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

Deep phenotyping of pulmonary edema and pulmonary vascular permeability in COVID-19 ARDS

Clinical monitoring of pulmonary edema due to vascular hyperpermeability in acute respiratory distress syndrome (ARDS) poses significant clinical challenges. Presently, no biological or radiological markers are available for quantifying pulmonary edema. Our aim was to phenotype pulmonary edema and pulmonary vascular permeability in patients with coronavirus disease 2019 (COVID-19) ARDS. Transpulmonary thermodilution measurements were conducted in 65 patients with COVID-19 ARDS on the day of intubation to determine the extravascular lung water index (EVLWi) and pulmonary vascular permeability index (PVPi). In parallel, ventilatory parameters, clinical outcomes, the volume of lung opacity measured by chest computed tomography (CT), radiographic assessment of lung edema (RALE) score by chest radiography, and plasma proteomics (358 unique proteins) were compared between tertiles based on the EVLWi and PVPi. Regression models were used to associate EVLWi and PVPi with plasma, radiological, and clinical parameters. Computational pathway analysis was performed on significant plasma proteins in the regression models. Patients with the highest EVLWi values at intubation exhibited poorer oxygenation parameters and more days on the ventilator. Extravascular lung water strongly correlated with the total volume of opacity observed on CT (r = 0.72, P < 0.001), whereas the PVPi had weaker associations with clinical and radiological parameters. Extravascular lung water did not correlate with the RALE score (r = 0.15, P = 0.33). Plasma protein concentrations demonstrated a stronger correlation with PVPi than with EVLWi. The highest tertile of PVPi was associated with proteins linked to the acute phase response (cytokine and chemokine signaling) and extracellular matrix turnover. In the clinical setting of COVID-19 ARDS, pulmonary edema (EVLWi) can be accurately quantified through chest CT and parallels deterioration in ventilatory parameters and clinical outcomes. Vascular permeability (PVPi) is strongly reflected by inflammatory plasma proteins.NEW & NOTEWORTHY This study is unique in that it phenotypes pulmonary edema in COVID-19 ARDS using various clinical parameters and biomarkers. First, there is a noteworthy tipping point in the amount of pulmonary edema at which ventilatory and clinical parameters deteriorate. Second, chest CT gives a good approximation of the amount of pulmonary edema. Finally, pulmonary vascular permeability is strongly reflected by inflammatory plasma proteins.