OBJECTIVES: Prone positioning allows to improve oxygenation and decrease mortality rate in COVID-19–associated acute respiratory distress syndrome (C-ARDS). However, the mechanisms leading to these effects are not fully understood. The aim of this study is to assess the physiologic effects of pronation by the means of CT scan and electrical impedance tomography (EIT). DESIGN: Experimental, physiologic study. SETTING: Patients were enrolled from October 2020 to March 2021 in an Italian dedicated COVID-19 ICU. PATIENTS: Twenty-one intubated patients with moderate or severe C-ARDS. INTERVENTIONS: First, patients were transported to the CT scan facility, and image acquisition was performed in prone, then supine position. Back to the ICU, gas exchange, respiratory mechanics, and ventilation and perfusion EIT-based analysis were provided toward the end of two 30 minutes steps (e.g., in supine, then prone position). MEASUREMENTS AND MAIN RESULTS: Prone position induced recruitment in the dorsal part of the lungs (12.5% ± 8.0%; p < 0.001 from baseline) and derecruitment in the ventral regions (–6.9% ± 5.2%; p < 0.001). These changes led to a global increase in recruitment (6.0% ± 6.7%; p < 0.001). Respiratory system compliance did not change with prone position (45 ± 15 vs 45 ± 18 mL/cm H 2 O in supine and prone position, respectively; p = 0.957) suggesting a decrease in atelectrauma. This hypothesis was supported by the decrease of a time-impedance curve concavity index designed as a surrogate for atelectrauma (1.41 ± 0.16 vs 1.30 ± 0.16; p = 0.001). Dead space measured by EIT was reduced in the ventral regions of the lungs, and the dead-space/shunt ratio decreased significantly (5.1 [2.3–23.4] vs 4.3 [0.7–6.8]; p = 0.035), showing an improvement in ventilation-perfusion matching. CONCLUSIONS: Several changes are associated with prone position in C-ARDS: increased lung recruitment, decreased atelectrauma, and improved ventilation-perfusion matching. These physiologic effects may be associated with more protective ventilation.

Radiological and functional sequelae of Coronavirus Disease 2019 (COVID-19) pneumonia are still poorly understood. This was a prospective, observational, physiological, cohort study on consecutive adult patients with COVID-19 pneumonia admitted in April–May 2020 in the high dependency respiratory unit of L. Sacco University Hospital in Milan (Italy). During hospitalization, patients underwent chest computed tomography (CT), blood gas analysis, spirometry, and lung diffusion capacity for carbon monoxide (DLco), which were repeated 6 weeks post-discharge. Chest CTs were individually read by two expert radiologists, that calculated the total severity score (TSS). Twenty patients completed the study (mean age 58.2 years, 70% males). During the acute phase, mean DLco, alveolar volume (VA), and vital capacity (VC) were 56.0 (16.3), 64.8 (14.0), and 71.7 (16.9) % predicted, respectively, and were inversely associated with PaO2/FiO2 ratio. Fifty percent of patients had a restrictive ventilatory pattern; mean TSS was 7.9 (4.0). At follow up, gas exchange parameters were normalized; consolidations persisted in 10% of cases, while DLco was <80% predicted in 65% of patients and was independently predicted by Log10D-dimer at admission (β −18.675; 95%CI, −28.373–−9.076; p = 0.001). In conclusion, functional abnormalities in COVID-19 pneumonia survivors can persist during follow up and are associated with the severity of the disease.

While lung ultrasonography (LUS) proved to be a useful diagnostic and prognostic tool in acute phase of COVID 19 pneumonia, its role in detecting long-term pulmonary sequelae has yet to be explored. In our prospective observational study we assessed the potential of LUS in detecting the presence of computed tomography (CT) fibrotic-like changes after 6 months from COVID-19 pneumonia. Patients who were discharged with a diagnosis of severe COVID-19 pneumonia were enrolled. After 6 months from hospital discharge they underwent LUS, chest CT scan and pulmonary function tests. A logistic regression analysis was performed to assess the association between presence of symptoms, LUS score and diffusing capacity for carbon monoxide (DLCO) at 6-month after hospital discharge and CT scan fibrotic-like changes. A second logistic model was performed to assess the value of some predefined baseline factors (age, sex, worst PaO2/FiO2, ventilator support, worst CRP value, worst D-dimer value and worst LUS score during hospitalization) to predict fibrotic-like changes on 6-month CT scan. Seventy-four patients were enrolled in the study. Twenty-four (32%) showed lung abnormalities suitable for fibrotic-like changes. At multivariate logistic regression analysis LUS score after 6 months from acute disease was significantly associated with fibrotic-like pattern on CT scan. The second logistic model showed that D-dimer value was the only baseline predictive variable of fibrotic-like changes at multivariate analysis. LUS performed after 6 months from severe COVID-19 pneumonia may be a promising tool for detection and follow-up of pulmonary fibrotic sequelae. Supplementary Information The online version contains supplementary material available at 10.1007/s11739-022-03084-9.