Definition: Sudden severe confusional state due to physical or mental illness. Impaired attention/speed/clarity/coherence of thought. Synonyms: Delirium, acute confusional state, toxic-metabolic encephalopathy.

DSM 5 (five criteria): A. Disturbance in attention & awareness. B. Develops over hours to days, represents acute change from baseline, & tends to fluctuate in severity during the course of a day. C. Additional disturbance in cognition (e.g., memory, orientation, language, visuospatial ability, or perception). D. Disturbances in criteria A & C not better explained by pre-existing/evolving neurocognitive d/o & do not occur in context of severely reduced arousal such as coma. E. Evidence (Hx, exam or lab findings) that disturbance is due to another medical condition, substance intoxication or withdrawal, or exposure to a toxin, or to multiple etiologies.

Mechanism: Pathophysiology largely uncharacterized. ↑ GABAergic & dopaminergic activity &/or central cholinergic deficiency may play roles. Management is empirical.

Risk factors: Advanced age (>80 yo) & one or more of the following: high severity of clinical/surgical illness, dementia, use of sedative medications, visual impairment, dehydration, postoperative, severe pain, anemia.

Triggers: Exposure to noxious insults or precipitants in vulnerable patients. Seemingly benign insult (e.g., sedation) may cause delirium in vulnerable pt. Healthy people usu require multiple insults (e.g., gen anesthesia, major sx, psychoactive drugs, long ICU stay). Therefore, multicomponent approaches are most effective.

Presentation: Most common inpatient behavioral disorder (30% elderly medical pts, 10%-50% elderly surgical pts, up to 80% of ICU patients). Two main forms: Hypoactive & agitated; may also present as a mix. Hypoactive: Inattention, disordered thinking, & ↓ level of consciousness. Agitated: ↑ vigilance, psychomotor & autonomic overactivity; agitation, excitement, tremulousness, hallucinations, delusions. Variations: Hyperactivity w/↑ sympathetic activity, sleep Δs, emotional Δs (e.g., fear, depression, euphoria, perplexity). Elderly: Usu quiet, withdrawn, hypoactive (often underdiagnosed or mistaken for depression).

WORKUP: (1) Recognition of delirium, (2) identification of cause.

General examination: VS, hydration, infectious foci, e/o COPD, jaundice, hepatic failure, stigmata of renal failure, needle tracks, or cherry red lips (e/o CO poisoning). Breath: Alcohol, fetor hepaticus, uremic fetor, or ketones. Bitten tongue and/or fx/dislocation of shoulder (r/o sz). Autonomic si/sx (tachycardia, sweating, flushing, dilated pupils).

Neurologic examination: Level of consciousness & attention. Look for focal signs, multifocal myoclonus, asterixis, & postural action tremor. Loss of VOR or nystagmus w/unexplained ocular palsies sparing pupillary reactivity raises possibility of Wernicke encephalopathy.

Bedside tests of attention: Month of year backward. Digit span: Repeat series of random numbers. Abnl: Inability to repeat >5. Vigilance “A” test: Read 30 random letters. Pt taps on “A”. Abnl: Miss >2.

MONITORING: Two recommended tools, esp. in ICU: the Confusion Assessment Method for ICU (CAM_ICU), or Intensive Care Delirium Screening Checklist (ICDSC).

(Inouye SK, et al. Lancet 2014;383:911.)