POCUS beats chest x-ray for COVID-19-related pneumonia

By Louise Gagnon, AuntMinnie.com contributing writer

November 5, 2020 -- Point-of-care ultrasound (POCUS) performed better than chest x-ray in diagnosing atypical pneumonia that's presumed to be COVID-19, according to a study presented at the American College of Emergency Physicians (ACEP) annual meeting in late October.

Point-of-care ultrasound had higher sensitivity than chest x-ray for the task, although both modalities fell short in terms of specificity in comparison to CT. Researchers analyzed imaging for diagnosing COVID-19 cases in the early part of the pandemic, when access to polymerase chain reaction (PCR) tests was inconsistent.

"Many places were faced with, especially at the beginning of the pandemic, not having access to the PCR (nasopharyngeal) swabs, with trying to make a diagnosis (of atypical pneumonia/COVID-19) through alternative methods," explained Dr. Kendra Mendez, the study's presenting author and an ultrasound fellow at the Lewis Katz School of Medicine at Temple University in Philadelphia.

Mendez noted the data were collected prospectively over a two-week period in April at Temple University Hospital, which has more than 105,000 visits to the emergency department annually, as it experienced a surge during the pandemic.

"We already use lung ultrasound to differentiate between various conditions, differentiating between heart failure and [chronic obstructive pulmonary disease] exacerbation, for example," Mendez said. "The protocol of using lung ultrasound when someone is in respiratory distress is already in our department. We wanted to see the utility of it with COVID-19."

Some of the advantages of point-of-care ultrasound include portability and decreased burden with respect to infection control, according to Mendez.

"The portable units are much easier to disinfect than our larger machines," she said.

Mendez and co-investigators set up a protocol based on previous research of the appearance of atypical viral pneumonia on ultrasound or x-ray and used it to examine different areas of the lungs, comparing sensitivity and specificity of ultrasound versus chest x-ray. They used noncontrast CT as the gold standard.

They used an eight-zone lung ultrasound protocol and categorized predefined abnormalities as subpleural consolidations, irregular pleural lines, or pleural effusion.

Investigators enrolled 143 patients with signs and symptoms of COVID-19. A total of 70 had both a positive lung ultrasound and positive chest x-ray. Of those, 58 had positive CT findings suggestive of atypical viral pneumonia.

A total of 42 patients had a positive lung ultrasound and negative chest x-ray. Of those, 23 had positive CT findings. Six patients had a negative lung ultrasound and a positive chest x-ray, but none of the six had a positive CT finding. Twenty-five patients had both a negative lung ultrasound and negative chest x-ray. Still, seven of them advanced to CT imaging because they had one or more high-risk features, such as the presence of immunosuppression or lymphopenia. Two of the seven had a positive CT.

Lung ultrasound recorded higher sensitivity than chest x-ray, the researchers found.

Chest x-ray vs. lung ultrasound for COVID-19 detection
  Chest x-ray Lung ultrasound
Sensitivity 69.9% 97.6%
Specificity 44.4% 33.3%

"Lung ultrasound is more sensitive than chest x-ray," said Dr. Mendez. "Both modalities had poor specificity."

The data's generalizability is limited by several variables, such as the fact that the study was performed at a single center, the disease prevalence was 75% in the study population, and the potential lack of familiarity with point-of-care ultrasound in a given emergency department, according to Mendez.

"All emergency medicine physicians in our institution are well-versed in point-of-care ultrasound, possibly limiting the utility (of point-of-care ultrasound) in the broader emergency medicine community," said Dr. Mendez.

Still, point-of-care ultrasound can be a triage tool, particularly in under-resourced settings, Mendez pointed out.


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