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Patients on mechanical ventilation for severe COVID-19 pneumonia had similar mortality rates to patients with other forms of severe pneumonia, but those with COVID tended to be kept on ventilation longer, findings from a large health system showed.

Among more than 1,800 mechanically ventilated patients with severe pneumonia, unadjusted analyses showed higher in-hospital mortality in the group with COVID-19, yet propensity score-matching ultimately revealed no differences between groups (40% vs 38%; OR 1.04, 95% CI 0.81-1.35, P=0.85), according to William Checkley, MD, PhD, of Johns Hopkins University in Baltimore, and colleagues.

In the unadjusted analysis, COVID patients had a lower rate of liberation from mechanical ventilation, a finding that held up in the fully-matched model, which accounted for differences in a host of clinical characteristics as well as risk factors for COVID-19 mortality (subdistribution HR 0.81, 95% CI 0.65-1.00).

"Early in the pandemic, it was suggested that respiratory failure due to COVID-19 may exhibit a different physiologic phenotype and higher mortality compared with non-COVID-19 AHRF [acute hypoxemic respiratory failure]," Checkley and colleagues explained in . "This suggestion and a few small studies comparing respiratory failure due to COVID-19 and non-COVID-19 pneumonia led some clinicians to propose using nonstandard mechanical ventilation strategies."

In their new study, patients in the matched groups also had similar respiratory system compliance and ventilatory ratio.

"Proponents of COVID-19 AHRF as a unique respiratory physiology phenotype suggest that strict adherence to low tidal volume ventilation may not be necessary and may even be harmful," wrote Checkley and coauthors. "However, if COVID-19 pneumonia leads to physiology typical of classic acute respiratory distress syndrome (ARDS), then evidence-based ARDS treatment strategies, such as low tidal volume ventilation and prone positioning, are the only interventions proven to reduce mortality."

Prior studies comparing COVID and non-COVID pneumonia had various limitations, the team noted, including small sample sizes and methods of comparison that allowed for a high risk of confounding, leading to the current study, which was designed "to better inform this debate."

Using electronic health record data, the researchers examined the outcomes of 1,846 adults with pneumonia that needed mechanical ventilation within the first 2 weeks of their hospitalization at the Johns Hopkins Healthcare System, including 719 with COVID-19 pneumonia and 1,127 with non-COVID-19 pneumonia.

Before matching, patients were of similar age (62 vs 61 years), while those in the COVID-19 group were more likely to be male (62% vs 52%), have a higher body mass index (mean 32 vs 30), and were more likely to be from a minoritized group (64% vs 41%). Diabetes was more common in the COVID group, as was a lower Sequential Organ Failure Assessment (SOFA) score, and lower mean PaO₂/FiO₂ ratio. Chronic obstructive pulmonary disease (COPD) and heart disease were more common in the non-COVID group.

Before matching, patients with COVID-19 pneumonia had a longer median time to discharge than patients with non-COVID-19 pneumonia (25 vs 14 days), and among patients discharged alive, those with COVID-19 spent twice as long on mechanical ventilation (10 vs 5 days).

Along with the differences in mortality and lower rate of liberation from mechanical ventilation, unadjusted analyses also showed lower static respiratory system compliance in the COVID-19 group on the first day of mechanical ventilation (32.0 vs 28.4 mL/kg PBW/cm H₂O; P<0.001), with smaller differences on subsequent days.

After propensity-score matching, certain differences in baseline characteristics remained: patients in the COVID-19 group were less likely to have COPD and more likely to have diabetes, immunosuppression, and chronic kidney disease. Patients with COVID-19 pneumonia were also more likely to have a lower white blood cell count and to have received prior high-flow nasal cannula at hospital admission, while non-invasive mechanical ventilation was less common in this group.

After matching, COVID and non-COVID patients had similar static respiratory system compliance (mean difference 1.82 mL/cm H₂O, 95% CI -1.53 to 5.17, P=0.28) and similar ventilatory ratios over the first week of ventilation (mean difference -0.05, 95% CI -0.22 to 0.11, P=0.52).

While ultimately not statistically significant, severe COVID-19 pneumonia patients were found to be discharged from the hospital at 90 days at a lower rate than their non-COVID-19 severe pneumonia counterparts (subdistribution HR 0.83, 95% CI 0.68-1.01).

The study findings "add to the growing evidence that mortality for mechanically ventilated patients with COVID-19 is similar to that of patients with other pneumonias," Checkley and colleagues concluded. "We did not find convincing evidence of different physiologic phenotypes in patients with COVID-19 pneumonia. We caution that deviating from current evidence-based practices (until there are robust data indicating why, how, and when) risks harm."

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