Measurements will include the incidence of delirium assessed using the Confusion Assessment Method (CAM). The severity of symptoms will by characterised by the Mini Mental Score and clock drawing. Further measurements will include the prescribed doses of rescue medication, the length of stay on intensive care and in hospital, the time of extracorporeal circulation, and laboratory parameters such as CRP, albumin, lymphocyte count, vitamin B12 and folic acid levels. Side effects of rivastigmine will be quantified.