Lung ultrasound use in COVID-19 patientsby Dr. Liji Thomas, MD
Since the start of the COVID-19 pandemic in China’s Wuhan city at the end of the last year, the illness has spread across the globe to affect more than 5.4 million and has killed more than 344,000 people, mostly those who are older or have pre-existing medical conditions.
Without any specific vaccine or therapies being available, non-pharmacological interventions like lockdowns and social distancing became the norm in many countries faced with the rapid spread of the virus through brief social contacts. However, much remains to be known about the virus, its spread, as well as diagnostic and therapeutic protocols.
Lung Ultrasound: Alternative to CT of Lungs in COVID-19 Patients
One point of discussion is the best approach to imaging infected patients, because computed tomography (CT) scanning, the gold standard method for chest imaging, can spread infection due to the need to transport the patient to specialized facilities.
Many clinicians think bedside lung ultrasound could be the method of choice, with its high sensitivity for disease at the surface of the lung. This includes pleural thickening, consolidation and ground-glass opacities on CT. Recent studies report that ultrasound is better at detecting these signs of disease than chest X-ray.
Study: Lung ultrasound findings in patients with novel SARS-CoV-2. Image Credit: Sfam_photo / Shutterstock
For this reason, lung ultrasound is ideal for diagnosing many lung diseases as well as following up progression in the lungs. The advantages of this modality are the lack of ionizing radiation, no need for patient transport, and using less personal protective equipment.
The issue is the lack of data on the typical findings in COVID-19, due to the newness of the condition. The possibility of evaluating and monitoring disease progression in the lungs with lung ultrasound has to be studied. Some relevant aspects include the knowledge of how the findings change during the course of the disease and their relation to clinical features.
How Was the Use of Lung Ultrasound Examined?
Now a new Dutch study published on the preprint server medRxiv* is focused on outlining the findings in critically ill patients with COVID-19 on ultrasound of the lung, correlating them with disease duration, and finding the link between the ultrasound findings and physiological measures like the P/F ratio.
There were 75 lung ultrasound reports and 450 images for the analysis, however, about 3% were missing.
At baseline, both short and long symptom duration groups appeared similar. The BMI was 28 on average, and 90% of patients were male.
Ultrasound Findings in COVID-19
Lung sliding was reduced or absent in over a third of all views, without significant differences between the groups. A thickened pleura was seen in about 42%. A thickened and irregular pleural line was more frequently seen in patients with long symptom duration, at 21%, vs. 9% in the other group.
The images were consistent with pneumonia in about 60%. A C-profile was most commonly seen in the long symptom duration group, at 47% vs. 25%. When the PLAPS (posterolateral alveolar and pleural syndrome) point did show signs of disease, which was in about 60% of cases. In these views, consolidation was the most frequent finding, occurring in about half of positive cases.
A nonsignificant trend was observed towards a lower incidence of indicators of disease in the “short” group, but a higher number of pleural effusions in the “long” symptom group.
The researchers calculated a lung-ultrasound (LUS) score in 24 patients. The score, at an average of 20, was similar between both groups. They failed to find any correlation between the BLUE-profile and the ventilation parameters (P/F ratio), fluid balance, or dynamic compliance of the lung. The LUS score did show a trend towards correlation for fluid balance, and a weak correlation was present with compliance, but not with the P/F ratio.
Potential Limitations with LUS in COVID-19
This is the first time that ultrasound findings in a large cohort of patients with COVID-19 have been presented, in relation to baseline characteristics and using a standardized ultrasound technique. The findings show that ARDS is the most common lung presentation of COVID-19, with consolidation and interstitial pneumonia being present to variable extents between patients, but with a lower incidence of pleural effusion.
As the time since symptom onset increases, the trend of findings changes towards the increased likelihood of a thickened and irregular pleural line, pleural effusion, and C-profile. This agrees with the timeline of CT findings.
As many as a quarter of cases had non-diseased lungs on ultrasound. The investigators attribute this to the heterogeneous nature of lung involvement seen on CT, which means areas of the disease might not always be picked up. However, the LUS offers a vital clue to the presence of disease even in these lungs with an A-profile, in that one of the following is almost always seen: thickened pleural line, presence of the PLAPS, or a single BLUE-point showing a B-line.
This leads the researchers to recommend that when LUS is being carried out to diagnose COVID-19, a more comprehensive approach should be used. They recommend the 12-region protocol, which covers more of the lung than the current study’s BLUE-protocol.
Another option is to use a local B-line pattern or pleural line thickening as an indication of disease. They propose that this type of interpretation will become more necessary in the emergency setting, in which patients may not show pleural thickening or abnormalities of the PLAPS point. If these are set as criteria, many patients might be missed.
Another research aim was to find a possible correlation between the BLUE-profile and clinical parameters like the P/F ratio and lung compliance. The failure to find any correlation could be due to several factors. For one, the 12-region protocol is more comprehensive but leaves out a significant portion of the back of the lung regions.
Secondly, LUS is capable of assessing only the superficial part of the lung parenchyma, in contrast to the in-depth examination possible with CT scanning. This is especially important with “H” and also “L” type lungs, which present with deep and subpleural involvement, respectively.
The latter could also have a high LUS score because of the widespread subpleural ground-glass pattern, which is present as a B-line pattern on LUS, but almost normal compliance. However, there is a weak correlation between LUS-score and dynamic compliance.
Is Lung Ultrasound Useful in COVID-19?
The study concludes, “Lung ultrasound seems to be a valuable alternative for CT in diagnosing and monitoring SARS CoV-2 pneumonia.”
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
- Haaksma, M. E. (2020). Lung ultrasound findings in patients with novel SARS-CoV2. medRxiv preprint. doi: https://doi.org/10.1101/2020.05.18.20105775. https://www.medrxiv.org/content/10.1101/2020.05.18.20105775v1