Difficulty in recruiting subjects for the trial.

Nowadays features for the diagnosis of delirium are:

1. Disturbance of consciousness (i.e. reduced clarity of environment awareness) with reduced ability to focus, sustain or shift attention;
2. A change in cognition (such as memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance that is not better accounted for by a pre-existing or evolving dementia;
3. The disturbance develops over a short period of time (usually hours to days) and its severity fluctuates during the course of the day;
4. There is evidence from the history, physical examination, or laboratory findings that the disorder is caused by the direct physiological consequences of a general medical condition, substance intoxication or substance withdrawal.

Treatment of underlying clinical disease is important to remit the delirium. However, these procedures alone are not enough to remit the delirium early and to prevent sequels. There is a need for a specific and faster strategy to treat the delirium.

The investigators want to test the hypothesis that an Anticholinesterase Inhibitor (donepezil) can reduce the duration of the delirium.

Inclusion Criteria:

• Over 60 year old
• Delirium according to the CAM-ICU (Confusion Assessment Method for Intensive Care Unit)
• informed consent (legal representatives)

Exclusion Criteria:

• unable to swallow pills
• previous allergy to donepezil
• Atrioventricular block of 2nd and 3nd degree