Approach
The diagnosis of delirium is primarily clinical, requiring frequent observation by caregivers in cases where symptoms are less overt.[57][58] See the Urgent considerations section for conditions requiring immediate management.
Pre-existing patient factors
Much of the diagnostic work-up for delirium involves conducting a careful and thorough history. In most cases, this might require interviewing a family member or friend of the patient. Calls to the pharmacy to review medications can also be invaluable in situations where a patient is unable to contribute to a history. Key pre-existing patient factors include the following issues.[21]
Previous cognitive status: when delirium is considered as a diagnosis, it is first imperative to establish a baseline cognitive and functional status prior to the onset of symptoms. Given that symptoms of delirium are often confused with dementia, it is important to ascertain whether observed changes in mental status occurred acutely (delirium) or have been chronically present (dementia). In most cases, a rough assessment of previous cognitive status can be obtained from the patient's family. A previously obtained assessment of cognition such as a Mini Mental Status Examination (MMSE) or Montreal Cognitive Assessment (MoCA) can be compared with a current screen to determine whether symptoms related to cognitive changes are acute or chronic in nature. The Observational Scale of Level of Arousal (OSLA) is a bedside assessment which has a sensitivity of over 90% and a specificity of over 80% for diagnosing delirium in older patients.[59] UK guidelines recommend that clinicians consider using OSLA to distinguish between dementia and delirium in people who have not been diagnosed with either condition.[60]
The use of delirium screening tools, such as the well-validated Confusion Assessment Method (CAM), the Confusion Assessment Method for the Intensive Care Unit (CAM-ICU), the Intensive Care Delirium Screening Checklist (ICDSC) or the 4AT tool can be instrumental in diagnosing delirium.[3][61][62][63][64] SIGN Decision Support Opens in new window 4AT Rapid Clinical Test for Delirium Opens in new window The 3D-CAM is a 3-minute structured assessment that operationalises the CAM algorithm for ease of delirium recognition at the bedside. It has a high sensitivity and specificity in older medical patients as well as in those with dementia.[65] The 3D-CAM has also been used to assess delirium severity.[66] The Confusion Assessment Method Severity (CAM-S) scoring system has been validated, and demonstrated to be associated with clinical outcomes.[67] Studies have evaluated and validated the use of the CAM-ICU, the brief CAM, and the Delirium Triage Screen (DTS) for use in the emergency department.[8][68][69][70] In a paediatric intensive care unit delirium prevalence was found to be 21% and was detected using the Cornell Assessment of Pediatric Delirium.[71] If a patient is high-risk and confusion is suspected, serial measurements of cognition can help to distinguish delirium from baseline dementia states.[16] Small studies have used both the CAM and CAM-ICU to detect delirium in patients with dementia.[72] The 4AT is a brief tool for delirium detection designed for use in clinical practice. SIGN Decision Support Opens in new window 4AT Rapid Clinical Test for Delirium Opens in new window It incorporates an assessment of alertness, the Abbreviated Mental Test - 4 (AMT4), the Months Backwards test, and measures of acute change or fluctuating course.
Medication usage: when delirium is identified, further history and examination should be directed to identifying and treating the precipitating factors. Given that drugs are implicated in 12% to 39% of all cases of delirium, medication lists should be carefully scrutinised with an eye towards discontinuing or altering potentially high-risk medications whenever possible.[73] Herbal remedies, non-prescription medications, and illicit substances should also be considered in a medication review. The use of anticholinergic drugs such as diphenhydramine bears special mention as they are frequently implicated in delirium and are often found in non-prescription medications (e.g., paracetamol and ibuprofen) deemed safe by patients or family members.[52]
Comorbid conditions: given that delirium is frequently a symptom of commonly encountered medical conditions, a careful review of comorbidities should be conducted with emphasis on neurological diseases (e.g., stroke, Parkinson's disease, dementia), cardiovascular diseases (e.g., myocardial infarction, angina), and a history of renal/metabolic diseases (e.g., hyponatraemia, hypernatraemia, chronic renal failure). In addition, dehydration, constipation, hypoxia, infection, immobility or limited mobility, poor nutrition, and sensory impairment should be addressed, as these can also precipitate delirium.[74] Decreased functional status and dehydration have been shown to be predictive for the development of delirium in older hospitalised patients.[75]
Pain levels: the presence of severe pain is associated with delirium.[16]
Alcohol and drug use: alcohol intoxication and withdrawal are frequently associated with delirium. Recent binge drinking can cause alcoholic ketoacidosis. Benzodiazepine withdrawal might also precipitate delirium.[51][52]
Environmental factors: key issues such as sleep deprivation, multiple procedures, restraint use, and intensive care stay are associated with delirium and might be causative conditions.[16] Tools such as the CAM-ICU and the ICDSC can be helpful in ascertaining delirium in the intensive care unit environment.[76][77][78][79]
Physical examination
Physical examination should be thorough as precipitating insults for delirium might be relatively minor if a patient has numerous risk factors. Important considerations include the following.
Hydration: dehydration should be ruled out as a precipitating factor.
Pupillary response: might suggest drug intoxication, drug withdrawal, or stroke.
Neck stiffness: meningitis or encephalitis should be considered.
Lung examination: decreased breath sounds and rales might indicate infection (e.g., pneumonia) or diseases commonly associated with hypoxia such as CHF and COPD.
Cardiovascular examination: evaluation for physical findings evident with coronary disease or myocardial infarction should be performed.
Abdominal examination: might suggest intra-abdominal infection. Constipation should be ruled out.
Suprapubic tenderness or palpable bladder: might suggest urinary tract infection or obstruction.
Hip tenderness: might suggest occult hip fracture, a frequently missed trigger for delirium in frail older residents, particularly if they are bed bound.
Neurological findings: focal findings might suggest stroke or neurological insult.
Mental state: acute psychosis may be mistaken for delirium. Diagnosis is clinical and is often a diagnosis of exclusion. The DSM-5-TR diagnostic criteria for brief psychotic disorder are: at least one symptom of delusions, hallucinations, or disorganised speech, for more than 24 hours but less than 30 days. Patients may also have grossly disorganised or catatonic behaviour. There may be a history of psychological stressors involved in triggering the episode.[15] Examination findings may include: strange behaviours, unco-operative states, disorganised speech, labile mood, and depression. Patients may have suicidal or homicidal intention.
Investigations
Given the vast differential of delirium, investigations should be guided by history and physical examination findings. In the absence of these, a preliminary work-up in all patients without definitive historical or physical findings should include the following.
FBC to rule out infection or anaemia.
Chemistry panel to rule out metabolic disturbances, hepatic encephalopathy.
Urinalysis to rule out infection.
Chest x-ray to rule out pneumonia, congestive heart failure, or other potential causes of hypoxia.
Drug levels in patients on digoxin, lithium, and quinidine, and alcohol if a history of alcohol abuse is suspected.
ECG to rule out myocardial infarction. A coronary angiogram may also be performed.
Arterial blood gas to evaluate for hypoxia, hypercapnia, and/or lactate (the latter commonly found in sepsis).
If no aetiology is identified from preliminary testing, further diagnostics should be considered including:
Lumbar puncture to rule out meningitis and encephalitis
EEG to rule out seizure activity and encephalopathy.[81]
Further investigations that may be done depending on the suspected cause include: sputum and blood culture, abdominal ultrasound scan, D-dimer, thyroid function tests, ACTH stimulation test, Venereal Disease Research Laboratory (VDRL) test, and fluorescent treponemal antibody test-absorption (FTA-abs).
How to perform a diagnostic lumbar puncture in adults. Includes a discussion of patient positioning, choice of needle, and measurement of opening and closing pressure.
How to take a venous blood sample from the antecubital fossa using a vacuum needle.
How to record an ECG. Demonstrates placement of chest and limb electrodes.
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