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Delirium screen and it's significance in critically ill patients

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Delirium screening in critically ill patients

Delirium is an acute, fluctuating disturbance of attention, awareness, and cognition caused by an underlying physiological insult, medication/substance effect, or multiple causes. It may be hyperactive, hypoactive, or mixed. In the ICU, the quiet or hypoactive form is common and easily missed.

Why screen?

Delirium is a form of acute brain dysfunction in critical illness. It is not simply “ICU psychosis” or an expected harmless consequence of being critically ill.
Routine screening is important because:
  • It is commonly missed clinically, particularly hypoactive delirium. One ICU text reports that delirium may be overlooked nearly 70% of the time without structured assessment.
    Fishman’s Pulmonary Diseases and Disorders, p. 2680.
  • It can be the first clue to a reversible problem, such as hypoxaemia, sepsis, shock, pain, urinary retention, constipation, hypoglycaemia, electrolyte disorder, renal/hepatic failure, alcohol or drug withdrawal, or medication toxicity.
  • It identifies potentially modifiable iatrogenic contributors, especially deep sedation, benzodiazepines, excessive opioids, immobility, sleep disruption, isolation, and lack of sensory aids.
  • Delirium is associated with worse outcomes, including longer mechanical ventilation, longer ICU and hospital stay, higher mortality, cognitive impairment at discharge and months later, functional decline, and greater need for institutional care. Persistent delirium not attributable to sedatives is particularly associated with poor outcomes.
    Harrison’s Principles of Internal Medicine, 22e, p. 2547.
  • A positive screen triggers a focused search for cause and delivery of preventive and supportive measures, not automatic antipsychotic prescribing.
Current ICU guidance supports screening adult ICU patients regularly, commonly once per nursing shift, using CAM-ICU or ICDSC, as described by the ICU delirium monitoring guidance.

Before any delirium test: assess arousal

Use a sedation-agitation scale, most commonly the Richmond Agitation-Sedation Scale (RASS).
  • If the patient is comatose or not arousable to voice, delirium cannot be assessed reliably.
  • For CAM-ICU, assessment generally proceeds only if the patient is arousable to voice, commonly RASS -3 or higher.
  • Record coma/deep sedation separately and reassess after sedation is lightened where clinically safe.
This distinction prevents calling sedation-related unresponsiveness “delirium.”
Fishman’s Pulmonary Diseases and Disorders, p. 2680.

Main ICU delirium screening tools

ToolMethodPositive resultKey strength
CAM-ICUBrief bedside test, usually 1-2 minutesFeatures 1 + 2, plus feature 3 or 4Fast, suitable for intubated/non-verbal patients
ICDSCEight-item checklist observed over 8-24 hoursUsually score ≥4/8Captures fluctuating symptoms across the entire shift
Both CAM-ICU and ICDSC are validated for critically ill adults, can be used by trained ICU nurses and clinicians, and are recommended screening instruments.
Fishman’s Pulmonary Diseases and Disorders, p. 2680.

1. CAM-ICU: Confusion Assessment Method for the ICU

It assesses four features:
  1. Acute onset or fluctuating course
    Is there an acute change from the patient’s baseline mental status, or does it vary during the day/shift?
  2. Inattention
    The patient cannot focus or sustain attention, often tested with letter recognition or simple visual commands.
  3. Altered level of consciousness
    Anything other than alert and calm.
  4. Disorganized thinking
    Incorrect answers to simple questions or inability to follow simple commands.
CAM-ICU positive = Feature 1 + Feature 2 + either Feature 3 or Feature 4.
It is particularly practical for ventilated patients because it does not require spoken responses.
Fishman’s Pulmonary Diseases and Disorders, p. 2680.

2. ICDSC: Intensive Care Delirium Screening Checklist

The ICDSC documents observations over a nursing shift or 8-24-hour period. It includes:
  1. Altered level of consciousness
  2. Inattention
  3. Disorientation
  4. Hallucinations, delusions, or psychosis
  5. Psychomotor agitation or retardation
  6. Inappropriate speech or mood
  7. Sleep-wake cycle disturbance
  8. Fluctuation of symptoms
A score of 4 or more suggests delirium. Scores below this may indicate subsyndromal delirium and warrant close observation and prevention measures.

Clinical significance of a positive delirium screen

A positive screen should lead to action:

1. Confirm and assess causes

Review for:
  • Oxygenation, ventilation, haemodynamics, fever, sepsis
  • Glucose, sodium, calcium, renal and liver function
  • Pain and untreated withdrawal
  • Medication list, especially benzodiazepines, anticholinergics, opioids, corticosteroids, and other psychoactive drugs
  • Urinary retention, constipation, dehydration
  • New neurological injury, seizures, or stroke when indicated
  • Hearing/visual impairment and absence of glasses or hearing aids

2. Reduce modifiable risks

Use non-drug measures first:
  • Treat pain appropriately
  • Target light sedation where safe
  • Avoid or minimise benzodiazepines unless specifically indicated, such as alcohol withdrawal
  • Daily spontaneous awakening and breathing trials when appropriate
  • Early mobilisation
  • Orient the patient repeatedly: clock, calendar, familiar voices, explanation of procedures
  • Promote sleep: reduce nighttime noise/light and cluster care
  • Ensure daytime light exposure
  • Restore hearing aids and glasses
  • Encourage family engagement when feasible

3. Communicate and trend

Document the score and compare it with prior shifts. Delirium fluctuates, so a single negative test does not rule it out. Escalate persistent or worsening delirium, especially when there is a new focal neurological deficit, severe agitation threatening safety, or concern for seizures or intracranial pathology.

Key nursing points

  • Screen at least once per shift and after meaningful changes in sedation, neurological status, or clinical condition.
  • Do not judge delirium only by agitation. A sleepy, withdrawn, inattentive patient may have hypoactive delirium.
  • Do not perform CAM-ICU/ICDSC in a comatose patient. Record sedation state and reassess later.
  • A positive tool is a screen, not a substitute for clinical assessment. Consider delirium a prompt to identify and correct causes.
  • Avoid treating the score alone with sedatives. Sedatives can worsen or mask delirium.

Bottom line

Delirium screening with CAM-ICU or ICDSC converts a frequently missed, fluctuating neurological complication into a detectable bedside problem. In critically ill patients, it helps uncover reversible pathology, guides sedation and supportive care, and identifies patients at increased risk of prolonged ventilation, longer ICU stay, death, and long-term cognitive impairment.
Recent systematic reviews continue to evaluate ICU delirium burden and tool performance. Relevant recent evidence includes PMIDs 41117943 and 38538305.
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