Most COVID-19-Related ARDS Does Not Fit Neatly Into Subphenotypes

By Will Boggs MD

May 22, 2020

NEW YORK (Reuters Health) - Most cases of COVID-19-related acute respiratory distress syndrome (ARDS) show features of both typical and atypical subphenotypes, according to a retrospective analysis.

"We should treat patients with ventilator settings that we know are beneficial for patients with acute respiratory distress syndrome, which includes small tidal volumes and prone positioning," Dr. Lieuwe D. J. Bos of UMC Amsterdam, in the Netherlands, told Reuters Health by email. "We should be cautious to change our management based on premature phenotyping of patients, as this might harm some patients more than it benefits others."

Some have proposed subdividing ARDS into typical ARDS ("H type," with high elastance, high shunt, and high lung weight) and atypical ARDS ("L type," with low elastance, low shunt, and low lung weight), subphenotypes that might require different ventilator strategies.

Dr. Bos and colleagues hypothesized that patients with a low elastance (i.e., high respiratory system compliance, Crs) would also show little consolidation on chest CT scan images and that patients with a high elastance (i.e., low Crs) would show considerable consolidation on such images.

To test their hypothesis, they analyzed chest CT scan images in 38 patients with proven COVID-19 admitted to their intensive-care unit (ICU), including 17 patients (45%) with high elastance/low Crs.

They found no relation between Crs and poorly or non-aerated lung tissue, they report in the Annals of the American Thoracic Society.

Most patients had nonfocal lung morphology, with more parenchymal involvement but not a lower Crs compared with patients having focal lung morphology.

Most patients, therefore, could not be classified as either "H" or "L" subphenotype, but instead showed mixed features.

"Such nonfocal lung morphology has been shown to respond favorably to opening of lung tissue with higher pressures and might suggest that higher pressures could be beneficial in some patients, when prone positioning . . . does not result in adequate oxygen levels in the blood," Dr. Bos said.

"We need data-driven approaches to evaluate the existence of treatable traits to improve patient-tailored care," the authors conclude. "Until these data become available, an evidence-based approach extrapolating data from ARDS not related to COVID-19 is the most reasonable approach for ICU care."

SOURCE: Annals of the American Thoracic Society, online May 12, 2020.