Chest dual-energy CT to assess the effects of steroids on lung function in severe COVID-19 patients

Abstract

Background Steroids have been shown to reduce inflammation, hypoxic pulmonary vasoconstriction (HPV) and lung edema. Based on evidence from clinical trials, steroids are widely used in severe COVID-19. However, the effects of steroids on pulmonary gas volume and blood volume in this group of patients are unexplored. Objective Profiting by dual-energy computed tomography (DECT), we investigated the relationship between the use of steroids in COVID-19 and distribution of blood volume as an index of impaired HPV. We also investigated whether the use of steroids influences lung weight, as index of lung edema, and how it affects gas distribution. Methods Severe COVID-19 patients included in a single-center prospective observational study at the intensive care unit at Uppsala University Hospital who had undergone DECT were enrolled in the current study. Patients’ cohort was divided into two groups depending on the administration of steroids. From each patient’s DECT, 20 gas volume maps and the corresponding 20 blood volume maps, evenly distributed along the cranial–caudal axis, were analyzed. As a proxy for HPV, pulmonary blood volume distribution was analyzed in both the whole lung and the hypoinflated areas. Total lung weight, index of lung edema, was estimated. Results Sixty patients were analyzed, whereof 43 received steroids. Patients not exposed to steroids showed a more extensive non-perfused area (19% vs 13%, p < 0.01) and less homogeneous pulmonary blood volume of hypoinflated areas (kurtosis: 1.91 vs 2.69, p < 0.01), suggesting a preserved HPV compared to patients treated with steroids. Moreover, patients exposed to steroids showed a significantly lower lung weight (953 gr vs 1140 gr, p = 0.01). A reduction in alveolar–arterial difference of oxygen followed the treatment with steroids (322 ± 106 mmHg at admission vs 267 ± 99 mmHg at DECT, p = 0.04). Conclusions The use of steroids might cause impaired HPV and might reduce lung edema in severe COVID-19. This is consistent with previous findings in other diseases. Moreover, a reduced lung weight, as index of decreased lung edema, and a more homogeneous distribution of gas within the lung were shown in patients treated with steroids. Trial registration: Clinical Trials ID: NCT04316884, Registered March 13, 2020.

Causes of Hypoxemia in COVID-19 Acute Respiratory Distress Syndrome: A Combined Multiple Inert Gas Elimination Technique and Dual-energy Computed Tomography Study

“…34 At the time of writing, its quantitative analysis has been performed only by a few centers. 35,36 The techniques used to evaluate the distribution of tissue and blood volume, despite small differences, are all variations of the original voxel quantitative analysis of a "traditional" CT scan. 9 Regarding the distribution of the blood volume, it is key to understand whether hypoxic pulmonary vasoconstriction is preserved or lost.…”

“…9 Regarding the distribution of the blood volume, it is key to understand whether hypoxic pulmonary vasoconstriction is preserved or lost. [34][35][36] In both healthy and diseased lungs, hypoxic pulmonary vasoconstriction diverges the blood flow away from the gasless tissue, helping maintain the matching between ventilation and perfusion. 37 The tissue mass followed the expected distribution of ARDS lungs, with proportionally more tissue in the nonaerated regions.…”

Body mass index is associated with pulmonary gas and blood distribution mismatch in COVID-19 acute respiratory failure. A physiological study

“…Each histogram bin was expressed both as the absolute number of voxels as well as as a percentage of the total number of voxels. Based on the HU distribution profiles, each voxel was respectively defined as hyperinflated, normoinflated, poorly inflated, or noninflated ( Gattinoni et al, 2001 ), and as non-perfused (≤0 HU) or perfused (>0 HU) ( Uhrig et al, 2015 ; Ball et al, 2021 ; Perchiazzi et al, 2022 ).…”