# Endothelial Activation and Permeability in Patients on VV-ECMO Support: An Exploratory Study

## TL;DR

This study explores how VV-ECMO affects endothelial cells in patients with severe COVID-19, finding increased endothelial activation and damage over time.

## Contribution

The study is the first to longitudinally assess endothelial activation and permeability in VV-ECMO-treated patients with COVID-19.

## Key findings

- Endothelial activation markers like ICAM-1 and angiopoietin-2 increased over time during VV-ECMO.
- In vitro experiments showed that patient plasma induced pulmonary endothelial hyperpermeability.
- Non-survivors had higher angiopoietin-2 levels, suggesting a link to poor outcomes.

## Abstract

Background Veno-venous extracorporeal membrane oxygenation (VV-ECMO) supports critically ill patients with respiratory failure. However, ECMO may induce systemic inflammation, hemolysis, and hemodilution, potentially resulting in endothelial activation and damage. Therefore, this study explored the longitudinal changes in circulating markers of inflammation, hemolysis, and endothelial activation and damage in patients with COVID-19 on VV-ECMO. Methods Plasma was obtained before, within 48 h as well as on day 4, week 1, and week 2 of ECMO support and after decannulation. Circulating markers were measured using Luminex, ELISA, and spectrophotometry. Human pulmonary endothelial cells were exposed to patient plasma, and in vitro endothelial permeability was assessed using electric cell-substrate impedance sensing. Results From April 2020 to January 2022, plasma was collected from 14 patients (71.4% male; age 54 (45–61) years). IL-6 levels decreased (1.238 vs. 0.614 ng/mL, p = 0.039) while ICAM-1 increased (667 vs. 884 ng/mL, p = 0.003) over time when compared to pre-ECMO. Angiopoietin-1 decreased after ECMO initiation (7.57 vs. 3.58 ng/mL, p = 0.030), whereas angiopoietin-2 increased (5.20 vs. 10.19 ng/mL, p = 0.017), particularly in non-survivors of ECMO. Cell-free hemoglobin decreased directly after VV-ECMO initiation but remained stable thereafter (55.29 vs. 9.19 mg/dL, p = 0.017). Moreover, the plasma obtained at several time points during the ECMO run induced in vitro pulmonary endothelial hyperpermeability. Conclusions This exploratory study shows that patients on VV-ECMO support due to COVID-ARDS exhibit progressive endothelial activation and damage but not inflammation and hemolysis. Larger prospective studies are necessary to elucidate pathophysiological pathways leading to endothelial activation and damage, thereby reducing organ failure in these critically ill patients.