Evidence lacking for ARDS subphenotypes in COVID-19

A new analysis published in the Annals of the American Thoracic Society was unable to definitively identify two distinct subphenotypes of COVID-19-related acute respiratory distress syndrome.

In the study, Lieuwe D.J. Bos, MD, PhD, from the department of intensive care and the department of respiratory medicine at the University Medical Center Amsterdam and the laboratory of experimental intensive care and anesthesiology at the Academic Medical Center of the University of Amsterdam, and colleagues noted that some researchers have postulated that patients with COVID-19 can develop typical or atypical ARDS. Typical presentation has been referred to as “H type” and is characterized by high elastance, high shunt and high lung weight, and atypical presentation has been referred to as “L type” and is characterized by low elastance, low shunt and low lung weight.

“Alike for the abovementioned morphological subphenotyping, some have speculated these subphenotypes require different ventilator strategies. Patients with ‘H type’ ARDS may benefit from lower tidal volumes and higher positive end-expiratory pressure, and patients with ‘L type’ ARDS may benefit from higher tidal volumes and lower positive end-expiratory pressure,” they wrote.

To validate these subphenotypes, the researchers conducted a retrospective analysis of 38 patients with COVID-19 who had chest CT scans performed after intubation and before transport to the ICU at the Academic Medical Center of the University of Amsterdam. Bos and colleagues hypothesized that patients with a low elastance or high respiratory system compliance would show little consolidation on chest CT scans, whereas patients with high elastance or low respiratory system compliance would show more consolidation on chest CT scans.

Overall, there were 17 patients with respiratory compliance below 40 mL/cmH₂O and seven with minor parenchymal involvement, with results revealing no significant association between respiratory compliance and poorly or nonaerated lung tissue. The researchers also identified 30 patients with a nonfocal lung morphology. Although more parenchymal involvement was noted in these patients (P = .0065), they did not have lower respiratory compliance than those with focal lung morphology (P = .72), according to the data.

“Our finding was that most patients do not fulfill the criteria of one phenotype or the other. I do not feel encouraged to spilt patients into the two proposed phenotypes to guide ventilator management, but rather treat patients with the uniform, high-quality care that we always deliver to patients with lung injury,” Bos said in a press release.

“The presented data are the first independent test of proposed subphenotypes of

COVID19-related ARDS and highlight that features of the H and L subphenotypes are not mutually exclusive. Simultaneously, we validated the existence of heterogeneity in lung morphology known from non-COVID-19-related ARDS,” the researchers wrote. “We need data-driven approaches to evaluate the existence of treatable traits to improve patient-tailored care. 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.”