Rationale: There is large heterogeneity in disease states of critically ill patients at ICU admittance and there is also large heterogeneity in their disease severity during ICU stay. Still, some patients may show remarkable similarities in disease patterns. There is a lack of understanding of causal mechanisms that lead to divergent outcomes in critically ill patients, and at the same time different diseases may share common underlying, yet unidentified, causal pathways that could explain similarities between different diseases.

Objective: To explore the association between patient characteristics and the severity of organ failure in critically ill patients admitted to the ICU Study design: Prospective cohort study Study population: Adult critically ill patients in the ICU Intervention (if applicable): not applicable Main study parameters/endpoints: Maximum severity of organ failure observed during ICU stay measured by the maximum SOFA score and quality of life at one year follow-up

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: \

Inclusion Criteria:

• Adults Definition: age ≥18 years.
• Emergency admission to the ICU Definition: patients who are acutely admitted to the ICU due to acute or unexpected critical illness, either from the emergency department or the ward or transferred from an ICU (or a ward) from another hospital.

Exclusion Criteria:

• Planned admission
• Absence of an invasive arterial or venous line for blood sampling.
• Any continued cardiopulmonary resuscitation efforts upon admission which limit access to the patient for research activities.
• Main ICU admission reason chronic (non-invasive) home ventilation
• Main ICU admission reason normothermic treatment after cardiac arrest
• Main ICU admission reason ischemic stroke, intracerebral bleeding, or isolated neurotrauma
• Main ICU admission reason Coronavirus Disease 2019 (COVID-19)
• Solid organ or hematopoietic stem cell transplant during current hospital admission
• Strict isolation due to any contagious disease
• No informed consent

All patients acutely admitted to the ICU