Hi, my name is Dr. David Martin and I'm joined by Dr. Andrea Dreyfuss. We're cofounders of Ondas de Latinoamérica, a non-profit aimed at providing ultrasound education in Latin America. Today, we will provide some background information on pulmonary ultrasound. However, we will not discuss the literature in depth and will focus primarily on acquisition and interpretation of pulmonary ultrasound images in patients with COVID-19. Additionally, we'll touch upon equipment protection and decontamination to prevent transmission of COVID-19. So Dr. Martin, what are some of the advantages of using pulmonary ultrasound compared to other imaging modalities such as chest x-ray and CT scans? Ultrasound can generally be performed at the bedside with some devices having the added benefit of being handheld, allowing the machine to be brought to patients who may be too sick to safely transport to the radiology suite to obtain a chest x-ray and a CT. The images can be interpreted by the operator at the bedside. Additionally, the exam can be repeated to monitor disease progression and responses to therapies. So how does ultrasound compare to chest x-ray and CT imaging? Before COVID, we already knew that pulmonary ultrasound was more sensitive than x-ray for identifying pneumonia. Recent studies of COVID-19 patients have additionally shown a high degree of correlation between pulmonary ultrasound and CT findings, as demonstrated by the images on this slide. So now that you are convinced of the benefits of pulmonary ultrasound, how do we perform a pulmonary ultrasound exam on a suspected patient with COVID-19? In our experience, the curvilinear probe will provide you with the best images when scanning the lungs of suspected patients with COVID-19. What if we don't have a curvilinear probe? If you do not have a curvilinear probe, you may also use to phased array probe, colloquially known as the cardiac probe. The main limitation with using the linear probe is that you will be limited to superficial structures, thereby limiting your ability to see some of the artefacts that help us identify pathology, which we will discuss in more detail in the following slides. We begin by identifying six distinct lung zones. Zones 1 and 2 represent the anterior zones and zones 3 and 4 represent the lateral zones, which are divided by the anatomical landmark of the anterior axillary line. Zones 5 and 6 are the posterior lung zones. We recommend scanning patients from behind to minimize potential risk of exposure in a sitting up position, however, if your patients are unable to sit up, one can attempt to scan the inferior aspect of the posterior lung zones by raising the patient's arm over their head and sliding the ultrasound probe posteriorly past the posterior axillary line. We begin our scan by orienting the probe perpendicular to the intercostal space as shown in the image above, making sure that our probe marker is oriented toward the person's head. The probe marker is typically identified by a marking on the actual probe, and by convention will be found at the top left of the ultrasound image above. With this orientation in place, the images on the left of the ultrasound screen represent a cephalad direction and the images on the right a caudal direction. Keeping this orientation will ensure that movements on the patients mirror movements on the ultrasound screen. You should also ensure to select the pulmonary setting on your ultrasound device if available. However, if this function does not exist on your device, we opt for the abdominal setting. Select a minimum depth of ten centimeters, however, this number may be increased in cases where there is more subcutaneous tissue or decreased when scanning pediatric patients. The goal is to scan a sufficient a depth that allows us to visualize reliably the lung artefacts we will discuss next. The basic principles of pulmonary ultrasound is that air reflects ultrasound waves and therefore normal aerated lung should appear black. Thus we can begin to see artefacts develop when lung is no longer aerated, resulting from conditions such as interstitial and alveolar edema and in more severe cases, consolidations from pneumonia. In a normal aerated lung, the only detectable structure is the pleura. The pleura is visualized as a hyperechoic horizontal line depicted as a white line in the diagram above. The pleural line moves synchronously with respiration and its movement during respiration is referred to as lung sliding. Lung sliding results in the creation of A-lines, a reverberation artefact which can be seen as hyperechoic horizontal lines arising at regular intervals from the pleural line. The ribs create a characteristic shadow since bone does not transmit ultrasound waves. This characteristic shadow is sometimes referred to as the “bat sign.” This image represents a normal aerated lung. Notice the horizontal A-lines visible in the image above. B-lines are vertical reverberation artefacts that arise when the ultrasound waves are allowed to be partially transmitted due to the presence of echogenetic material within the lung, such as transudative fluid within the alveolar space. On the right, we can see an example of multiple B-lines suggestive of a diffuse alveolar process. On the left, we can see an image of a normal aerated lung in a patient with COVID-19. The first ultrasound findings seen in COVID-19 are generally asymmetric focal B-lines associated with an irregular pleural line which can be independant and/or associated with a thickened pleura. Based on our experience in Peru, we have seen that ultrasound findings typically develop seven days after disease onset, though it is important to recognize that not everyone will develop pulmonary ultrasound findings and the degree of pulmonary compromise will generally correlate with overall disease severity. Typically, these pulmonary findings first become evident in the posterior and inferior lung zones. As the disease severity progresses, we can see development of multifocal B-lines, which are typically asymmetric, interspersed with areas of normal lung. The pleural line also begins to become fragmented due to the presence of small subpleural consolidations, which are defined as areas of disruption in the pleural line with multiple intense hyperlucent B-lines. The anterior zones become compromised as disease severity worsens. We begin to see coalescing B-lines, which are large areas of confluent B-lines, sometimes described as taking on the appearance of a light beam originating from the pleural line. Additionally, we see subpleural consolidations increasing in quantity and size. Next we’ll see individual examples of each of the different pulmonary ultrasound findings in patients with COVID-19. Here we can see the presence of a focal B-lines with pleural thickening. It is important to highlight again that the ultrasound findings discussed are not specific to COVID-19 and can be seen in many other pathologies including viral pneumonias, as well as any pathological process that alters the normal anatomy of the lung. This is why these ultrasound findings must be taken in the context of the patient and the context of where you are practicing medicine. For example, in some communities where we work in Peru, there is a higher prevalence of people with lung scarring from tuberculosis, which can also present with similar focal B-lines or pleural thickening. In this patient we begin to see an increasing number of B-lines in a heterogeneous pattern. On the left of the screen, the B-lines are beginning to coalesce, indicating greater pulmonary compromise, whereas on the right of the image we’re still able to identify A-lines indicating a greater degree of aeration since as you may recall, A-lines are typically seen in normal aerated lungs. In this patient, we begin to see a clear disruption in the pleural line with multiple coalescing B-lines. Subpleural consolidations can vary in size in patients with COVID-19, but generally larger consolidations should make you think about the possibility of a concomitant bacterial process. It's also important to recognize that other viral pneumonias such as influenza, can also present with subpleural consolidations. In this patient we see coalescing B-lines throughout the entire lung field with a thickened, irregular, and fragmented pleural line. Based on our experience in treating patients with COVID-19 in Peru, patients who present with this degree of pulmonary compromise in multiple lung zones are at high risk of respiratory decompensation and are likely to require supplemental oxygenation. In this image we see a small pleural effusion which can be identified as the black or anechoic stripe along the top of the diaphragm, identified by an asterix. In this picture, the inferior aspect of the lung is also visible, which represents a consolidation. Consolidations and pleural effusions are rare in patients with COVID-19. If identified, you should consider the possibility of a concomitant bacterial infection or other potential comorbidities such as CHF. In the case of this patient with COVID-19, they were found to have an associated bacterial pneumonia. So how can you differentiate between different pulmonary pathologies and ultrasound? It's important to recognize that the pulmonary findings in COVID-19 are nonspecific and can be seen in many other conditions. This is beyond the scope of this presentation but we can combine pulmonary ultrasound with bedside cardiac and inferior vena cava views as seen above to help distinguish between cariogenic and non-cariogenic causes of B-lines. In this example, we see the above image is correlating with a patient with COVID-19, whereas the images in the inferior aspect show a decreased EF, a plethoric IVC, and multiple B-lines consistent with decompensated CHF. So what else can we look at to help us differentiate between different pulmonary pathologies and ultrasound? B-lines due to decompensated CHF tend to be homogeneous and arise from an intact pleural line as seen above on the left, compared to B-lines seen in COVID-19, which tend to be asymmetric interspersed with normal lung and arising from an abnormal pleural line. Lastly, we wanted to touch upon equipment protection and decontamination. We recommend trying to maintain some type of cover over the ultrasound probe which will be directly in contact with patients with confirmed or suspected COVID-19. We recognize this will be dependent on the resources you have available and what type of equipment you are using. The ultrasound equipment should be decontaminated using one of the EPA approved disinfectants against COVID-19 after each use and in between each patient encounter. Quaternary ammonium and isopropyl alcohol greater than 70% concentration are two of the more commonly found disinfectants, however please refer to the online website to see what disinfectants are available at your site and also the recommended minimum wait time after each disinfection, which will be dependent on the disinfectant used. In summary, we have discussed some of the pulmonary ultrasound findings seen in patients with COVID-19. It is important to remember that these findings are nonspecific and can be seen in many other pathologies, which is why it's important to take into account the entire clinical context. We would like to acknowledge our Peruvian colleagues, including Dr. Jaffryt Vargas, who provided all images show showcased in this presentation of patients with COVID-19. Thank you.
