This transcript has been edited for clarity.
Elaine I. Yang, MD: Hi. My name is Dr Elaine Yang. I'm one of the critical care anesthesiologists at Hospital for Special Surgery (HSS). I'm here with my colleague, Dr Stephen Haskins.
Stephen C. Haskins, MD: Hi, and I'm also an anesthesiologist here at HSS. Today we are going to be discussing some of the benefits of point-of-care ultrasound in the perioperative setting, and we will be doing a brief demonstration on how to perform it.
Yang: Stephen, can you show us or tell us how point-of-care ultrasound differs from a formal ultrasound?
Haskins: When we think about formal ultrasound, generally speaking, we are referring to an ultrasound that may be performed either at the bedside or in a specific location, usually by a technician or by a radiologist, or a cardiologist and an echocardiography technician. These are complete and formal exams that are used for very specific diagnostic purposes.
Point-of-care ultrasound is conducted at the bedside as well, but it's performed by the clinician who is managing care for that patient. It helps answer specific questions that are related to the patient being in some sort of acute- or critical-type state. That includes patients who may be hemodynamically unstable, showing signs of undifferentiated shock. They may be in respiratory distress. We're trying to differentiate between some of the major causes that are resulting in this presentation and ultimately trying to help us guide management of the patient at that specific moment at the bedside.
Yang: What type of training is needed to conduct a competent exam at the bedside, and how do you continue to certify clinicians on an ongoing basis?
Haskins: Different skills require different levels of training and numbers of exams to be performed to get to the point where you are competent. I would say, arguably, that the most challenging one to really be considered competent in would be echocardiography. It requires much more skill and nuance to be able to visualize and scan the heart. In anesthesiology, we are most familiar with echocardiography, mainly in the sense that we use it often for transesophageal echo in the cardiac operating rooms.
There's been a movement toward using transesophageal echo for that cardiac patient undergoing noncardiac surgery. Lung ultrasound, airway ultrasound, gastric ultrasound, assessment of free fluid in the peritoneum (these are all things that I'm going to demonstrate briefly)—they don't require nearly as much time in terms of training and supervised exams before one can become competent in it.
Certification is not available yet for the general anesthesiologists. There is a certification pathway that will be available, most likely through the National Board of Echocardiography, for critical care physicians. Right now there is a process underway to, hopefully, develop a certificate of completion through the American Society of Anesthesiologists, so that the general practitioner will have a way of demonstrating their competency and, therefore, have the ability to use that as a means to get credentialed at their local institution.
Airway Ultrasound
I'm now demonstrating airway ultrasound. This is a cephalad orientation; this is caudad. These are the tracheal rings, which have been described as a string of pearls or sausage links. This is a way for us to identify midline. We see this very bright, hypoechoic air-tissue interface. We can visualize that because these are cartilaginous structures, which means that the ultrasound beams are able to penetrate through them, whereas with bone, we would see dark, acoustic shadowing underneath it.
What is going to be most meaningful for us is to be able to visualize, is the cricoid cartilage. Lying in between the cricoid cartilage and the thyroid cartilage is the cricothyroid membrane. That's our emergency airway— if you lose your airway, you can't intubate or ventilate. To be able to visualize that and confidently mark that out prior to induction on a patient with a large neck (where you wouldn't be able to normally feel the cricothyroid membrane), you can use that to perform the procedure.
You can also visualize the esophagus. My probe is still placed in a transverse orientation, but now I've tilted the tail of the probe toward the left shoulder. Usually, just above the sternal notch is where you can very confidently see the esophagus off to the left side.
As he swallows, we observe a little bit of air and some fluid moving down the esophagus. If you are concerned that your endotracheal tube is in the esophagus, then what you would see is this double trachea sign. Instead of this nice, muscular structure off to the side, you'd observe what appears like a second trachea next to it.
Lung Ultrasound
The next skill that we'll demonstrate is lung ultrasound. When it comes to evaluating the lung, there are a few things that you can look for. A pneumothorax is a very common indication for performing a lung ultrasound exam. It actually has been shown to be more sensitive and more specific than a chest x-ray. It is the better imaging modality at the bedside to evaluate patients for a pneumothorax.
You'd want to position your patient to allow air to rise into the anterior portion of the chest. Ideally, when they are supine, that's going to be between the second and fourth intercostal space, right where you would do a needle decompression on a patient who has a tension pneumothorax.
First, I want to identify two ribs. The ribs have this dark, acoustic shadowing underneath them. Notice that my probe is oriented in a sagittal plane and pointed in a cephalad manner, which allows me to visualize these two ribs as they are running perpendicular to the probe. It also allows me to confidently identify this bright, shimmery, shiny line just deep to those ribs—the pleural line. That's where all the action is when it comes to evaluating the lung.
This shimmery, shiny, back-and-forth movement is lung sliding. That can allow you to rule out a pneumothorax in the location that you are currently scanning.
Here are two pleural layers: the visceral pleural, which is adherent to the lung, and the thoracic parietal pleura; and the two are sliding up against each other. I want you to take a big, deep breath in for me and hold it.
Now instead, we're going to see something that appears more like a pulsatile-type nature. That's called lung pulse. It also allows you to rule out a pneumothorax, and it's something that's often seen in patients who are apneic.
The heart, as it beats, physically moves the lung and pumps blood into the pulmonary vasculature. That allows those two pleural layers to interact with each other that way. Again, that's another way to confidently rule out a pneumothorax.
The last thing that we can do is place M-mode on our image, which will give us this image of a seashore sign.
The chest wall has very minimal movement and looks like ocean waves. Down here in the lung tissue, when there is movement as a result of lung sliding or lung pulse, we're going to observe this sandy, homogeneous, granular appearance. If we see that seashore sign, it also allows us to rule out a pneumothorax.
Another indication for the use of lung ultrasound is if a patient is showing signs of respiratory distress that isn't related to a pneumothorax. So, that could be the result of an interstitial syndrome. The way you might see a diffuse interstitial syndrome, such as congestive heart failure, acute lung injury, or acute respiratory distress syndrome, is via a predominance of B lines. Fortunately, our model is quite healthy and his lungs are quite aerated, so we're not seeing any B lines. B lines appear as a rocket, a comet, or a laser-type artifact that usually emerged directly from the lung tissue, immediately underneath the visceral pleura, and would go all the way down to the edge of the screen.
By seeing that, it means that there's no air in between those two pleural layers, and therefore it rules out a pneumothorax. A significant amount of B lines, either diffuse, throughout the lungs, or focally, as you might see with a pneumonia—say, in aspiration pneumonia where you'd only see B lines focally in the right upper lobe and the rest of the lobes would be clear—can help you differentiate among causes of respiratory distress in the perioperative setting.
Cardiac Ultrasound
The next imaging modality I am going to demonstrate is focused cardiac ultrasound. I do want to be clear and differentiate that from a full echocardiogram. This is not meant to be performed to diagnose nuanced pathology but instead to look for that gross and obvious pathology that often is the cause of undifferentiated shock.
This is a very powerful and meaningful tool for the patient who is hemodynamically unstable, and it's to help us see things like, is my heart working well or is it working poorly? Is there fluid around my heart? Does my heart look empty or does it look full? We look for signs of volume status. These can all guide management.
Ultimately, patient positioning can significantly improve your imaging. We recommend, if you can, having your patient lie on their left side, so that the heart falls forward and comes closer to the chest wall. But often, in the operating room, that isn't a possibility. I want to demonstrate how, even in a supine position, you can actually get fairly good imaging. This is our parasternal long-axis view, where we see the right ventricle here in the near field. This is our left ventricle, aortic valve, ascending aorta, mitral valve, and left atrium. We're getting a lot of meaningful information here about cardiac function, volume status, and signs of any significant valvular disease in a very short period of time. We can also evaluate for any black ribbon surrounding the heart that would be indicative of a pericardial effusion.
We have a slightly more involved tutorial that is available through the HSS academy on the Focus Assessed Transthoracic Echocardiography (FATE) exam. One of my colleagues, Jemiel Nejim, goes through all of the views in a little more detail, so if you'd like to access that, you can just follow the link.
This is our parasternal, long-axis view for this image. I basically just have my probe between the second and fourth intercostal space, and the orientation marker is pointed directly at the right shoulder. In order to see a short-axis view, I'm going to now take my probe and I'm going to rotate it 90˚ clockwise, so that way it's pointed toward my patient's left shoulder. This gives us an image of our parasternal short-axis view, midpapillary, where we can see the papillary muscles. This is another very meaningful view that allows us to get insight into cardiac function. It is where you would look for signs of myocardial ischemia and where you'd see regional wall motion abnormalities.
The next view I'm going to demonstrate is the apical four-chamber view. What you want to see here is the apex of our left ventricle, centered in the screen. This is our left ventricle, the mitral valve, and left atrium. This is our right atrium, tricuspid valve, and right ventricle. This is a traditional apical four-chamber view, another meaningful way to evaluate cardiac function. It gives you insight into the size of the right ventricle over the left ventricle. That would be particularly important in a patient in whom you're concerned about a pulmonary embolism, where you would have acute increase in right ventricular pressure, and therefore the right side would be much larger than that of the left ventricle.
Next we're going to look at the subcostal view. We have a four-chamber view in this setting. My probe is directly underneath the xiphisternum, and my orientation marker is pointed toward the left, usually with a little bit of counterclockwise rotation. The four-chamber view gives us very gross but meaningful insight into cardiac function, the relative size of the right ventricle to the left ventricle, and we can also see the tricuspid valve and the mitral valve.
Now I'm going to take my probe and rotate it 90˚ counterclockwise. I'm going to assess for the inferior vena cava (IVC). The IVC is a large vessel that tracks through the liver and goes directly into the right atrium.
This allows us to get general insight into a patient's volume status, because the diameter and the collapsibility of the IVC often correlate with the patient's volume status if they have relatively normal right heart function and valves. In a normal patient, you'd expect your IVC to be around 2 cm in diameter, and you'd also expect to see somewhere around 50% collapsibility with normal tidal volume breathing.
Another way to get more specific insight into the size and collapsibility of that IVC is to place M-mode within a few centimeters of the IVC-right atrial junction. We can see with respiration the collapsibility of our IVC. That's something that we can visualize and potentially even measure with our tools at the bedside.
Gastric Ultrasound
The last clinical skill that I am going to demonstrate here is gastric ultrasound, specifically the use of ultrasound to identify the gastric antrum. This is beneficial when you are about to induce a patient and are concerned that they may not be adequately nil per os (NPO)—nothing by mouth. And that could be a patient who has fasted for 12 hours but has some form of pathology, like diabetic gastroparesis, or some sort of critical illness or neuromuscular disorder that can result in delayed gastric emptying, or in a patient where it's impossible to confirm their NPO status. Perhaps you have a trauma patient who is unconscious or someone who is delirious or demented, or there are language barriers. This is a tool to help us evaluate the gastric antrum reliably and determine whether a patient is considered high risk for aspiration or incredibly low risk.
We are going to take this abdominal probe in our adult-sized patient—in pediatric, you would use a linear probe—and place it in the epigastric area, in the sagittal plane. The first thing that I do is I identify the abdominal aorta in long axis. We can see this large, tubular structure that is pulsatile. Now that I have identified the aorta, I can look for the gastric antrum. The gastric antrum is going to be sitting right here, sandwiched in between the left lobe of the liver and the pancreas down here. We can also see the branch of the superior mesenteric artery coming off of the aorta.
That's how we're able to confirm if a patient is NPO or their gastric antrum is empty. We can see that by visualizing the bulls-eye sign or target sign, where you observe this hypoechoic, thick, muscularis layer. Then you're going to see the gastric mucosa and a nice, empty antrum on the inside.
Right now, this gastric antrum looks fairly empty. It looks like a pancake in shape and is relatively flat in between peristaltic contractions. As the stomach contracts, you again see this bulls-eye–type of appearance. It's important to note that a patient's stomach is not considered empty or NPO unless they are on their right side. Having your patient turn onto their right side allows for gravity to cause any liquid or food solids that may be sitting in the gastric fundus or body to then pool within the gastric antrum.
Qualitatively, supine, our patient's stomach looked empty. As we turned him onto the side, what we see is this—a late-stage solid. That's the breakfast from earlier still swirling around within the gastric antrum; therefore, this patient would still be considered a relatively high risk for aspiration as a result of still having a significant amount of particles within the gastric antrum.
Again, it's important to make sure that, if possible, you scan the patient in both the supine and the right lateral decubitus position. If they are empty in both positions, then they are considered incredibly low risk for aspiration.
Butterfly iQ Handheld Ultrasound
This is the Butterfly iQ, one of the many hand-held devices that are available on the market right now. I'm going to choose one of the many presets—cardiac. The probe will automatically adjust to a phased-array type of imaging modality. The device can do abdominal scanning, which usually is a more curvilinear type of imaging. It can also be used for lung ultrasound or to scan nerves. I would say that the largest benefit to having all of these presets is that it allows you to do all of the scanning with one probe. When we use our traditional probes, which have piezoelectric crystals, we end up needing to switch from one probe to another, depending on the exam that we are doing.
I'm going to do a head-to-head here. This is what the IVC would appear like, using our cardiac setting with the Butterfly iQ. The imaging is similar in the sense that it gives you the gross information that you need, which is that the IVC is normal in terms of its size and collapsibility. You can adjust the imaging. As we were able to perform M-mode with the other, more advanced ultrasound machine, we can also do that with our Butterfly iQ.
The biggest benefit to having a device like this is its portability—to be able to pull it out of your pocket and immediately start using it, instead of getting a large machine and dragging it into a room, and dealing with the inconvenience of that. The imaging is excellent enough to get the information that you need to guide clinical management.
Thank you so much, again, for joining us here at HSS in our collaboration with Medscape, discussing the role of point-of-care ultrasound for a clinician in the perioperative setting.
Feel free to access some of the resources that were made available throughout the video, including the links to focused cardiac ultrasound and lung ultrasound scanning tutorials, as well as some of the additional educational review articles on point-of-care ultrasound.
Resources
The Focus Assessed Transthoracic Echocardiography (FATE) Protocol
Lung Ultrasound for the Regional Anesthesiologist and Acute Pain Specialist
Focused Cardiac Ultrasound for the Regional Anesthesiologist and Pain Specialist
Gastric Ultrasound for the Regional Anesthesiologist and Pain Specialist
Stephen C. Haskins, MD, is a clinical assistant professor of anesthesiology at Hospital for Special Surgery/Weill-Cornell Medical Center in New York City. As an attending anesthesiologist, Haskins leads the Department of Anesthesiology, Critical Care & Pain Management's point-of-care ultrasound education.
Elaine I. Yang, MD, is a board-certified anesthesiologist and critical care physician at Hospital for Special Surgery. Her expertise lies in the treatment of critically ill patients after complex surgeries and the use of ultrasonography in the routine management of these patients.
Follow Medscape on Facebook, Twitter, Instagram, and YouTube
© 2019 WebMD, LLC
Cite this: Perioperative Point-of-Care Ultrasound--Do You Know Best Practices? - Medscape - Dec 17, 2019.
Comments