For years it has been known that many patients who survive critical illness do not return to their original state of health, resulting in long-term consequences of critical illness. Weakness acquired in the intensive care unit (ICU) is a physical consequence occurring in 25% to 80% of patients who receive mechanical ventilation for more than 4 days and in 50% to 75% of patients with sepsis. Nearly all patients affected with ICU-acquired weakness have symptoms that persist years later. Issues with cognitive function occur in 30% to 80% of ICU survivors and include memory, planning, problem-solving, visual-spatial, and processing problems. Cognitive consequences may improve during the months after discharge. However, 25% of patients with adult respiratory distress syndrome (ARDS) have long-term persistent cognitive impairment 6 years after discharge. In several studies,1-3 survivors of severe sepsis who were more than 65 years of age still had cognitive impairment 8 years after hospital discharge. Anxiety, depression, and sleep disturbances can last from months to years. Survivors also experience post traumatic stress disorder (PTSD) long-term, with an incidence between 10% and 50% and persisting for up to 8 years. Follow-up studies longer than 8 years have not been reported, and for some survivors, these consequences of critical illness may not resolve.

As many as 80% of ICU survivors have some form of cognitive or brain dysfunction, according to the Society of Critical Care Medicine. While receiving intensive care, patients often are heavily sedated and connected to a ventilator. During this time, a temporary brain injury can develop that is linked to later issues with memory and thinking. At the same time, many ICU survivors experience post-traumatic stress symptoms, including depression, prolonged muscle weakness, and fatigue.
Patients who survive sepsis are particularly vulnerable to post-ICU syndrome and about 1.4 million of them suffer from long-term disabilities, according to the Sepsis Alliance. The not-for-profit advocacy group is developing pamphlets on post-sepsis issues for patients, as well as spreading the word on social media websites

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.