ICU delirium

ICU delirium is an acute, fluctuating disturbance of attention, awareness, and cognition that occurs in critically ill patients, often developing over hours to days. It is a form of acute brain dysfunction and is a common complication in the ICU, particularly among mechanically ventilated patients.

The pathophysiology of ICU delirium is multifactorial and incompletely understood. Proposed mechanisms include neuroinflammation, impaired neurotransmitter signaling (cholinergic deficiency and dopamine excess), oxidative stress, and disruption of the blood-brain barrier. These processes may be precipitated by systemic illness, sedative medications, or metabolic derangements, leading to acute brain dysfunction.

In the ICU setting, the prevalence of delirium in adults is estimated at 31%, with incidence varying between 4-11% depending on motor subtype. Delirium is particularly common in mechanically ventilated ICU patients, with prevalence rates reaching up to 75%. On general medical inpatient units, the overall occurrence rate is approximately 23%. Among older adults, 11-25% present with delirium on admission, and an additional 29-31% develop it during hospitalization. Postoperative delirium increases with surgical complexity, ranging from 7% to 51% in patients undergoing cardiovascular surgery. Delirium also occurs in non-hospital settings, with probable cases reported in 19% of older adults attending memory clinics, and prevalence in palliative care populations ranging from 4% to 88% depending on care setting and stage of illness.

Major risk factors include advanced age, preexisting cognitive impairment, hypertension, or alcohol use disorder, severity of illness, mechanical ventilation, use of sedative or analgesic medications (especially benzodiazepines), metabolic disturbances, infection, and prolonged ICU stay. Modifiable risk factors include sleep disruption, immobility, and polypharmacy. Coma is an independent risk factor for the development of delirium in the ICU.

Delirium typically develops acutely and can fluctuate in severity throughout the day. It presents in hyperactive, hypoactive, or mixed subtypes, with hypoactive delirium often underrecognized despite its poor prognosis. Delirium may last for days or weeks and is associated with prolonged mechanical ventilation, increased ICU and hospital stay, long-term cognitive decline, and increased risk of death.

ICU delirium is associated with poor short- and long-term outcomes. It independently predicts prolonged mechanical ventilation, longer ICU and hospital stays, increased healthcare costs, and a greater risk of in-hospital mortality. Delirium increases the risk of death by 38%, and in postoperative patients, the 30-day mortality rate may reach up to 10%, compared to 1% in those without delirium. Long-term consequences include persistent cognitive impairment, functional decline, and increased risk of institutionalization. The duration of delirium correlates with the severity of long-term cognitive deficits. Positive delirium screening in critically ill adults is strongly associated with cognitive impairment at 3 and 12 months after ICU discharge and may be associated with longer hospital stays. However, delirium has not been consistently associated with PTSD, post-ICU psychological distress, depression, or long-term functional dependence. Evidence on its association with ICU length of stay, discharge disposition, or mortality is mixed. Notably, rapidly reversible delirium is associated with outcomes similar to those of patients who do not develop delirium.