Platelet count reduction during in vitro membrane oxygenation affects platelet activation, neutrophil extracellular trap formation and clot stability, but does not prevent clotting

Introduction:

Due to improved technology and increased application the mortality during extracorporeal membrane oxygenation (ECMO) is constantly declining. Nevertheless, complications including haemorrhage or thrombus formation remain frequent. Local mitigation of coagulation within an ECMO system to prevent thrombus formation on ECMO components and optimizing systemic anticoagulation is an approach to reduce clotting and bleeding complications at once. Foreign surfaces of ECMO systems, activate platelets (PLTs), which besides their major role in coagulation, can trigger the formation of neutrophil extracellular traps (NETs) contributing to robust thrombus formation. The impact of a reduced PLT count on PLT activation and NET formation is of paramount importance and worth investigating.

Methods:

In this study platelet poor (PLT^–) and native (PLT⁺) heparinized human blood was circulated in two identical in vitro test circuits for ECMO devices for 6 hours. PLT reduction was achieved by a centrifugation protocol prior to the experiments. To achieve native coagulation characteristics within the test circuits, the initial heparin dose was antagonized by continuous protamine administration.

Results:

The PLT^– group showed significantly lower platelet activation, basal NET formation and limited clot stability measured via thromboelastometry. Fluorescent and scanning electron microscope imaging showed differences in clot composition. Both groups showed equal clot formation within the circuit.

Conclusions:

This study demonstrated that the reduction of PLTs within an ECMO system is associated with limited PLT activation and NET formation, which reduces clot stability but is not sufficient to inhibit clot formation per se.

In Vitro models for thrombogenicity testing of blood-recirculating medical devices

INTRODUCTION

Blood-recirculating medical devices, such as mechanical circulatory support (MCS), extracorporeal membrane oxygenators (ECMO), and hemodialyzers, are commonly used to treat or improve quality of life in patients with cardiac, pulmonary, and renal failure, respectively. As part of their regulatory approval, guidelines for thrombosis evaluation in pre-clinical development have been established. In vitro testing evaluates a device's potential to produce thrombosis markers in static and dynamic flow loops.

AREAS COVERED

This review focuses on in vitro static and dynamic models to assess thrombosis in blood-recirculating medical devices. A summary of key devices is followed by a review of molecular markers of contact activation. Current thrombosis testing guidance documents, ISO 10993-4, ASTM F-2888, and F-2382 will be discussed, followed by analysis of their application to in vitro testing models.

EXPERT OPINION

In general, researchers have favored in vivo models to thoroughly evaluate thrombosis, limiting in vitro evaluation to hemolysis. In vitro studies are not standardized and it is often difficult to compare studies on similar devices. As blood-recirculating devices have advanced to include wearable and implantable artificial organs, expanded guidelines standardizing in vitro testing are needed to identify the thrombotic potential without excessive use of in vivo resources during pre-clinical development.