Delirium (Acute Confusion)

Delirium is an acute, fluctuating disturbance of attention and awareness that develops over a short period and represents a change from baseline cognition. It is a common and serious geriatric syndrome, frequently triggered by an acute medical illness, surgery, or medication, and superimposed on underlying vulnerability such as advanced age, dementia, or sensory impairment. Because it signals acute physiological disturbance, delirium is regarded as a marker of acute brain dysfunction in older patients.

Definition

Delirium is an acutely developing, typically fluctuating disturbance of attention and awareness accompanied by additional cognitive change, that is a direct consequence of another medical condition, substance, or multiple causes, and is not better explained by a pre-existing or evolving neurocognitive disorder.

Scope

This topic covers the definition and core features of delirium, its predisposing and precipitating factors, the multifactorial model that distinguishes vulnerability from triggers, motor subtypes, and the structured assessment used to recognize it. It is a reference and educational entry; it does not provide diagnostic protocols or treatment instructions.

Core questions

• What distinguishes delirium from dementia and from other causes of confusion?
• How do predisposing vulnerability and precipitating insults combine to produce delirium?
• What are the core diagnostic features (acute onset, inattention, fluctuation) and the motor subtypes?
• Why is delirium considered both a geriatric syndrome and a marker of acute illness?

Key concepts

• Acute onset and fluctuating course
• Inattention
• Predisposing vs precipitating factors
• Hypoactive, hyperactive, and mixed motor subtypes
• Delirium superimposed on dementia
• Confusion Assessment Method (CAM)
• Multicomponent prevention

Key theories

Predisposing-precipitating (vulnerability) model

Delirium is understood as the product of an interaction between baseline vulnerability (predisposing factors such as age, dementia, and sensory impairment) and acute insults (precipitating factors such as infection, surgery, or medications): a highly vulnerable person may become delirious from a trivial insult, whereas a robust person requires a major one. This model frames delirium as a multifactorial geriatric syndrome and motivates multicomponent prevention.

Mechanisms

Delirium reflects acute, usually reversible disruption of large-scale brain network function rather than a single focal lesion. Multiple converging pathways have been proposed — including neuroinflammation, neurotransmitter imbalance (notably cholinergic deficiency and dopaminergic excess), metabolic and oxidative stress, and disrupted neuronal connectivity — that impair attention and higher-order cognition. The clinical picture emerges when an acute insult acts on a vulnerable brain with reduced reserve, consistent with the predisposing-precipitating model; the same insult may cause no disturbance in a person with greater reserve.

Clinical relevance

Delirium is common in hospitalized older adults, is frequently under-recognized (especially the hypoactive subtype), and is associated with prolonged hospital stay, functional decline, and adverse outcomes. This entry explains how delirium is conceptualized and assessed and how the preventive evidence is organized; it is educational and not a basis for individual diagnosis or treatment.

Epidemiology

Delirium is one of the most common complications of acute illness and hospitalization in older adults, with incidence rising in higher-risk settings such as intensive care and the postoperative period and among people with pre-existing cognitive impairment. It is a strong predictor of poor outcomes and is frequently missed when not actively screened for.

Evidence & guidelines

The Confusion Assessment Method (Inouye and colleagues, 1990) provided a widely used structured approach to recognition. Narrative reviews (Inouye and colleagues, 2014) synthesize the syndrome, mechanistic reviews (Maldonado, 2013) summarize proposed pathways, a multicomponent prevention trial (Inouye and colleagues, 1999) demonstrated that targeting risk factors reduces incidence, and consensus guidance such as the American Geriatrics Society postoperative delirium guideline (2014) summarizes recommendations. These sources frame the field and are not individualized advice here.

History

Acute confusional states have been described since antiquity, but modern geriatric medicine reframed delirium from an incidental feature of illness into a defined, recognizable, and partly preventable syndrome. Operational diagnostic criteria and the Confusion Assessment Method in 1990 made systematic recognition feasible, and the demonstration that multicomponent risk-factor intervention reduces incidence established delirium as a target for prevention.

Debates

How should delirium and dementia be distinguished, especially when superimposed?

Delirium frequently occurs in people with dementia, and separating acute, fluctuating delirium from a stable or progressive dementia — or recognizing delirium superimposed on dementia — remains a central clinical and conceptual challenge.

What is the role of pharmacologic versus non-pharmacologic management?

Multicomponent non-pharmacologic prevention has the strongest support, while the place of medications for established delirium is contested and emphasized chiefly for safety and symptom control rather than cure.

Key figures

• Sharon K. Inouye
• José R. Maldonado
• Rudi G. J. Westendorp
• Jane S. Saczynski

Seminal works

• inouye-1990-cam
• inouye-1999-help
• inouye-2014

Frequently asked questions

How is delirium different from dementia?

Delirium develops acutely over hours to days, fluctuates, and centers on impaired attention, whereas dementia develops gradually over months to years and follows a more stable course; delirium can also occur on top of dementia.

Why is delirium often missed?

The hypoactive form, in which a person becomes quiet, drowsy, and withdrawn, is easily mistaken for fatigue or depression, so delirium is frequently overlooked unless attention is actively assessed with a structured method.