Pulmonary process: Hypoxemia, hypercarbia, pneumonia, pulmonary embolism
Cardiac process: Heart failure, heart attack, hypotension, hypertensive encephalopathy
GI process: Bleeding, hepatic encephalopathy
Renal process: Uremia, hypovolemia
Heme-Oncology: Malignancy, including para-neoplastic syndromes, anemia
Infectious process: Infection anywhere; the more frail the patient, the lower magnitude the infxn necessary to cause delirium
Endocrine/Metabolic Rrocess: Hyper/hyponatremia, Hypercalcemia, Hyper/hypoglycemia, Hypo/hyperthyroidism; Vitamin B1 deficiency (Wernickes Encephalopathy)
CNS process: stroke, infection (encephalitis, meningitis, CNS abscess), Wernickes, non-convulsive status, trauma, autoimmune/inflammatory (ADEM, autoimmune encephalitis), other
Multi-system organ dysfunction can contribute
Substances of abuse: Cocaine, crystal meth, amphetamines, PCP, ETOH, canabis, other
Toxic exposures: Carbon monoxide, organophosphates, others
Meds: ADHD meds, dopaminergics, SSRIs, steroids, benzos, narcotics, dilantin, anti-psychotics, other - try to link new med to onset of sx
Withdrawal from alcohol, benzos, narcotics, other combinations of agents
Pain: Severe pain, in particular if coupled w/any of above
Unfavorable environments: Hospitalization, disruption of normal sleep wake cycle, ICU stay, procedures, restraints, foley catheter

Impaired hearing or vision
Prior hx delirium, dementia, hospitalization, surgery or serious illness
Multiple medications, in particular if newly started
Baseline dementia
Impaired ability to clear toxins/meds (e.g. AKI or CKD, liver dysfunction)
Older/more physiologically frail patients require less of a "nudge" to develop delirium as compared w/those who are younger and/or healthier

Acute change from prior behavior, including→ disorganized thinking, impaired short term memory
Inattention, disorientation, confusion, delusions, hallucinations, altered sleep patterns
Hypoactive (75%) or hyperactive (25%)
Symptoms fluctuate, with spectrum from somnolent to very agitated
Typically reversible
Delirium is always secondary to something

Range in level of alertness from agitation to somnolence
May have abnormal vital signs (e.g. tachycardia, bradycardia, hypertension, hypertension, febrile) - based sometimes on underlying process (e.g. infection)
Focus of exam should be search for focal findings that might identify cause (e.g. findings of pneumonia, heart failure, cellulitis/other infection, etc)
Due to age and co-morbidities, PE findings for underlying process may be subtle/atypical

Detailed history: to make the diagnosis, determine how different from baseline (sometimes requires history from a family member/person who knows the patient), substance use/abuse
PE, with attention to VS and search for focal process (e.g. infection)
Medication review (in and out of hospital)
CBC, Chem 7, lfts, TSH, B12, UA/UCx, EKG, CXR
Consider troponins, blood cultures, head CT (if trauma, concern for bleeding, stroke), MRI (to detect more subtle parenchymal disease, inflammatory states), ABG (hypercarbia, hypoxemia, acidosis), EEG (if concern for non-convulsive status), LP (if febrile, headache, confusion and concern for meningitis/encephalitis)

Delirium: Etiologies By Organ System