Can Ultrasonography Accurately Diagnose ARDS?

By Marilynn Larkin

September 24, 2019

NEW YORK (Reuters Health) - Ultrasonography (US) allows for bedside detection of acute respiratory disease syndrome (ARDS) without radiation and should be more widely used, researchers in Italy suggest.

Experts in the U.S. are not convinced, however.

Dr. Davide Chiumello of the University of Milan and colleagues conducted a single-center study of 32 sedated, paralyzed ARDS patients (62.5% men) with a mean age of 65, mean BMI of 25.9, and mean Pao2/Fio2 of 139.

Computed tomography (CT) and lung US were performed at a positive end-expiratory pressure of 5 cm H2O. A standardized assessment of six regions per hemithorax was used; each region was classified for the presence of normal aeration, alveolar-interstitial syndrome, consolidation, and pleural effusion.

The team calculated agreement between the two techniques and assessed diagnostic variables for US using CT as a reference.

As reported online August 26 in Critical Care Medicine, global agreement between lung US and CT ranged from 0.640 to 0.934, and was 0.775 on average.

Overall, US sensitivity ranged from 82.7% to 92.3% and specificity, from 90.2% to 98.6%. Results were similar with regional analysis.

US diagnostic accuracy was significantly higher when morphologic patterns not reaching the pleural surface were excluded, with areas under the receiver operating characteristic curve of 0.854 versus 0.903 for alveolar-interstitial syndrome, and 0.851 versus 0.896 for consolidation.

"Lung ultrasound is a reproducible, sensitive, and specific tool, which allows for bedside detections of the morphologic patterns in acute respiratory distress syndrome," the authors state. "The presence of deep lung alterations may impact the diagnostic performance of this technique."

Dr. Baskaran Sundaram, Director of Cardiothoracic Imaging at Thomas Jefferson University in Philadelphia, told Reuters Health by email, "(Lung) US has limitations, including poor sound wave penetration through the air in the lungs and rib cage, and operator dependence. Obesity, emphysema, chest wall deformity, lines' drain tubes, and support devices over the patients pose additional challenges."

All patients were in the early phase of ARDS, he noted. In this phase, "the lungs have a significant amount of acute inflammatory exudates which may accentuate the performance of (lung) US. As ARDS evolves, inflammatory exudates subside, and fibrosis ensues, which may negatively influence the performance of (lung) US."

Consolidation (pneumonia and aspiration) caused ARDS in most of the study patients, he said. "The texture of the lungs during these conditions becomes similar to the liver or spleen. There was also a significant amount of patients with pleural effusion." Both of those factors may artificially enhance the performance of US, he noted.

Also, he continued, the CT images were end-exhalation images whereas the US images were obtained in patients in the semi-recumbent, tidal-breathing phase, which would favor US to reveal lung abnormalities.

Further, he added, "the slice thickness of CT in this study is suboptimal, as it is much higher (approximately 5-10 times higher) than the traditional high-resolution lung imaging used for ARDS evaluation."

For these and other reasons, Dr. Sundaram said, "we feel that there is only limited data available to support the role of (lung) US in reliably detecting and managing patients with ARDS. However, the current study findings help to generate hypotheses and design future studies."

Dr. Walter Chua, an attending in pulmonary and critical care medicine and associate program director for the internal medicine residency program at LIJ Forest Hills in Queens, New York said the study results "have to be viewed cautiously."

Like Dr. Sundaram, he noted that this was a small observational study.

"ARDS remains a clinical diagnosis using all the information available to the clinician," he told Reuters Health by email.

"Bedside ultrasound may help, but there are a lot of caveats to take into account, including 1) experience of the operator; 2) image acquisition, as patients can have different characteristics making ultrasound imaging difficult; and 3) standardization of ultrasound findings for diagnosis."

"The authors' level of experience in ultrasound may be much (greater) than many intensivists', and will vary based on where they were trained," he noted. "Right now, official certification for critical care ultrasound is still being ironed out by many clinical groups to determine the proficiency of new graduates. The article is a step forward in helping provide a foundation for aiding in the diagnosis in ARDS but doesn't supplant clinical gestalt."

Dr. Chiumello did not respond to requests for a comment.


Crit Care Med 2019.


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