Delirium in Critical Illness

Delirium is an acute, fluctuating disturbance of attention and awareness that is common in critically ill patients and is associated with worse outcomes, including longer hospital stays, higher mortality and long-term cognitive impairment. In the ICU it is often missed, particularly in its hypoactive form, which is why systematic screening with validated tools is emphasised.

Definition

Delirium is an acute and fluctuating disturbance of attention, awareness and cognition that develops over a short period and represents a change from baseline; in critical illness it is frequently provoked by acute illness, medications and the ICU environment.

Scope

This topic covers ICU delirium as a clinical syndrome: its definition and subtypes, its detection with validated bedside tools such as the CAM-ICU, its risk factors and prognostic significance, and its place within the broader management of sedation and analgesia. It is a reference overview and does not provide diagnostic or treatment instructions for an individual patient.

Key concepts

• Acute disturbance of attention and awareness
• Fluctuating course
• Hyperactive, hypoactive and mixed subtypes
• Routine screening with validated tools (e.g. CAM-ICU)
• Modifiable risk factors (e.g. sedatives, immobility)
• Association with mortality and long-term cognitive impairment
• Non-pharmacological prevention within the ABCDEF bundle

Clinical relevance

Delirium signals acute brain dysfunction and is linked to worse short- and long-term outcomes, so recognising and screening for it is a core part of critical care. Guidelines emphasise routine assessment and addressing modifiable contributors (for example minimising deliriogenic sedation and promoting early mobility); this entry summarises that evidence for orientation and is not a basis for individual diagnosis or treatment.

Epidemiology

Delirium affects a large proportion of mechanically ventilated and other critically ill patients during their ICU stay, the hypoactive form being easily overlooked. Ely et al. (2004) showed that ICU delirium independently predicts higher mortality, underscoring its prognostic importance.

Evidence & guidelines

The CAM-ICU (Ely et al., 2001) provided a validated bedside method to detect delirium in ventilated patients. The 2018 PADIS guidelines (Devlin et al.) recommend routine delirium monitoring and emphasise non-pharmacological prevention over routine pharmacological treatment, and the ICU Liberation/ABCDEF bundle evaluation (Pun et al., 2019) linked bundle adherence to less delirium and better survival.

History

Acute confusion in the critically ill was long regarded as an expected, transient nuisance ('ICU psychosis'). Validated detection tools in the early 2000s (notably the CAM-ICU) and cohort evidence linking delirium to mortality and long-term cognitive impairment reframed it as a serious, monitorable form of acute brain dysfunction, central to the 2013 and 2018 SCCM guidelines.

Debates

Should ICU delirium be treated pharmacologically?

Despite widespread use of antipsychotics, trial evidence has not shown that routine pharmacological treatment shortens delirium or improves outcomes, so guidelines emphasise prevention and addressing modifiable causes over routine drug treatment.

Key figures

• E. Wesley Ely
• Sharon Inouye
• Pratik Pandharipande
• John Devlin

Seminal works

• ely-2001-camicu
• ely-2004-mortality
• devlin-2018

Frequently asked questions

Why is hypoactive delirium easy to miss?

Hypoactive delirium presents as quiet withdrawal and reduced responsiveness rather than agitation, so without systematic screening it is frequently mistaken for sedation or fatigue.

How is delirium detected in the ICU?

Validated bedside tools such as the Confusion Assessment Method for the ICU (CAM-ICU) allow structured screening for delirium even in non-verbal, ventilated patients.