The terms intensive care unit (ICU) syndrome and ICU psychosis have been used interchangeably to describe a cluster of psychiatric symptoms that are unique to the ICU environment. It is often postulated that aspects of the ICU, such as sleep deprivation and sensory overload or monotony, are causes of the syndrome. This article reviews the empirical support for these propositions. We conclude that ICU syndrome does not differ from delirium and that ICU syndrome is caused exclusively by organic stressors on the central nervous system. We argue further that the term ICU syndrome is dangerous because it impedes standardized communication and research and may reduce the vigilance necessary to promptly investigate and reverse the medical cause of the delirium. Directions for future research are suggested.

Numerous authors have noted a cluster of psychiatric signs and symptoms that may occur in patients who are treated in an intensive care unit (ICU) or high-dependency ward and have termed this syndrome ICU psychosis, postoperative delirium, and ICU syndrome; when patients have undergone heart surgery, it has been called postcardiotomy delirium or cardiac psychosis. Frequently, this syndrome is assumed to be peculiar to ICUs.

The aims of this article are to review the etiology and nature of this syndrome and then to discuss the implications of this review for nosology and management. Is there actually a psychiatric syndrome that is attributable to some feature of the ICU experience, or is this "syndrome" most accurately and most helpfully classified as a delirium? We argue that the latter is true and that it is possible and preferable to describe the disorder using established medical nomenclature. Appropriate classification will help to demystify the concept, ensure that crucial organic causes are sought and found, indicate optimal management, and facilitate standardized research.