Intensive Care Unit (ICU) is a specialised ecosystem in a hospital focusing on the critically ill. As our understanding of ICU survivorship has evolved, a common, yet often missed, serious entity has come to limelight, i.e., ICU Delirium. The term “delirium” has often been used, rather liberally, in clinical settings to describe a patient with altered mental status. However, its diagnosis requires specific features to be present.

ICD 10 has characterised delirium as an organic mental disorder under F05 (delirium not induced by alcohol or psychoactive substances) and is defined by the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) as a reduced ability to direct, focus, sustain, and shift attention. However it is time consuming and also presence of an experienced psychiatrist is a prerequisite to using such complex criteria and have for a long time been a hurdle in identification of the disease. A variety of bed side screening tools, therefore, have been developed and validated, for clinical use by a wide range of personnel ranging from nursing staff to intensivists. These include scoring systems like Confusion Assessment Method for the ICU (CAM-ICU) and Intensive Care Delirium Screening Checklist (ICDSC).

The incidence of this vicious disease, in hospitalised patients of course depends upon immense array of factors including patient population studied and screening methods used resulting in colossal differences in incidences reported by various studies. Overall incidence of delirium has been reported to be between 16-89% of all hospitalised patients with the disease burden in ICU settings pegged to be between 20-80% with rates much higher in mechanically ventilated patients.

Variation in incidence has also been seen across its three motor subtypes—hyperactive, hypoactive, and mixed. A study in a medical ICU has reported mixed and hypoactive delirium to be the most prevalent at a rate of 54.9% and 43.5% respectively, of all delirious patients. Despite such a high rate of prevalence in the ICU, delirium often goes unrecognized by clinicians.

In a medical ICU setting, delirium is reported to be associated with increased risk of complications like self extubation, removal of catheters, prolonged hospital stay, and increased health care costs.  Delirium in general is considered to be associated with  high mortality as well. Furthermore, among the various subtypes of delirium, studies in both ICU and non-ICU patients have suggested that hypoactive delirium is associated with poorer prognosis.

With absence of any well-defined pathophysiology, studying the risk factors has been a monumental task. Grossly, the risk factors for delirium can be present before admission to the ICU, which are known as predisposing factors (are difficult to alter), or develop during the course of the illness itself and are called precipitating factors. Precipitating factors, usually a direct or indirect result of the illness or due to therapeutic interventions, represent areas of risk that are potentially modifiable by preventive or therapeutic strategy.