POCUS Lung Ultrasound: A Guide to Bedside Lung Imaging

[00:00:00]Hi, I'm Dr. John Kugler with the  Stanford 25 ultrasound series.

[00:00:04]Today, we're going to be learning about  lung ultrasound. Now, lung ultrasound is really important, especially in my practice as a  hospitalist. I use lung ultrasound all the time to evaluate patients for various conditions.  Today, I want to focus on pneumothorax, pleural effusions, as well as telling the  difference between A lines and B lines, which will help us to better understand if a patient might  have pulmonary edema or pneumonia. To get started, we'll- we'll start with pneumothorax. Now  as a hospitalist, I don't diagnose a lot of pneumothoraces, right? My colleagues down in the  ED are usually checking this out more than I am, but it can be useful, especially after performing  a procedure where pneumothorax is possible.

[00:00:46]Now using ultrasound to look for pneumothorax  is really nice because it's quick and it has a very very high  negative predictive value.

[00:00:54]If I perform the scan, I can say with confidence  that my patient doesn't have a pneumothorax.

[00:01:00]This -the sensitivity of this scan- is is such  that when you perform it, you well outperform a chest X-Ray, and you approach a CT scan in terms  of the negative predictive value, which is why so many of us like doing the scan this way. Now, to  get started, we're going to position our patient, and then we're going to grab a probe. I'm going  to show you all today using a linear probe. Though to be honest with you, you could do this scan  with many different probes, and it works. But we'll be able to see the best today with a linear  probe, so I like to- I like to show you with this.

[00:01:32]When we position our patient, we'll  usually have the patient lying flat.

[00:01:36]Okay, we can have the bed up maybe a little  bit. Like here, we have a pillow under his head, but it's really important because air is going  to rise and we want to put the probe where the air would go, right? If we have the patient  sitting straight up, the air is going to come up here to the clavicles, and we actually can't  see very well the sliding that we need to see up here above the clavicles. So what we need  to do is scan with the patient lying flat.

[00:02:01]I'm going to place the probe across a couple of  rib spaces here, and this is about the highest part of the chest here. So this is where the  air should go, and if we go, we can see here, I've got a beautiful picture of two ribs and the  space right in between. Alright, I'm going to look for that bright white line. That bright white line  is the interface between the visceral and parietal pleura. If I see movement along that bright white  line, I sometimes call it ants on a log. You see these little things kind of moving back and  forth, right? So long as your patient's breathing, you'll see that movement. Alright. That lets you  know that there's no pneumothorax. What happens is if there is a pneumothorax, air will come  in between the visceral and parietal pleura, and it won't let you see that movement any longer.  So if you don't see any movement between that rib space, you need to stop and think: you  might be dealing with a pneumothorax here.

[00:02:49]But as long as I see movement as I do today, I can  feel confident my patient is not in pneumothorax.

[00:02:55]So our patient today did not have a pneumothorax,  but let's go ahead and take a look at a video of what a pneumothorax would look like  if our patient had one. So here again, we can see that spot in between the two ribs  and the bright white line. Okay, again, that's your- that should be your pleural interface. Now  before, we saw that sliding. We saw it look like there were little ants moving back and forth  along that white line. But here in this video, there's nothing, right? And the reason for that  is we're really only seeing the parietal pleura, and there's air between the parietal  pleura and the visceral pleura.

[00:03:28]Alright. Or at least that's our assumption.  Now, there are a few things that can cause an absence of lung sliding, and it's important  that you know that. So we do know that the positive predictive value of lack of lung sliding  isn't nearly as good as the negative predictive value of seeing it. So if we go ahead and look  and we don't see lung sliding, you cannot assume that you found a pneumothorax. You either need to  do additional studies to try to figure this out.

[00:03:53]So what I want all of you to be good at though  is: can you identify a lack of lung sliding to know that it's time to do additional studies? And  here in this video, we can clearly see there is no lung sliding at all, and we should be nervous  that this patient may have a pneumothorax.

[00:04:10]Next, we're going to learn about how to look  for pleural effusions. This is a scan that I use all the time. Pleural effusions are  pretty easy to find with ultrasound, and it's very very sensitive. You're going to find  ultra- you're going to find pleural effusions that you don't see with the chest x-ray, but you can  pick up with ultrasound. It's sensitive for very very small amounts of fluid. So how do we do  this? We first need to position our patient.

[00:04:32]This is where you want to ask your patient  to go ahead and take your right arm.

[00:04:36]We're going to start on the right side and place  it behind your head. We want to be able to expose the entire side of the chest here, including the  axilla. Then you can use either a cardiac probe or an abdominal probe: the curvilinear probe.  But I prefer the cardiac for this scan, and I'm going to place the probe with the probe  indicator. And that's a little different on each- on each device. This probe indicator is this  little bump here. Okay, I want to place that superiorly headed towards the axilla, and I'm  going to place the the probe itself somewhere between the mid-axillary and the posterior  axillary line. So again, if we look here, this is our mid-axillary line here. This is the posterior  axillary line. So right in this space here, and I'm going to be looking through the liver. My  goal is to see the liver. Once I find the liver, I'm going to aim my beam up into the chest, right?  So here we can see we've got a nice image of the liver. That bright white line, that big curved  line there, that's the diaphragm, okay? My goal is to see to the other side of the diaphragm, so  what I do is I rock the probe, okay? And because I want to head up farther into the chest now. If we  watch the screen, we can see the diaphragm moving.

[00:05:46]Okay, our patient's diaphragm works. That's great.  We can also see this sort of scalloped look sort of along the bottom of the screen. Okay, the  diaphragm kind of merges with that scalloped structure there. What we're actually looking  at is our patient's spine at this point. Okay, we're seeing all the way to the mid-chest. That's  the spine. Now, what we're going to look for is we're going to see: does the spine go past the  diaphragm? If the spine goes past the diaphragm, you're looking at an effusion, right? Because  remember, on the other side of the diaphragm, you have lungs that are full of air. You can't see  through them, right? You wouldn't be able to see past the lungs to see the spine. But in this case,  we can see just as we expect. As soon as we hit the diaphragm, we cannot see the spine anymore.  We know that our patient here does not have any effusion on that right side, so we can feel  very confident in ruling out a right-sided pleural effusion. Next, we're going to do the left side of  the chest. Now, the left side's a little bit more difficult than the right for a couple different  reasons. First is our window. Now, instead of the liver is going to be the spleen. And as you  all know, the spleen is considerably smaller and a bit more variable in terms of the the size, and  the way it's sort of rotated inside the abdomen.

[00:06:55]And so it's a little harder to find and a little  harder to use as a window compared to the liver.

[00:07:00]Similarly, you also have a stomach bubble  here, which can be full of air if the patient's eaten recently. And so that can also be  a little bit of a challenge when you're trying to get that crisp clean image that  you want, but don't get frustrated. We're going to- we're going to figure this out. So  first, let's position our patient and let's go ahead and have your left hand go behind your  head. You can bring your right hand back down, and we're going to put some gel here on our probe.  Just like on the right side, we're going to get our probe indicator. Some people call it the dot.  On this kind of this machine- this is our dot, okay? And when you want to find the spleen. Okay,  usually you're going to go you know somewhere again between mid-axillary and posterior axillary  line. Sometimes, it's helpful to actually find the kidney and use that to find the spleen, and there  I'll go all the way to the posterior axillary. But let's go ahead and place the probe right about  here. I'm going to slide around until I find the spleen. Now again here, we're pretty lucky.  We've got a beautiful picture of the spleen.

[00:07:55]Again, our probe indicator is pointed towards the  axilla, alright? And we're pretty happy with our picture, and now we're going to see can we make it  any better? Oh, now it's a little bit better. Now, I can see the spine there. I can see the  diaphragm, and so I'm pretty happy with this. I feel pretty confident. Again, since I  don't see the spine continue past the diaphragm, that has ruled out even a small pleural effusion.  I feel pretty good about this image, but sometimes you're not going to be this lucky. The left side  can be more difficult, so there will be times where we need to take a different approach. So  for this, what I'm going to have our patient do is just go ahead and take a big deep breath. Let's  see what happens here. Keep going keep going keep going. And notice with that big deep breath,  suddenly the whole screen went gray. Alright.

[00:08:38]When that happens, what's occurring inside  the body is that his diaphragm now just moved, and now we've got air in between our probe and the  spleen, okay? That made our screen go fuzzy. We've essentially ruled out a large pleural effusion  by doing that. We call that the Curtain Sign.

[00:08:56]Now again, could you have a small pleural  effusion? Yeah, but again, sometimes when you're evaluating a patient, you can't get that perfect  picture. You can use the Curtain Sign to at least look and make sure that it's not you know a large  pleural effusion causing shortness of breath.

[00:09:10]Next, we're gonna go ahead and take a look at a  video of what a pleural effusion actually looks like. Today, our patient was healthy. He didn't  have any pleural effusions, but these are things that you will definitely find in your hospital  practice, so it's important that you get to know what you're looking for. So as we talked about  before we were scanning, we're looking right at the the base of the diaphragm there to see: does  the spine continue past the diaphragm and into the thoracic cage? Normally, again, we can't see that  because there's air in the way. But if there's fluid there, that fluid is going to give you a  great view of the spine. Now as soon as you see it go past like that, now you need to explore  this effusion a little bit. Alright. And so in this video, we can clearly see the spine moving  past the diaphragm, and then especially if we angle the probe a little bit more anterior, we're  actually able to see a bit of atelectatic lung, so a little bit of collapsed lung that's floating in  that fluid move in and out of our screen. We have clearly diagnosed a pleural effusion. You can also  look around to see: well are there any septations?

[00:10:08]Okay, is there layering layers within the fluid?  Is the lung tethered and not able to move? Or is it moving around freely as the patient breathes?  All this is going to give you some idea of whether or not this is a free-flowing effusion or  whether it's loculated or even an empyema.

[00:10:25]Up until now, we've really just looked at the  the area around the lungs. Now we're going to move into actually examining the lungs themselves,  and this is where it's really important that we learn about two different artifacts: A-lines and  B-lines. So to do this, well I'm going to show you a video clip here of A-lines and B-lines. We'll  start with A-lines. A-lines are considered normal, okay? If you are healthy and well, when I examine  your lungs, I should see A-lines. What are they?

[00:10:50]Well, when I place the probe under the chest and  I look between the ribs and into the lung tissue, what I'll see are repeated horizontal lines here,  okay? They start from the pleural interface, and they're actually at repeated repeating depths  below that. And that is an A-line. We think of that as: well, there's normal tissue right below  my probe. I'm not seeing deep into the lungs, so you really want to be careful. I'm really only  able to say right at that interface, that there's normal lung tissue there. Could there be something  hidden deep that you can't see? Yes. So again be careful you have not ruled out any bad pathology  there, but you have ruled out pathology right underneath your probe if you see A-lines. Now  occasionally, if your probe is not perpendicular to the pleural interface, you won't be able to  see A-lines. And so it does require a little bit of moving the probe back and forth to make them  pop out. Next are B-lines. This is the most common pathology that you're going to find when you go  ahead and examine the lungs. B-lines as opposed to horizontal, these are vertical lines. They also  start at the pleural interface. Now for it to be a true B-line, in the lung ultrasound setting,  so set it about 13 centimeters, the streak artifact will start at the pleural interface  and go all the way to the bottom of the screen.

[00:12:04]Similarly, it also needs to move as the patient's  breathing, so as we look at this video we can see that it's moving back and forth. It comes  and goes, okay? So if they're not- if they're fixed in place, that's not a B-line. It needs to  look like these guys. They move back and forth.

[00:12:19]Similarly, they can be of different widths.  Some can be narrow. Some can be large.

[00:12:23]Again, when we're looking at this video here,  we want to get a sense of: well is that a lot of B-lines? Is that not too many B-lines?  There's two different ways to quantify that.

[00:12:32]One you can just count the number of B-lines that  you see, okay? The more, the worse it is. Or you can actually see how much of the screen they  take up. So B-lines can get quite fat and then can suddenly take up a lot of the screen. When you  see that, that also means the pathology is worse.

[00:12:49]Now we're ready to go ahead and take a look at  the lungs themselves. When we do lung ultrasound, there is not one defined way to do this,  and that's really important to remember. It depends a little bit on how sick your patient is,  right? So if my patient right now is an extremist, he's ready to get intubated. Because he's so  short of breath, I may not need to do that many windows to understand what's wrong with the  patient. However, if my patient's completely healthy and I'm looking for very subtle signs of  pneumonia, I need to do a much more thorough scan to really feel like I've ruled that out. And  at this point where we are on lung ultrasound is: there's many different protocols that are out  there in terms of the number of windows you get.

[00:13:27]And again, for all of you, it might  really depend on your clinical setting, how sick your patient is, and that's going to  help you to understand well how many parts of the lung do I need to look at to feel certain  that I've learned enough to make a diagnosis?

[00:13:40]The other thing I want you to think about is  we're all used to thinking about the lungs in terms of chest X-Rays, and I still think that's  helpful to me. So when I go ahead and scan, I'm almost building a chest X-Ray in my head.  Where do I see pathology? Is it on the left side? Is it on the right side? Is it diffuse? Do  I see it everywhere or is it just in a few spots?

[00:13:59]The way I want you all to think about it is:  when we find pathology, when we find B-lines, you can think about that as an opacity on  chest x-ray. It's clearly a problem area that you're going to need to explore more.  How do we go ahead and get these images?

[00:14:14]I'm going to go ahead and use a  cardiac probe here. Though again, you could use other probes. For lung ultrasound,  it's pretty straightforward. Many of your machines now have a lung ultrasound setting and that helps.  It'll set our depth to the appropriate depth.

[00:14:32]Again, just by convention, I'm going to have my  probe indicator pointed up, okay? And for this, I'm going to go ahead and show you four  points on the chest where we're going to look.

[00:14:44]On the left hand side, it's actually a little bit  harder because we need to avoid the heart. Again, we're going after the lung here, so we'll  place the probe where we think we're at least on this side above the heart. And here  we can see beautiful A-lines. I can feel really confident that's normal, right? This is not a  technique heavy scan. I'm just placing the probe, and I'm looking to see what I see, okay? It  doesn't require a lot of of changing the angles or anything like that. Now occasionally, if I don't  see the A-lines pop out, I might need to adjust a little bit to make sure I'm perpendicular.  And now I've got some A-lines, I can move on.

[00:15:17]Okay, I'm going to come. Again, I'm trying to  avoid the heart and so I'll come over here and again, I'm going to adjust my angle a little bit  and boom: there are my A-lines. Perfect. Now, we're going to come over here and see. Again,  can I get around the heart? No, I can't, so I still got heart here. I'm going to move over  here and now now I'm a little bit below the heart, and we'll see if we can get some A-lines to  pop out for us. Okay and there we go. Now depending on what you're scanning for, you  might then go and look for a pleural effusion.

[00:15:48]You may have the patient sit up, and you may need  to now scan all those areas of their back as well, okay? Because again, I've only looked at the left  anterior side of the chest. I could also come over here to the right side and take a look over  here again. Again, I see nice A-lines pop out.

[00:16:03]Right side's a little easier. I don't have  to contend with the heart, so it should be a little bit more straightforward. Again, I'm  going to angle the probe a little bit. And now, I get my A-lines. I can feel good that we  got a nice view there. I can come down here.

[00:16:14]Again, easier because there's no heart in the  way. I got A-lines, and I would just continue to do this. This would be an eight-point scan where  we do four areas of the chest here. We can combine that by looking at the mid-axillary lines.  We can look for pleural effusions and again, if you need to be really thorough, we can sit the  patient up and scan their entire back as well.

[00:16:34]How are we going to interpret this? Okay, and  this is where it gets a little bit tricky. The technique is easy. We found A-lines and B-lines no  problem. Just placing the probe in between the rib spaces. It's going to be the interpretation  that's a little bit more tough, right?

[00:16:47]Here, we need to really use our  skills of clinical integration, so let's let's imagine we're doing our scan and  we see a lot of B-lines and it's just over this area of the chest, right? It's just on  the left side of the chest. Well that would be concerning that perhaps the patient has a  focal pneumonia there, right? It's certainly something that's not widespread. It's in just one  small area. Similar it is if you had a chest x-ray and you saw an opacity on the left side, you might  say: oh perhaps this patient has a pneumonia. We still need to use our clinical integration. Does  the patient have a fever? Does this patient have a white count? How do their lungs sound? Are they  producing sputum? Again, clinical integration here is key. Now similarly, if I looked and everywhere  I place the probe right, I see B-lines everywhere, and maybe there's some small pleural effusions  on both sides. Okay, well now I'm thinking: well this is most likely to be pulmonary  edema. It's a diffuse process over both lungs. And again in the right clinical setting,  I should be very very concerned that perhaps the patient has pulmonary edema. It's going to be all  about the patterns of pathology that you find.

[00:17:48]Now the last thing I'll say, especially someone  who works in the hospital, is the the key to clinical integration here is that you're going  to have patients who are maybe a little bit sick, maybe a little bit short of breath, and you find  a little bit of pathology. The hard part for all of you is gaining enough experience to say: did  I see enough pathology there to explain the level of illness that I'm seeing? Okay, my patient's  on 4 liters nasal cannula satting 96 percent, and I saw a few B-lines. Is that enough to  explain that level of hypoxemia? Perhaps not, okay? And this is where again when you're done  today with watching this video, you're not ready to answer that question. You're going to need  to get some practice and to do some scanning to start working on your clinical integration,  so you can feel much more confident that those few B-lines didn't answer your clinical question.  You need to look for what else could be going on, [Music] [Music]