Intensive care unit psychosis: A disorder in which patients in an intensive care unit (ICU) or a similar hospital setting may experience anxiety, become paranoid, hear voices, see things that are not there, become severely disoriented in time and place, become very agitated, even violent, etc. The condition has been formally defined as "acute brain syndrome involving impaired intellectual functioning which occurs in patients who are being treated within a critical care unit." ICU psychosis is a form of delirium, or acute brain failure. Organic factors including dehydration, hypoxia (low blood oxygen), heart failure (inadequate cardiac output), infection and drugs can cause or contribute to delirium.

The treatment of ICU psychosis depends on the cause(s). Family members, familiar objects and calm words may help. Dehydration should call for fluids. Heart failure needs treatment with digitalis. Infections must be diagnosed and treated. Sedation with anti- psychotics agents may help.

To prevent ICU psychosis, many critical care units now have instituted visiting hours, they try to minimize shift changes in the nursing staff caring for a patient, the lighting is coordinated with the normal day-night cycle, etc. ICU psychosis usually goes away when the patient leaves the ICU.

One patient in every 3 who spends more than 5 days in an ICU experiences some form of psychotic reaction, according to current estimates. As the number of intensive care units and the number of people in them grow, ICU psychosis is perforce increasing as a problem.

What causes ICU psychosis is not fully known. Something about the ICU causes some people, who are already experiencing great debility, stress and pain, to "lose their minds." Among the factors which are believed to play into ICU psychosis are:

• Sensory deprivation (being put in a room often without windows, away from family, friends and all that is familiar),
• Sensory overload (being tethered to noisy machines day and night),
• Pain (which may not be adequately controlled in an ICU),
• Sleep deprivation,
• Disruption of the normal day-night rhythm, or simply
• The loss of control over their lives that patients often feel in an ICU.

ICU psychosis often goes away with the coming of morning or sleep. Although it may linger through the day, severe agitation usually occurs only at night. (This phenomenon, called sundowning, is common in nursing homes).