This study aims to investigate the impact of platelet concentrate (PC) transfusions on endothelial function and the systemic inflammatory response in thrombopenic patients admitted to intensive care who require prophylactic platelet transfusions.

Endothelial function will be measured using a laser Doppler device coupled with an acetylcholine iontophoresis system that is applied to the skin.

This is a single-centre, non-randomised, non-interventional human research study (RIPH3) investigating the impact of platelet transfusion on endothelial function, endothelial biomarkers, systemic inflammation, oxidative stress and peripheral tissue perfusion. Patients will be recruited during their stay in intensive care, after receiving information and providing their consent (non opposition). Platelet transfusion will be prescribed as part of their treatment. Before the transfusion, at the end of the transfusion and one hour afterwards, a clinical examination will be performed, along with an assessment of tissue perfusion and microcirculatory blood flow measurements using a Doppler laser coupled with iontophoresis. Blood samples will be taken before the transfusion and one hour after its completion to assess the systemic inflammatory response. Participation in this research study will take a maximum of four hours. No specific follow-up is planned for patients included in the study.

Inclusion Criteria:

• Adult patient ≥ 18 years of age
• Admitted to intensive care
• Requires prophylactic platelet transfusion for thrombocytopenia
• Enrolled in a social security program
• No objection to participating in the study

Exclusion Criteria:

• Recent platelet or red blood cell transfusion (< 24 hours)
• Need for urgent red blood cell transfusion due to active bleeding
• Patient under guardianship or conservatorship
• Significant peripheral edema

Any adult admitted to intensive care, regardless of the reason, who has thrombocytopenia and requires prophylactic platelet transfusion