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The research program explores how delirium influenced brain function in patients surviving delirium and septic encephalopathy from a non neurological specialized ICU cohort from 2013 to 2015 in Rigshospitalet (Glostrup).

The overall aim is to understand the pathophysiological mechanism in delirium and septic encephalopathy and its consequences.

For this purpose we will:

1. Provide extensive cognitive testing. These results provide the basis for categorization of patients surviving septic encephalopathy and delirious patients.
2. First, the investigators will examine if the differences in cognitive function is reflected in the ability of the brain to generate high-frequency electrical oscillations that accompany and underlie perception, attention, cognition, memory formation and retrieval. It will be performed by carrying out continuous EEG (cEEG) and by examination of steady-state evoked cognitive EEG responses.
3. Second, the investigations will examine MRI, structural and diffusion tensor imaging sequences. Hippocampal, thalamic, amygdala, lentiform nucleus and cingulate cortex volumes will be determined bilaterally and will be compared between individuals with healthy brain aging and patients that survived delirium.
4. Third, the investigators will assess plasma markers of free radical production.

Inclusion Criteria for the ICU cohort:

• Age >18 years;
• Length of stay >24 hours in the ICU.

Exclusion Criteria for the ICU cohort:

• Expected death <24 hours;
• Psychiatric illness; pre-existing delirium; severe dementia; cerebrovascular event \

Survivors of the critical ill cohort which were included the ones without known acute central nervous system affection admitted to a medical ICU with sepsis or septic shock, mono- or multi organ failure (respiratory insufficiency, circulatory shock, hepatic and/or renal failure) as indicated by a need for invasive or non-invasive mechanical ventilation, vasoactive drugs and/or CRR)

EEG, cognitive tests and MRI could be available for other researchers in the field.