Haemostasis and immunothrombosis in extracorporeal circuits
File(s)
Author(s)
Lee, Teresa Mei Ling
Type
Thesis or dissertation
Abstract
ARDS is a debilitating condition within intensive care with high morbidity and mortality. ECMO can be used to support patients with severe ARDS in whom conventional management such as invasive mechanical ventilation and prone positioning has failed. The main complications from ECMO use remain haemostatic with bleeding and thrombosis despite advances in biomaterials and ECMO anticoagulation guidelines. COVID-19 highlighted the importance of immunothrombosis in patients with ARDS. Neutrophil extracellular traps (NETs) and platelet-leucocyte interactions are an increasing area of interest in sepsis and ECMO.
The first aspect of this thesis investigated the presence of immunothrombosis in patients with COVID-19 and non-COVID-19 ARDS who required ECMO. Incidence of ECMO circuit thrombosis was higher in COVID-19 patients which was related to duration of ECMO rather than COVID-19, indicating ECMO itself is immunothrombotic. COVID-19 patients had lower D-dimer levels in the lead up to circuit thrombosis suggesting a different mechanism for thrombosis e.g. reduced fibrinolysis. This highlights the difficulty in predicting circuit thrombosis with current clinical biomarkers. Biomarkers of neutrophil activation and NETosis in patient samples demonstrated increased NETosis after ECMO initiation despite already high levels of neutrophil and platelet activation. The reduced platelet aggregation during ECMO which improved after ECMO discontinuation suggesting ECMO increases NETosis and platelet dysfunction, and may be related in ECMO immunothrombosis.
The second aspect of this thesis describes the development of flow cytometry protocols to measure leucocyte-platelet interactions by measuring leucocyte-platelet aggregates (LPA) using the ibidi microfluidics chamber to generate LPA formation under flow conditions. This model demonstrated that LPA form more readily with platelet activation compared to leucocyte activation and can be reduced using a platelet inhibitor. This model can be adapted for use with isolated cells, and endothelial cell providing a platform to investigate the effects of flow on neutrophil and platelet activation, and leucocyte-platelet interactions.
The first aspect of this thesis investigated the presence of immunothrombosis in patients with COVID-19 and non-COVID-19 ARDS who required ECMO. Incidence of ECMO circuit thrombosis was higher in COVID-19 patients which was related to duration of ECMO rather than COVID-19, indicating ECMO itself is immunothrombotic. COVID-19 patients had lower D-dimer levels in the lead up to circuit thrombosis suggesting a different mechanism for thrombosis e.g. reduced fibrinolysis. This highlights the difficulty in predicting circuit thrombosis with current clinical biomarkers. Biomarkers of neutrophil activation and NETosis in patient samples demonstrated increased NETosis after ECMO initiation despite already high levels of neutrophil and platelet activation. The reduced platelet aggregation during ECMO which improved after ECMO discontinuation suggesting ECMO increases NETosis and platelet dysfunction, and may be related in ECMO immunothrombosis.
The second aspect of this thesis describes the development of flow cytometry protocols to measure leucocyte-platelet interactions by measuring leucocyte-platelet aggregates (LPA) using the ibidi microfluidics chamber to generate LPA formation under flow conditions. This model demonstrated that LPA form more readily with platelet activation compared to leucocyte activation and can be reduced using a platelet inhibitor. This model can be adapted for use with isolated cells, and endothelial cell providing a platform to investigate the effects of flow on neutrophil and platelet activation, and leucocyte-platelet interactions.
Version
Open Access
Date Issued
2025-07-03
Date Awarded
2026-09-01
Copyright Statement
Attribution-Non Commercial-No Derivatives 4.0 International Licence (CC BY-NC-ND)
Advisor
Patel, Brijesh
O'Dea, Kieran
Mumby, Sharon
Publisher Department
Department of Surgery & Cancer
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)