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  1. ICU delirium is a common form of acute “brain failure” that is associated with significant morbidity and mortality. Delirium has a dose response relationship with poor outcomes: the longer the delirium duration, the poorer the outcome.

  2. Delirium can be missed in up to 75% of patients if a screening tool is not used, likely because of the high prevalence of hypoactive delirium.

  3. Early diagnosis of delirium is imperative for effective delivery of delirium reduction strategies. Therefore, delirium assessments should be part of the ICU admission physical exam and should be incorporated into the daily work-flow.

  4. ICU-acquired risk factors for delirium (eg, oversedation, immobilization, uncontrolled pain) are potentially modifiable and closely interrelated. Implementation of nonpharmacologic multicomponent strategies to prevent and reduce delirium on an ICU-wide scale (eg, targeted light/no sedation, early rehabilitation) can shorten the duration of ICU delirium and improve clinical outcomes.

  5. Pharmacologic prevention and treatment of delirium (eg, dexmedetomidine over benzodiazepines for sedation) can be considered for individual patients, although the efficacy of these strategies is still unclear.


Delirium is the most common form of acute brain injury in critically ill patients and is associated with potentially long-lasting serious consequences. This chapter reviews the essentials of diagnosis, risk factors, prevention, and treatment of ICU delirium.


Delirium is a disturbance of consciousness and cognition that develops acutely (ie, hours to days), fluctuates over time, and is generally reversible.1 It is characterized by an acute change or fluctuation in baseline mental status, inattention, and either disorganized thinking or an altered level of consciousness. ICU delirium is the most common form of acute brain dysfunction in critically ill patients, with estimates of incidences ranging from 20% to 50% in nonventilated patients and 60% to 80% in ventilated ICU patients, depending on the diagnostic criteria used and the patient characteristics.2,3,4,5,6 It is important to recognize that delirium is not a normal part of critical illness, but rather represents an acute organ failure that is associated with profound short- and long-term consequences.


While the pathophysiology of delirium is still poorly understood, it is thought to be a disease-driven process caused by the complex interaction of various factors including (1) the underlying disease itself, (2) predisposing risk factors unique to each patient, and (3) environmental and treatment-related factors.

Neurotransmitter Imbalance

Delirium is hypothesized to be caused by imbalances in neurotransmitters due to factors such as systemic inflammation, metabolic derangements, acute stress responses, and exposure to psychoactive medications.7 The 2 main neurotransmitters implicated in these derangements are dopamine and acetylcholine, and they work in opposition by increasing and decreasing neuronal excitability, respectively. Other neurotransmitters that have been implicated in the pathogenesis of delirium include g-aminobutyric acid (GABA), serotonin, glutamate, and endorphins. At ...

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