Impaired Respiratory Function Post COVID-19 Associated With ICU Treatment

Impairments in respiratory function and exercise capacity are common post COVID-19 pneumonia, especially among those who required intensive care unit (ICU) treatment, according to study findings published in BMJ Open Respiratory Research.

Investigators assessed the relationship between COVID-19 illness severity and dyspnea, exercise capacity, spirometry results, and gas exchange measures after disease recovery among adult patients in Iceland who tested positive for SARS-CoV-2 from February 2020 to April 2021.

All COVID-19 survivors with an oxygen saturation level of at least 94% who were discharged to independent living were offered a clinical follow-up visit focused on respiratory care. During the follow-up, the participants underwent the 6-minute walk test (6MWT), spirometry and diffusion capacity of carbon monoxide (DLCO) measurement, and a computed tomography (CT) scan of the chest without an intravenous contrast agent.

The analysis included 164 patients who were categorized by treatment level they had required when infected with COVID-19: 32 had never been admitted to hospital; 103 were admitted to hospital but not the ICU; and 29 had been in the ICU. Their mean age was 60 years, and 45% were female. Most were admitted to a general hospital ward (63%), 18% were admitted to an ICU, and about 20% required ambulatory follow-up only. A majority of participants (74%) had an imaging abnormality at follow-up (CT score of >0), with a median score of 5 (interquartile range [IQR], 0-10).

Participants in the 3 different treatment level groups showed significant differences in the percentage of predicted distance on 6MWT (P = .0003), the FVC percentage (P = .016), FEV₁/FVC ratio (P = .01), the DLCO percentage of predicted (P = 5×10⁻⁶), and oxygen saturation after the 6MWT (P = .003), but not for the percentage of predicted FEV₁ (P = .53).

Investigators also performed regression analyses to determine the association between treatment levels and pulmonary outcomes. The researchers found that patients receiving ICU treatment had shorter 6MWT distance (β = −14% of predicted, P =.0001) and lower DLCO (β = −20% of predicted, P <.0001) than patients receiving ambulatory care. Intensive care treatment also was associated with decreased oxygen saturation after 6MWT (β = −2.1% of predicted, P =.004).

In regression analyses of associations between CT severity scores at follow-up (with a higher severity score indicating greater anatomic involvement from disease) and pulmonary outcomes, the researchers found that higher follow-up CT scores were associated with decreased distance in the 6MWT (β per point in CT score = −0.82% of predicted, P <.0001), FVC decrease (β = −0.46% of predicted, P =.02), an increase in FEV₁/FVC ratio (β = 0.26%, P =.04), a decrease in DLCO (β = −1.1% of predicted, P <.0001), and decreased oxygen saturation after 6MWT (β = −0.11%, P =.004), regardless of modeling method. CT scores were not associated with dyspnea, which was measured using the modified Medical Research Council (mMRC) scale.

Study limitations include: (1) some associations, including those of mMRC score with treatment levels and FEV₁/FVC with imaging changes, barely met the threshold for statistical significance; (2) possible residual confounding; (3) respiratory symptoms were estimated with the mMRC scale; (4) some changes may have resulted from reverse causation; and (5) some data were obtained from unvaccinated participants before the emergence of viral variants.

“Respiratory-focused follow-up for survivors COVID-19 pneumonia should be aimed at survivors of the most severe illness and those with extensive long-term radiologic changes,” the researchers concluded.