as in this case here.

The in order to reassure yourself that it is perinephric fat, you should make sure that this is consistent with the patient's body habitus. You don't usually see this on patients that have an asthenic habitus. Number one. Number two, both sides should be pretty much symmetrical. People don't tend to develop perinephric fat on one side and not the other. And if you really have any question, you can roll the patient on one side, and if it's free fluid, it's going to either drain or increase depending on where that patient that side is up or down. Whereas perinephric fat won't change.

Perinephric fat also has these internal echoes which kind of have a signature, which is different from that homogeneous signature of the clot that we saw in the previous two slides.

False Negatives and Positives in the FAST Exam

So what are the likely causes of false negative FAST exams? And I went through 10 peer reviewed articles, the 10 that we discussed at the very beginning of the lecture, and looked at all the cases that they in which they acknowledged that they'd had a false negative FAST exam, that there were almost 6,000 patients in the 10 articles. They had 98 clinically significant false negative FAST exams reported.

And by clinically significant, we're going to find that as something that needed operative repair. A third of those are hollow viscus injuries, which is the type of injury that tends to be missed also by CT scan. And may or may not be picked up by DPL, but it's definitely in all imaging modalities and diagnostic modalities available in trauma. This is the type of injury that tends to be most easily overlooked.

23% or a quarter were splenic, 14% were liver lacerations or injuries. And 11% were diaphragmatic, 10% were hems. The majority of them evolved more than 24 hours after injury. So they probably were not really true negatives in the sense that they were, the FAST exam was accurate at the time it was done, and many were clinically identifiable, so the patients became unstable. And in other cases, repeat ultrasounds revealed the diagnosis.

So using the strictest criteria, as we mentioned, the sensitivity is going between 80, 90%, but using clinical acumen and repeat exams, and probably the sensitivity or the likelihood of false negative studies is much lower than 10 to 20%.

False positive exams are going to be caused by ascites and pleural effusions, retroperitoneal and pelvic hematomas may masquerade as positive FAST exams, although clinically obviously we want to know about them anyway. So that wouldn't be a false positive that was bad for us to know about or the patient to have us know about. Again, false positives will often be accompanied by clinical findings that corroborate them.

Repeat FAST Exams and Volume Detection

When when should you consider doing repeat FAST exams. Really you can repeat FAST exams as often as you want, and as you become more facile at them, the downside of repeating the exam becomes less and less because you're going to spend less and less time invested in doing it.

If you have a stable patient with an initially negative FAST that you want to send home without any further studies, you might consider observing them for six hours and if they're stable, repeating the FAST exam. There's a couple of studies have looked at this. In Porter out of 105 patients with negative repeat FAST, he found that none of them needed laparotomy. And he also found that the positive repeat FAST that was positive led to laparotomy in 40% of patients. Obviously still some of those people were just having sympathetic peritonitis effusions or pleural effusions from contusions or non-operative internal organ injuries that didn't require operative repair.

And Glaser also found that the repeat FAST exam was useful in the setting of delayed splenic rupture, people who were being followed conservatively.

So this is a case in which we actually got a repeat exam, although it was initially the patient was had a clear sensorium and tachycardia, but normal blood pressure and a negative left upper quadrant exam. Patient subsequently became diaphoretic, restless blood pressure dropped heart rate went up, and this extremely abnormal left upper quadrant exam that we've seen once before this lecture was obtained, which really showed clotted blood all through the left upper quadrant with, there's difficulty making out any recognizable anatomic structures in this view.

How much volume are we going to be able to pick up or have small a volume of free fluid in the FAST exam? We've mentioned the Goldberg study of 1970. In 1990, Tyan did a study of volumes, and he estimated that a five millimeter stripe, a five millimeter stripe in Morrison's pouch represented 500 ccs of free fluid. And Branney determined that only 50% of his patients had identifiable free fluid in Morrison pouch after 600 ccs. But 97% were positive after a thousand ccs.

So again, there's some range of numbers in the literature. Probably the bottom line is that between 500 and a thousand ccs of free fluid should be clearly identifiable without, and if there's any question in your mind, repeat scans, put the patient in Trendelenburg, put the patient on their right side could all be things that would help you figure out if you are looking at a small amount of free fluid or not.

It's also true that the larger the volume of free fluid identified, the more likely the patient has need for the OR. So that's also something that if you're in a hospital where you're calling a surgeon, then the your sense of how thick the stripe is in Morrison's pouch elsewhere really has prognostic significance in terms of the care the patient needs surgically.

Other Issues in the FAST Exam

There's several other issues in the FAST exam which we're not gonna cover in this lecture. The pneumothorax evaluation for pneumothorax, which is widely performed nowadays, probably or definitely in our experience more accurate than the chest x-ray, but less accurate than the CT. How many of those are clinically significant is disputed, the FAST exam in pediatrics, the FAST exam in penetrating trauma. This talk is primarily focused on blunt trauma to the torso, specific organ injuries. Some investigators have reported success in assessing this with the FAST and training issues.

Integration of the FAST Exam into Trauma Evaluation

So let's just think about how the FAST exam now is gonna be integrated with the rest of the trauma evaluation. First of all, we're gonna do it after the primary survey. So if the patient is shock, you can do it with a concurrent with a C of ABC when you're evaluating circulation. Otherwise, you do it concurrent with the D evaluation for disability.

If possible, do it prior to the insertion of the Foley. That's less of an issue now than it used to be when the standard of care was to put Foleys in the majority of trauma patients regardless. Nowadays, that's definitely no longer the practice.

And if you're unsure about what you're seeing, repeat the FAST exam in 15 minutes or less and observe the clinical, the patient's clinical status.

So when you've when you do the FAST exam, you want to come away from the bedside with one of the three your three categories in your head to either report to the surgeon or to determine your own steps as the treating physician yourself. Either the first exam is positive for free fluid, yes, it's a positive exam, or no, it's a negative exam. And finally, since we're all clinicians and we know that diagnostic tests work this way, the third category is, I don't know, and obviously it's very important for us to acknowledge when we don't know something, and it's far more useful than being falsely positive or falsely negative. So an indeterminate exam is also a result that you have to acknowledge.

You're gonna combine whichever these things, whichever these categories the patient falls into with the clinical condition. And that's gonna determine the next step, which is either the OR stat or further diagnostic studies, or neither, which will be clinical management.

So, putting this all together, if you are looking at a hemodynamically unstable patient, it's come into your trauma bay, and you have a positive FAST exam, then you should, that patient should be taken to the OR for laparotomy, pretty much.

If the FAST exam is negative, then peritoneal hemorrhage and hemothorax and hemopericardium are probably not the cause. So if you're still concerned about that, you're gonna repeat the ultrasound in five minutes or do a DPL, but most likely there's something else involved, like massive pelvic hemorrhage, retroperitoneal hemorrhage, long bone fracture in the thigh, which can cause the loss of liters of blood and cause hemodynamic instability.

Finally, if you don't know, then you're gonna repeat the outstanding in five minutes and or do DPL and or go to the operating room. Obviously, you're not gonna usually stand hemodynamically unstable patient the CAT scanner for further studies over there, because that's frequently a recipe for disaster.

If you have a hemodynamically stable patient that's coming to trauma bay and it's lying on the gurney in front of you and you FAST is positive for free fluid or fluid elsewhere, then you probably have the luxury of getting more definitive imaging studies to tell you the location and the and some organ specific information about the trauma. Most commonly in the United States where CTs readily available, that will be CT, but elsewhere if CTs not available, that might require laparotomy or it might require DPL or further clinical serial observations.

If the FAST is negative. If you have a high clinical suspicion, then you can certainly get further imaging studies with a hemodynamically stable patient. If you have a low clinical suspicion, then you can manage clinically, you can either observe the patient and or discharge them from either the trauma bay or your emergency department.

Finally, if the FAST is indeterminate, again, if you have a high clinical suspicion, get further studies, CT or any other that's available and with low clinical suspicion, repeat the FAST or if you have this available and the luxury of doing this, obtain a CT scan to confirm your impressions.

Questions and Comments

Okay. If there are any questions or comments, I'm available to answer them through the website, which is written on the slide.