Why do old people in the icu go crazy?

Multiple factors : This is called ICU psychosis or is sometimes called sun downing. In the ICU patient are often very sick , combined with lack of sleep due to their condition and treatment result in the confusion that is seen in the icu. As patient recover and are transitioned to a regular room or home they usually will return to their baseline.

Can happen: Especially people with dementia are prone to what is called ICU psychosis. These people are sick and confined to a small room with all the alarms around them with nurses coming in and out--- they become confused agitated in a totally unfamiliar surroundings.

Delirium: It is not just old people, although they are at higher risk. Patients with critical illness commonly have delirium, this is a brain malfunction which can range from confusion/agitation to coma. In the ICU there are multiple causes. These include toxins that can be present from impaired organ function in the ICU , (like kidney failure) , side effect of needed drugs, or consequence of infections.

Not just old people: Severe illness, sleep disturbances and sedative medications used in icu's can all contribute to delirium. It is a major dilemma for health care providers and research into the ideal sedative agents is ongoing.