Assessing the stomach for NPO status
Learn how to use ultrasound to identify an empty stomach by recognizing if content is present.
As clinicians, we often need to determine a patient's nil per os (NPO) status. Unfortunately, patients don't always report this accurately. In this video, from our POCUS Masterclass, you'll learn how to use ultrasound to identify an empty stomach by recognizing if content is present.
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[00:00:00] We routinely need to determine nil per os or NPO status and rely on patients to report this accurately. Determining a correct time, since oral intake, helps gauge the risk of aspiration during procedures requiring sedation or anesthesia. But not all patients digest at the same rates. Some may have delayed emptying as in pregnancy, diabetes or neuromuscular disease. Ultrasound can help us determine NPO status quickly and more accurately
[00:00:30] than history alone. This lets us do a better job of assessing the risk of aspiration. In adult patients, we'll use an abdominal or curvilinear transducer, to allow for the best visualization. In pediatric patients, we can often use a linear transducer. We evaluate the stomach using two different positions. Start with the patient in supine position and place the transducer in a long-axis orientation in the subxiphoid space. Fan the transducer
[00:01:00] from the patient's right to left to obtain an image of the antrum. This creates a scanning plane, as shown here, looking through the liver and deep to the stomach. Then we repeat this process with the patient in the right lateral decubitus position. This increases the sensitivity of the exam. This transducer positioning creates an image as we see here. Our goal is to recognize the antrum, just adjacent to the tip of the liver and sitting superior to the aorta and
[00:01:30] superior mesenteric artery. The antrum has a characteristic appearance on ultrasound, with a series of layers corresponding to the layers of the stomach. There's the outermost serosa, followed by the muscularis propria, the submucosa, and then the muscularis mucosa. At the interior, we have the mucosal layer itself. Our goal here is to examine the antrum to look for gastric content. An empty stomach will have a collapsed
[00:02:00] antrum, where the anterior and posterior surfaces are in direct contact, as we see here. In this example, we see a patient with simple fluid in the stomach. The material is hyperechoic and the antrum has enlarged, as you see here. You may also notice some hyperechoic material in the fluid, this is called a starry sky appearance and can be seen in a patient who's consumed effervescent or carbonated fluid.
[00:02:30] The next pattern we want to recognize is that of a patient who has just consumed solid content. This can take on two basic patterns, depending on when the patient ate. This is the example of a patient who has just consumed solid content recently. The antrum, seen here, looks distended and the wall is thin. There is some hyperechoic material and a curtain of shadowing coming down from air, that has been entrained when the person was eating solid food.
[00:03:00] In contrast, here we see the later stage of a patient with both solid and liquid content. Now, we can see that there is some dependent hyperechoic material corresponding to the solid content and then more superficially we see hypoechoic liquid content, with some hyperechoic material in it. How can we use this information to help determine aspiration risk? Well, if you see no antral content in the supine
[00:03:30] position, the patient is low risk for aspiration. If you see simple fluid in the right lateral decubitus position, which is more sensitive but not in the supine position, they're also low risk for aspiration. However, if you see fluid in both views or any solid content then the patient is at a higher risk to aspirate. There are some populations where you should exercise special care. Be wary of
[00:04:00] using stomach ultrasound to determine aspiration risk in patients who've had prior gastric surgery for example. Ultrasound to determine stomach content may not be as accurate in this group. In pregnant patients, it may be harder to find the antrum but their baseline gastric volumes are similar to the non-pregnant patient population. Morbidly obese patients usually have an antrum that you can find but will typically have larger antral areas and baseline fasting gastric volumes.
[00:04:30] Now you know how to risk stratify patients for aspiration. You may still decide to proceed with your procedure if it's an emergency, but if you have airway concerns or the procedure is elective or not emergent, ultrasound may help you optimize your plan and timing for the procedure.