Point-of-care ultrasound (POCUS) has revolutionized the way critical care medicine is practiced, with its main use being quick assessments of the heart, lungs, and inferior vena cava. Beyond these common applications, POCUS is proving to be a useful tool in quantifying venous congestion, confirming endotracheal tube placement, and assessing mechanical ventilation readiness and liberation.
During the CHEST 2021 session The Wave of the Future: Beyond the Ultrasound Basics, a panel of experienced intensivists discussed these and other POCUS applications in the critical care setting.
Orlando Garner, MD, a critical care physician at Midland Memorial Hospital in Texas, began the session with a review of the utility of neuro-ultrasound, including transcranial doppler (TCD) and optic nerve sheath diameter measurement as tools to evaluate intracranial pressure and other parameters.
“Transcranial doppler ultrasound has many of the benefits that regular point-of-care ultrasound has, being that it’s reproducible, easy to perform, and it’s noninvasive,” Dr. Garner said. “But it also has some of the same disadvantages that ultrasound has, such as user variability and operator dependence.”
While TCD does not replace CT or MRI imaging, he said it can be a convenient adjunct to help clinicians interrogate for intracranial pressure, vasospasms, midline shift, and circulatory arrest.
In the next presentation, Ali Omranian, MD, Assistant Professor of Critical Care Medicine at the Baylor College of Medicine, discussed the use of ultrasonography in examining the upper airway and its utility in critical care procedures, such as confirming esophageal tube placement in intubated patients.
“With ultrasound, an intensivist would be able to confirm their tube placement, with or without the help of another person at the bedside,” Dr. Omranian said. “Once the tube is in, I start scanning the lungs and trachea, which requires a scanning before to know the anatomy and see what things look like at baseline, and then compare that after intubation.”
The utility of this method of confirmation, he said, became especially clear during the height of the COVID-19 pandemic and led to the development of a tube confirmation protocol at his institution.
“At the time we started the protocol, it was very helpful because obtaining x-rays after intubation was taking a lot of time—so many x-rays were happening around the hospital and techs were busy,” Dr. Omranian said.
Philippe Rola, MD, Chief of Service in the Intensive Care Unit at Santa Cabrini Hospital in Montreal, followed with a presentation on the use of ultrasound to evaluate venous congestion.
“This has largely been a topic that has not received the attention it deserves, because much of the focus has been on the forward flow,” Dr. Rola said. “And that makes sense, as it’s our simplest surrogate to perfusion and adequacy of cardiac output. So, we don’t routinely focus on the venous side of circulation, but I think it’s something that we’ll see deserves more attention in the coming years.”
Traditionally, he said that approaches have focused on measurement of the inferior vena cava (IVC) in long axis at a point below the diaphragm, but emerging approaches involve 3-dimensional or short-axis viewing, which has been shown to improve detection of a plethoric IVC with fewer false positives.
“Using these types of views, we get a better correlation between the inferior vena cava and the central venous pressure,” Dr. Rola said. “I think around the corner is the rise of microcirculatory monitoring, including the microcirculatory indicators and patterns of flow that go with venous congestion.”
In the final presentation, Alfredo Iardino, MD, Pulmonary and Critical Care Medicine Chief Fellow at the UNLV Kirk Kerkorian School of Medicine, reviewed the use of POCUS in ventilator liberation.
“Point-of-care ultrasound weaning protocols are usually done before, during, and after the spontaneous breathing trial and should be directed to the heart, lungs, and diaphragm, to look for pulmonary edema, derecruitment, and weakness, respectively,” Dr. Iardino said.
POCUS is not often used to assess the diaphragm, but he said it can provide important information in making the decision to liberate a patient from mechanical ventilation.
“It’s important to remember that the diaphragm actually makes 80% of inspiratory effort, so a combination of 18 to 69 hours of diaphragmatic inactivity results in marked atrophy of the muscle due to proteolysis during inactivity,” Dr. Iardino said. “What happens when the muscle starts working again, when you extubate the patient, there is high activity of proteolytic enzymes in the muscle, and the muscle will actually get more atrophied.”
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