In order to better determine which therapy is best for patiënts which present with organ falure during the course of their stay in the intesive care unit (ICU) , one has to determine which underlying mechanism is causing this organ falure. We will determine levels of so called "biomarkers" for ferroptosis (a mechan ism of iron-related cell death) in the peripheral blood and biological fluids of criticaly ill patients admitted to the ICU with a catastrrophy (severe infection, trauma ...) . Why ? If it turns out that this ferroptosis plays a role in the ocurrence of organ failure in the critially ill, this will lead to new therapies in the future as drugs become more and more available which can influene this biochemical "pahway". of iron-relatd death.

Inclusion Criteria:

• Admitted to the ICU of UZA
• Critically ill and predicted to be hospitalised in the ICU for > 48 hours (i.e. mostly patients admitted for sepsis, trauma, haemorrhagic shock, neurological catastrophe … which means at risk to develop mono-or multiple organ failure)
• With arterial line in place (for blood sampling)

Exclusion Criteria:

• Refusal of consent by patient or closest relative
• Postoperative patients after major surgery in whom prolonged ICU stay is not foreseen (i.e. elective cardiac surgery