Rationale: Delirium is highly prevalent in the ICU. It may cause significant morbidity and mortality. One of the factors that may provoke a delirium is the use of GABA-ergic anaesthetics. Recent studies have shown that sedation with alpha-2-adrenergic agonists may lead to a reduction of the total amount of GABA-ergic anaesthetics and reduction of delirium. In clinical practice the alpha-2-adrenergic agent clonidine is used as an add-on sedative in mechanically ventilated patients who suffer from delirium, but there are no large studies proving that this therapy is effective and safe.