A proposed division of COVID-19 acute respiratory distress syndrome (ARDS) into two types requiring different ventilation approaches found no support from a proof-of-concept study.
The division proposes two subphenotypes of COVID-19 pneumonia based on lung physiology and radiographic findings:
- Typical cases, dubbed “H type,” with high elastance, high shunt, and high lung weight that may benefit from lower tidal volumes and higher positive end-expiratory pressure (PEEP)
- Atypical “L type” ARDS with low elastance, low shunt, and low lung weight that might be better treated by higher tidal volumes and lower PEEP
However, in a study aiming to test the underlying assumptions of this classification, respiratory system compliance (elastance) didn’t correlate with consolidation on chest CT scans indicating poorly or non-aerated lung tissue (regression coefficient +0.13% per mL/cmH2O, P=0.39).
The 79% of patients with a non-focal lung morphology had significantly more parenchymal involvement but not lower compliance than those with focal lung morphology.
“Most patients could not be classified as either ‘H’ or ‘L’ subphenotype, but showed mixed features,” Lieuwe Bos, MD, PhD, of the University of Amsterdam, and colleagues reported in the Annals of the American Thoracic Society.
Robert Dickson, MD, of the University of Michigan School of Medicine in Ann Arbor, called the findings a convincing argument against the coherence of the two phenotypes classification.
“There are now about a half-dozen studies reporting lung physiology in COVID patients who are receiving mechanical ventilation, and none of them support the existence of discrete ‘phenotypes’ of lung injury,” he told MedPage Today. “Physiologically, mechanically ventilated COVID patients are extremely similar to patients with ARDS caused by other causes. At this point, I’d be very skeptical of any claims regarding phenotypes of COVID patients until someone publishes data to support their existence.”
Case series from Italy, Seattle, Boston, and New York have found compliance in COVID-19 is not unusually high, failing to confirm that part of the hypothesis, noted C. Corey Hardin, MD, PhD, of Massachusetts General Hospital in Boston.
“In short, there is no published evidence in support of the ‘L’ and ‘H’ subtypes. Continued discussion of these proposed subtypes is simply a refusal to engage with new data,” said Hardin, who leads Massachusetts General Hospital’s Fast Literature Assessment and Review team, which advocated “bedside measurement and titration of ventilator setting based on individually measured mechanics” rather than using the subphenotypes.
The ultimate test would be head-to-head comparison of subphenotype-directed treatment versus standard of care in a randomized controlled trial, Bos’ group noted. But meanwhile, “an evidence-based approach extrapolating data from ARDS not related to COVID19 is the most reasonable approach for ICU care,” they wrote.
Their retrospective analysis included the first 70 patients with suspected COVID-19 admitted to a single ICU, for which chest CT was routine. Those CT images were available for 38 patients with proven COVID-19, “as the other patients were transferred from other hospitals to our ICU or previously had a CT-scan which supported the diagnosis COVID-19 pneumonia.”
Study limitations included the small sample size, absence of quantitative CT analysis, and lack of formal evaluation of recruitability by performing CT imaging at different PEEP levels.
However, Bos and colleagues noted that “the semi-quantitive evaluation of CT-images at one single level of PEEP is not even available for most clinicians caring for COVID-19 patients and that most physicians, therefore, will resort to using Crs [respiratory system compliance] when these subphenotypes were to be applied in clinical practice.”
Source: MedicalNewsToday.com
