Hypoxaemia related to COVID-19: vascular and perfusion abnormalities on dual-energy CT

Abstract

Studies have shown that some patients with coronavirus disease 2019 (COVID-19) and acute hypoxaemic respiratory failure have preserved lung compliance, suggesting that processes other than alveolar damage might be involved in hypoxaemia related to COVID-19 pneumonia.1Gattinoni L Coppola S Cressoni M Busana M Rossi S Chiumello D Covid-19 does not lead to a “typical” acute respiratory distress syndrome.Am J Respir Crit Care Med. 2020; (published online March 30.)DOI:10.1164/rccm.202003-0817LECrossref Scopus (838) Google Scholar The typical imaging features of COVID-19 pneumonia, including peripheral ground-glass opacities with or without consolidation, are also non-specific and can be seen in many other diseases.2Bernheim A Mei X Huang M et al.Chest CT findings in coronavirus disease-19 (COVID-19): relationship to duration of infection.Radiology. 2020; (published online Feb 20.)DOI:10.1148/radiol.2020200463Crossref Scopus (1588) Google Scholar There has been increasing attention on microvascular thrombi as a possible explanation for the severe hypoxaemia related to COVID-19.3Klok FA Kruip MJHA van der Meer NJM et al.Incidence of thrombotic complications in critically ill ICU patients with COVID-19.Thromb Res. 2020; (published online April 10.)DOI:10.1016/j.thromres.2020.04.013Google Scholar, 4Zhou F Yu T Du R et al.Clinical course and risk factors for mortality of adult inpatients with COVID-19 in Wuhan, China: a retrospective cohort study.Lancet. 2020; 395: 1054-1062Summary Full Text Full Text PDF PubMed Scopus (15774) Google Scholar Dual-energy CT imaging can be used to characterise lung perfusion and is done as part of the standard protocol for imaging pulmonary embolism at our institution. Three patients with COVID-19, as confirmed by nasopharyngeal RT-PCR at our hospital, who did not have a history of smoking, asthma, chronic obstructive pulmonary disease, or other pulmonary conditions, underwent dual-energy CT imaging for elevated concentrations of D-dimer (>1000 ng/mL) and clinical suspicion of pulmonary emboli. Although no pulmonary emboli were observed in these individuals, we noted striking perfusion abnormalities that have not been previously described; in retrospect, at least nine other COVID-19 cases also shared these findings. In addition to the typical CT features of COVID-19 pneumonia,2Bernheim A Mei X Huang M et al.Chest CT findings in coronavirus disease-19 (COVID-19): relationship to duration of infection.Radiology. 2020; (published online Feb 20.)DOI:10.1148/radiol.2020200463Crossref Scopus (1588) Google Scholar we observed considerable proximal and distal pulmonary vessel dilatation and tortuosity, predominately within, or surrounding, areas of lung opacities. Here, we present the first published images from dual-energy CT imaging of COVID-19 pneumonia that show profound vascular and perfusion abnormalities (figure; appendix). Three major findings from dual-energy CT were observed on the images of pulmonary blood volume perfusion: preferentially increased perfusion of the lungs proximal to areas of lung opacity, decreased areas of peripheral perfusion corresponding to peripheral lung opacities, and a halo of increased perfusion surrounding peripheral areas of consolidation. The observed pulmonary vascular dilation might be due to relative failure of normal, physiological hypoxic pulmonary vasoconstriction in the setting of overactivation of a regional vasodilatation cascade as part of a dysfunctional and diffuse inflammatory process. Additionally, the mosaic perfusion pattern did not correspond to findings of bronchial wall thickening or secretions, making airway disease as the main underlying cause of hypoxaemia unlikely. Therefore, these perfusion abnormalities, combined with the pulmonary vascular dilation we observed, are suggestive of intrapulmonary shunting toward areas where gas exchange is impaired, resulting in a worsening ventilation–perfusion mismatch and clinical hypoxia. Although peripheral opacities with hypoperfusion can be seen in pulmonary infarction, no pulmonary emboli were observed in any of the studies, and segmental increased perfusion to areas of infarction would be very atypical. Furthermore, a peripheral halo of increased perfusion has not been described in pulmonary infarction, but has been described once previously in a case of bacterial pneumonia.5Otrakji A Digumarthy SR Lo Gullo R Flores EJ Shepard JA Kalra MK Dual-energy CT: spectrum of thoracic abnormalities.Radiographics. 2016; 36: 38-52Crossref PubMed Scopus (67) Google Scholar However, blood and sputum cultures were negative in the three patients with COVID-19 at our hospital and did not suggest bacterial coinfection. It might be possible that the inflammatory response to COVID-19 resembles more of a bacterial infection than a viral infection. Overall, the combination of these imaging findings is novel for COVID-19 pneumonia. Treatment for acute respiratory failure in patients with COVID-19 is challenging in part because of little understanding of the underlying pathophysiology. Our findings are atypical for acute respiratory distress syndrome or thrombotic vascular disease and point to a possible central role for previously underappreciated pulmonary vascular shunting. More detailed assessments of vascular and perfusion changes in patients with COVID-19 are urgently needed. BPL reports royalties from Elsevier as a textbook author and editor, outside the submitted work. AW reports personal fees from Bayer Pharmaceuticals, outside the submitted work. All other authors declare no competing interests. Download .pdf (.16 MB) Help with pdf files Supplementary appendix