The Dazzling Future of POCUS

Figure: Point-of-care ultrasound, undifferentiated hypotension, ET placement and depth, and necrotizing fasciitisPoint-of-care ultrasound (POCUS) in the emergency department is rapidly expanding, with newer applications for a variety of indications like improving diagnostic accuracy for patients with undifferentiated hypotension, confirming endotracheal tube placement, and diagnosing life-threatening conditions such as necrotizing fasciitis. Some studies found POCUS an accurate rule-in test for ED patients with undifferentiated hypotension, though the SHoC-ED trial, an international, randomized controlled trial, found no meaningful difference in survival between a POCUS approach to undifferentiated hypotension and a traditional diagnostic approach that did not use POCUS. (Ann Emerg Med. 2018;72[4]:478; CJEM. 2023;25[1]:48.) But a secondary analysis of the SHoC-ED study found the ultrasound arm was in line with other published diagnostic accuracy studies involving POCUS in hypotension, with overall diagnostic accuracy of around 94 percent, said one of its lead investigators, Paul Atkinson, BSc(Hons), MB BCh BAO, a professor of emergency medicine at Dalhousie University in Halifax, Nova Scotia, Canada, and the clinical academic head for emergency medicine at Horizon Health Network in Saint John, New Brunswick, Canada. “The important takeaway here is this: For many years, there was concern that we might be causing harm by taking the time to do ultrasound in these patients when we could instead be performing other tests that could give us a more accurate answer,” he said. “But this study clearly shows that there is no meaningful difference in terms of diagnostic accuracy or mortality across the population. POCUS doesn't cause harm, is at least as good as standard practice, and it offers the opportunity to be affirmatively useful in individual circumstances.”FigureDr. Atkinson noted that multiple diagnoses may not be picked up in a timely manner without ultrasound, such as pericardial effusion, cardiac tamponade, and pleural effusion, among others. “These findings give us the opportunity to speak to the potential individual benefit of ultrasound in a specific patient without being concerned that, at a population level, we may be causing any negative impact,” he said. “Let's not over-egg the pudding and say POCUS is a must-do for every patient, like ECG in chest pain.” Physicians should be aware that it causes no harm and may benefit an individual patient by picking up something that is harder to diagnose, and that it is also much quicker than many other tests, Dr. Atkinson said. “For example, in heart failure,” he said, “there is significant literature showing that you can use ultrasound for diagnosis in less than 10 minutes vs. 45 minutes to an hour with other testing.” Another interesting finding from SHoC-ED: Use of ultrasound appeared to change the preferred diagnosis more frequently than a traditional approach to diagnosing undifferentiated hypotension. “Strangely, it wasn't either more or less accurate—it just seemed to shuffle the pack a bit,” Dr. Atkinson said. “This is something we should be aware of. As physicians, we tend to be biased toward what we see on a test or screen and may give that more weight than the other information we have. I would say use POCUS with all the other tools and information you have, but don't overweight it.” He also stressed that these findings are in cases of undifferentiated hypotension. “We excluded people where we already knew what was going on or had a high level of suspicion; for example, if we felt there was a high probability of an abdominal aortic aneurysm or ectopic pregnancy because we know in those settings that ultrasound does improve care.” The SHoC studies led to the publication of an international consensus protocol for sonography in hypotension and cardiac arrest that was approved by the International Federation of Emergency Medicine. (CJEM. 2017;19[6]:459.) That protocol recommends cardiac, lung, and inferior vena cava as core views, with supplementary cardiac and other views when clinically indicated. “Subxiphoid or parasternal cardiac views, minimizing pauses in chest compressions, are recommended as core views for SHoC-cardiac arrest; supplementary views are lung and IVC, with additional views when clinically indicated. Both protocols recommend use of the ‘4 F' approach: fluid, form, function, filling,” that consensus statement noted. A 5F approach would add flow to that list. (CJEM. 2020;22[5]:655; https://tinyurl.com/27sffwe5.) Diagnosing Necrotizing Fasciitis Cases of necrotizing fasciitis (NF), which has mortality rates ranging from 20 percent to 80 percent, have increased significantly in recent years, particularly in the wake of the COVID-19 pandemic. (StatPearls [Internet]. Treasure Island [FL]: StatPearls Publishing; 2024 Jan; https://tinyurl.com/4c26897c.) “We also have more and more people on immunosuppressive agents for conditions like psoriasis, as well as increasing rates of people with diabetes, all of which come with an increased risk for NF,” said Srikar Adhikari, MD, a professor of emergency medicine and the section chief for emergency ultrasound at the University of Arizona College of Medicine in Tucson. One systematic review found that surgical debridement within 12 hours lowered the mortality rate for NF by approximately 50 percent. (World J Emerg Surg. 2020;15:4; https://tinyurl.com/4ypn4w5y.) “There is a real urgency to detect this condition, as time is of the essence,” Dr. Adhikari said. “We've heard that ‘time is brain’ with stroke; with NF, ‘time is tissue.’ Unfortunately, NF is hard to detect in some cases. These patients often present with disproportionate pain but without physical findings. We may fail to consider NF and end up discharging them, only to have them return a few hours later and end up losing the extremity.” CT has commonly been used to detect NF, but Dr. Adhikari pointed out that getting a CT may take hours because patients may be prioritized behind trauma cases. “Just sitting there and waiting for the CT delays your diagnosis and increases morbidity and mortality,” he said. “Also, in a significant number of cases, IV drug users develop this illness, and in such patients, it can be difficult to get IV access quickly. Using POCUS speeds the process up. When you have a highly suspicious POCUS, it accelerates the entire process, and the trajectory is very different than when you are just sitting around waiting to get a CT.” The ultrasound finding that is closest to 100% specific for NF is subcutaneous air, Dr. Adhikari said. (Am J Emerg Med. 2023:65:31.) “If you see air in the tissue that should not be there, that is a nearly definite diagnosis for NF unless there is an open-air wound, and you should tell the surgeon that they need an OR immediately. Other findings that are highly suggestive of NF are distorted and thickened fascial planes and fluid collection in the fascial layers of around 4 mL in thickness. There is new literature saying that as little as 2 mL points to NF, but 4 mL is highly specific. If I see that, I am very alarmed.” Practitioner skill level can be a limitation—one has to see a number of cases to recognize these findings—but Dr. Adhikari noted that it is not a complicated POCUS application to learn. “It's easy to scan and doesn't take a whole lot of effort,” he said. “The ultrasound may also need to be repeated, especially if you have nonspecific findings that could be misinterpreted as cellulitis. It is not a perfect tool, but it definitely shortens the time to consultation and to imaging and thus to operative intervention. Fascia is dying if you don't detect it. If you recognize this, you will change the trajectory and the morbidity and mortality in this group of patients.” ETT Depth Confirmation Emergency intubation requires confirmation of the accurate placement of the endotracheal tube to avoid unintentional endobronchial or esophageal placement. The 2015 Advanced Cardiac Life Support guidelines recommend capnography as the gold standard for verification of proper endotracheal tube placement, but studies have found that ultrasound is an accurate alternative as reliable as capnography with faster results. (Am J Emerg Med. 2020;38[5]:1007; Ann Emerg Med. 2018;72[6]:627.) Ultrasound guidance for intubation allows physicians to assess ETT placement rapidly at the bedside without some of the limitations faced with capnography, said Michael Gottlieb, MD, a professor of emergency medicine, the vice chair of research, and the director of the emergency ultrasound division at Rush University Medical Center in Chicago. “Not everyone has access to or uses quantitative capnography, and we know that the colorimetric version is not as accurate as the quantitative one,” he said. “Even the quantitative method does not work as well if the patient does not have adequate lung blood flow in situations like pulmonary embolism or cardiac arrest.” Dr. Gottlieb said seeing an appropriate waveform only shows that the air is getting in. “It doesn't tell you, for example, if the tube may be too high, sitting in the vocal cords where it could easily fall out or if you're too low and mechanically ventilating a single lung,” he said. “This could cause barotrauma or direct trauma from overventilating one side while the other side collapses.” Ultrasound, on the other hand, accurately predicts endotracheal vs. esophageal placement in a matter of seconds and does not require positive pressure ventilation. “You can rapidly assess the location of the endotracheal tube by visualizing it within the trachea or esophagus with the probe on the anterior neck, and then you're able to determine proper depth by simply rotating the probe,” Dr. Gottlieb said. An evidence-based review noted that POCUS is highly accurate for confirming ETT placement in adults and children, he said. (Am J Emerg Med. 2023:74:17; Am J Emerg Med. 2020;38[5]:1007.) “The typical approach involves transtracheal visualization but can also include assessment of lung sliding and diaphragmatic elevation. ETT depth can be assessed by visualizing the ETT cuff in the trachea as well as using lung sliding and the lung pulse sign,” he wrote. (Clin Exp Emerg Med. 2024;11[1]:22; https://tinyurl.com/532wpsv2.)FigureSome variation exists among physicians, and overall good data demonstrated that ultrasound at the bedside can rapidly confirm placement and depth, Dr. Gottlieb said. “As with anything, you need to make sure you are properly trained,” he said. “Just like with the bougie, a clinician should not be using it for the first time in a critically ill patient or in an extremely complex case. If you build your repertoire on simpler cases, it becomes easier to use with really complex cases that you're truly unsure about. The learning curve is relatively short, and the technique is very fast to perform. It allows you to be a better clinician.” MS. SHAW is a freelance writer with more than 20 years of experience writing about health and medicine. She is also the author of Having Children After Cancer, the only guide for cancer survivors hoping to build their families after a cancer diagnosis. You can find her work at www.writergina.com. Follow her on X @writergina. Read her past articles at http://tinyurl.com/EMN-Shaw. Share this article on X and Facebook. Access the links in EMN by reading this on our website: www.EM-News.com. Comments? Write to us at [email protected].

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