POCUS in Determining COVID-19 Severity

By Michael Prats

COVID severity graphic

Comparative study of lung ultrasound and chest computed tomography scan in the assessment of severity of confirmed COVID-19 pneumonia

Intensive Care Med July 2020 - Pubmed Link


Take Home Points

1. In COVID19 patients, the degree of lung ultrasound findings correlates with the severity of disease based on CT.

2. The degree of lung ultrasound findings might correlate with clinical severity, but this study does not show that conclusively.


Background

Its been a while since we talked about ultrasound in COVID-19. As you can see from even a brief visit to our database of articles, there have been countless publications on this topic since we initially reported on the preliminary studies. Many of them are good, but not many of them told us anything new. We know that COVID-19 looks like a viral pneumonia on ultrasound. We know that ultrasound findings correlate with CT findings. The sensitivity and specificity appears to be fairly good compared to CT and PCR testing, and there’s a good chance that ultrasound is more sensitive than chest xray. What remains to be determined is if POCUS can somehow help us in the acute presentation of patients with suspected or confirmed COVID-19. This varies by practice location and resources - it could be anything from screening to diagnosis to prognostication. These authors are interested in predicting the severity of the disease to come. They reference a letter to the editor that provides data that the percentage of lung involved on an initial CT was associated with death or the need for mechanical ventilation within 5 days. Can POCUS help us in determining how sick these patients get?

Check out more on the prior evidence of POCUS for COVID-19 in the Evidence Atlas!


Questions

How does lung ultrasound perform in determining the severity of COVID-19 pneumonia as assessed by a chest CT?

Is a lung ultrasound score associated with clinical outcomes in COVID-19 patients?


Population

Multi-center retrospective, four university hospitals in France.

Evaluated patients in emergency department and intensive care units.


Inclusions:

  • Adult patients

  • Admitted to ED or ICU with confirmed SARS-CoV-2 infection (symptoms + positive PCR)

  • Had to have had both lung ultrasound (LUS) and chest CT (within 24 hours of LUS)

Exclusions:

  • Chest CT performed >24 hours after LUS


Design

Patients received standard history and physical examination, monitoring, vitals signs

Low SpO2/FiO2 ratio was considered <357 (equivalent to PaO2/FiO2 of 300)

LUS performed within first 2 hours after admission.

CT had to be performed within 24 hours of the LUS. Most CTs were non-contrast, low-dose chest CT.


The LUS score (see below) was compared to mild, moderate, and severe pneumonia on CT (as read by a radiologist)

  • Mild was simple and focused ground glass opacities (GGOs) < 10% of lungs total

  • Moderate different lesions (GGOs, crazy paving, consolidation) between 10-50%

  • Severe was more than 50% of pulmonary parenchyma

For analysis - the mild and moderate were combined into a “not severe” group


Primary outcome was the AUC of the LUS compared to CT scan.

Sample size was calculated to be 87 with the assumption that 40% of patients would have severe pneumonia on chest CT.


Who did the ultrasounds?

Emergency physicians or intensivists who were the ones caring for the patient

~40% of these were highly skilled experts

10% were fairly novice but had at least 25 supervised ultrasounds


The Scan

Curvilinear transducer

Curvilinear


12 lung regions - modified so that patient did not have to be turned as much

Looked for:

  • Alveolar consolidation (subpleural echo poor region or one with tissue-like echotexture)

  • Interstitial syndrome (two or more positives regions in the four antero-lateral regions in each lung)

  • Pneumothorax (defined as lack of lung sliding - which we know is not specific)

  • Pleural effusion

  • Pleural irregularity (including small sub-pleural consolidations)


LUS Score (found in supplemental material)

Sum of points from each of the 12 regions. For each region it was assigned a point value:

0 = normal

1 = moderate interstitial syndrome

2 = severe interstitial syndrome (multiple or coalescent B lines)

3 = alveolar consolidation

So scores could range from totally normal (0) or every lung field consolidated (36).


Learn how to do Ultrasound for Viral Pneumonia from 5 Minute Sono!

5minsono


Check out COVID-19 Pathology on the POCUS Atlas!

thePOCUSAtlas


Results

N = 100 patients

  • 77% from the emergency department

  • Many patients excluded because CT was >24 hours after LUS (n = 194)

  • Median age 61

  • 35% female

  • 17% BMI > 30 kg/m

  • There was median of 4 hour delay between LUS and chest CT (IQR 3-7)


Primary Outcome - LUS was significantly associated with CT severity

AUC for LUS compared to CT

0.78 (CI 0.68-0.87)

Minimal CT severity had mean LUS 8 (CI 4-11)

Moderate CT severity had mean LUS 14 (CI 11-16)

Severe CT severity had mean LUS 20 (CI 18-23)


LUS >23 predicted severe SARS-CoV-2 pneumonia on CT → Specificity >90% (actual percentage not listed). This was in 23% of patients.

LUS <13 excluded severe SARS-CoV-2 pneumonia on CT → Sensitivity >90% (actual percentage not listed). This was in 39% of patients.

38% were in the “gray zone” between 13 and 23


Secondary Outcomes

LUS score higher in mechanically ventilated patients (28 vs 14, p <0.01). All mechanically ventilated patients had LUS >19

  • AUC of LUS for mechanical ventilation was 0.92.

LUS score higher in patients with SpO2/FiO2 ratio <357 (19 vs 11, p <0.01).

Lung ultrasound found significantly less bilateral consolidations compared to CT (instead had more “absent consolidations”). Lung ultrasound had more pleural irregularities (32% vs 15% on CT).

Median LUS score was higher in ICU group (21) than in ED (13).


Electronic supplement again has a lot more data beyond what is found in manuscript

Test characteristics of LUS compared to CT for various findings, n = 200 hemithoraces

Interstitial Syndrome

  • Sensitivity 92.2%

  • Specificity 23.8%

Consolidation

  • Sensitivity 34.1%

  • Specificity 84.8%

Pleural Effusion

  • Sensitivity 33.3%

  • Specificity 98.4%

Pleural Irregularity

  • Sensitivity 46.7%

  • Specificity 70.6%


Strengths

Prospective

Multi-center

Clinically oriented research question

Met power analysis

Spectrum of ultrasound operators increases generalizability


Limitations

Retrospective

Practice variability may make primary outcome of correlation with CT less useful for some areas

Did not directly measure association between LUS and patient centered outcomes (such as with regression analysis)

Excluded large number of patients (194 out of otherwise eligible 294) for chest CT >24 hours after LUS exam. While this is important for comparison of CT and LUS, it also could bias the population depending on why there was delay in obtaining that CT.


Discussion

I think the main question here is what do we do with this information? Does this change our management? Obviously, this is largely dependent on how you are currently using lung ultrasound and CT in COVID-19 patients. If you are currently not using ultrasound at all - this paper is not saying that you need to. If you are getting CTs on everybody to determine severity of their disease - this study is saying perhaps you could use ultrasound instead. Does this data really mean that we can use ultrasound to prognosticate outcomes of our patients? Not definitively. It does seem intuitive that patients with more areas of lung ultrasound findings will likely be sicker, but this study is limited by its retrospective nature and the fact that these end points were secondary outcomes.

Very similar study out of France from May 2020 (preprint). Their results were even better showing AUC = 0.93 for normal versus pathologic. 95% sensitivity and 83% specific.


Summary

This is a retrospective multicenter study from 4 EDs and ICUs in France looking at 100 patients with COVID19 pneumonia. They found that a LUS score (which was basically how many zones of lung had lung findings) correlated with the severity based on CT. There were higher scores in patients that were intubated and had poor oxygenation.


Take Home Points

1. In COVID19 patients, the degree of lung ultrasound findings correlates with the severity of disease based on CT.

2. The degree of lung ultrasound findings might correlate with clinical severity, but this study does not show that conclusively.


More Great FOAMed on this Topic

Core Ultrasound - COVID Resources

The POCUS Atlas - Ultrasound in COVID-19

Zedu - COVID-19 POCUS Resources

St Emlyn's - POCUS for COVID-19

SAEM AEUS COVID-19 Ultrasound Resources


Our score

3 Probes


Expert Reviewer for this Post

Soucy

Zachary Soucy, DO, FAAEM @ERDr_Sous

Zach is an Emergency Medicine physician and director of EUS and the EUS fellowship as well as co-chair of the system wide PoCUS committee at Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire. His areas of focus include ultrasound in medical education and system wide PoCUS.


Reviewer's Comments

What a well-timed review of “the COVID-19” as we embark on a third leg of our journey where college students travel from and to hotspots, millions of children go back to school and cold weather brings us all closer to the fireplace (inside). Emergency departments and ICUs throughout the United States are predicted to see a resurgence in COVID-19 shortly. In speaking with colleagues around the country there is no doubt the pandemic has propelled point of care ultrasound (PoCUS) into the fore front of acute care providers minds. Many of us have seen the use of what many considered technology accessory to patient care become a trusted front line tool. “What did the PoCUS show?” from consulting services is far more common now than this time last year. Though I would like to think it is my institutional influence it is undoubtedly more likely to come from the uptick in ultrasound use as we all troubleshoot best ways to isolate, transport, and care for our sick COVID + patients.

In all the chaos of early spring I think this is a good attempt to tease out what we all want to know; can ultrasound replace CT for risk stratification/prognostication? In that attempt this article falls short but does provide evidence, as many recent COVID-19 LUS studies have, that lung PoCUS can be additive to a thorough evaluation.

As is typical of the Ultrasound G.E.L team, the article is well reviewed. Salient points are summarized and limitations noted. The study is also limited to CT comparison without clinical outcomes other than ICU admission. I would have liked to see a more comprehensive patient evaluation to demonstrate clinically what type of patient was assigned to the mild, moderate, and severe CT categories. I whole heartedly agree outcomes measures would further increase our understanding of this population and predicted utility of LUS. I believe the authors comment similarly in one of the final discussion paragraphs.

I was a bit surprised by the low sensitivity for pleural effusion as US is exquisitely sensitive for small effusions leading me to believe the ct read commented on even the smallest of findings. It is possible this caries through with other CT findings as well potentially driving down sensitivity of LUS. Lastly, I would have liked to see a subset analysis of the LUS related to experience. The authors make note to include expert, proficient, and new users and % of the operators they comprise. Taking that a step further to analyze and comment on how user experience influenced US accuracy of LUS findings would have been helpful and possibly given the results some added context. That said with the small n it is possible they could not power the subset analysis.


Cite this post as

Michael Prats. POCUS in Determining COVID-19 Severity. Ultrasound G.E.L. Podcast Blog. Published on September 14, 2020. Accessed on November 30, 2020. Available at https://www.ultrasoundgel.org/98.
Published on 09/14/20 04:00 AM
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