Several medical definitions of delirium exist (including those in the DSM and ICD-10), but the core features remain the same. In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5) with the following criteria for diagnosis:
A. Disturbance in attention and awareness. This is a required symptom and involves easy distraction, inability to maintain attentional focus, and varying levels of alertness. B. Onset is acute (from hours to days), representing a change from baseline mentation with fluctuations throughout the day
C. At least one additional cognitive disturbance (in memory, orientation, language, visuospatial ability, or perception)
D. The disturbances (criteria A and C) are not better explained by another neurocognitive disorder
E. There is evidence that the disturbances above are a "direct physiological consequence" of another medical condition, substance intoxication or withdrawal, toxin, or various combinations of causes

Signs and symptoms
Delirium exists as a stage of consciousness somewhere in the spectrum between normal awakeness/alertness and coma. While requiring an acute disturbance in consciousness/attention and cognition, delirium is a syndrome encompassing an array of neuropsychiatric symptoms.The range of clinical features include: poor attention/vigilance (100%), memory impairment (64–100%), clouding of consciousness (45–100%), disorientation (43–100%), acute onset (93%), disorganized thinking/thought disorder (59–95%), diffuse cognitive impairment (77%), language disorder (41–93%), sleep disturbance (25–96%), mood lability (43–63%), psychomotor changes (e.g. hyperactive, hypoactive, mixed) (38–55%), delusions (18–68%), and perceptual change/hallucinations (17–55%). These various features of delirium are further described below:

Inattention: As a required symptom to diagnose delirium, this is characterized by distractibility and an inability to shift and/or sustain attention.
The benefits of hydration reminders and education on risk factors and care homes solutions for reducing delirium is still uncertain. Treatment
Delirium is a reversible impairment, however, people that are ill with delirium may need to be treated in order to prevent injury and poor outcomes.Treatment of delirium requires attention to multiple domains including: identify and treat the underlying medical disorder or cause(s), optimize physiology, optimize conditions for brain recovery, detect and manage distress and behavioral disturbances, maintaining mobility, provide rehabilitation through cognitive engagement and mobilization, communicate effectively with the patient and their carers, and provide adequate follow-up including consideration of possible dementia and post-traumatic stress. This involves optimizing oxygenation, hydration, nutrition, electrolytes/metabolites, comfort, mobilization, pain control, mental stress, therapeutic medication levels, and addressing any other possible predisposing and precipitating factors that might be disrupting brain function. Multidomain interventions
These interventions are the first steps in managing acute delirium and there are many overlaps with delirium preventative strategies. In addition to treating immediate life-threatening causes of delirium (e.g. low O2, low blood pressure, low glucose, dehydration), interventions include optimizing the hospital environment by reducing ambient noise, providing proper lighting, offering pain relief, promoting healthy sleep-wake cycles, and minimizing room changes. Although multicomponent care and comprehensive geriatric care are more specialized for a person experiencing delirium, several studies have been unable to find evidence showing they reduce the duration of delirium.Family, friends, and other caregivers can offer frequent reassurance, tactile and verbal orientation, cognitive stimulation (e.g. regular visits, familiar objects, clocks, calendars, etc.