Encephalopathy is a common complication of systemic illness or direct brain injury. It can manifest as a spectrum that begins with subtle cognitive changes, progresses as a full-blown syndrome of brain dysfunction, and eventually leads to coma or brain death (the latter two are described in separate chapters). In this chapter, we focus on the detection, etiologic diagnosis, and management of noncomatose, critically ill, encephalopathic patients. Their condition has been traditionally known with several interchangeable names such as acute confusional state, acute organic brain syndrome, and acute cerebral insufficiency, but is most commonly referred to as delirium.

Delirium contributes significantly to lengthened hospital stay, increased morbidity and mortality, increased overall medical costs, and worse long-term neurocognitive outcomes. Despite the awareness of its existence since the earliest historical medical documents, timely detection, workup, and appropriate management continue to present challenges for the treating physicians. Delirious patients in the Intensive Care Unit (ICU) form a particularly understudied population with unique characteristics.

1. ▪ Delirium has been described as an acute alteration of consciousness and higher cognitive functions.

2. ▪ It typically develops over a short period of time and has a fluctuating course.

3. ▪ It is a well-defined syndrome that may be precipitated by several diverse pathological processes.

4. ▪ The current edition of the Diagnostic and Statistic Manual (DSM-IV TR) lists criteria for the diagnosis of delirium due to a general medical condition (Table 17.1).

The incidence of delirium has been estimated as between 5% and 40% for hospitalized patients in general and between 11% and 80% for critically ill patients.