1. Introduction and Clinical Imperative

Delirium is an acute, fluctuating disturbance of attention and cognition that represents a form of organ dysfunction of the brain. It affects up to 80% of mechanically ventilated patients in the intensive care unit (ICU) and is independently associated with increased mortality, prolonged mechanical ventilation, extended hospital stays, and significant long-term cognitive impairment resembling dementia.

Despite its prevalence and severe consequences, delirium is frequently missed. Unstructured bedside assessments fail to detect up to 60% of cases, particularly the non-agitated, hypoactive subtype. The pathogenesis is complex, involving neurotransmitter imbalances (e.g., acetylcholine, dopamine), systemic inflammation crossing the blood-brain barrier, and profound disruption of the normal sleep-wake cycle. Therefore, integrating validated screening tools and a structured diagnostic work-up into daily ICU workflow is not merely best practice—it is a critical patient safety imperative.

2. Confusion Assessment Method for the ICU (CAM-ICU)

The CAM-ICU is a rapid, validated, and widely used bedside tool for delirium screening in critically ill adults. It has demonstrated excellent performance, with a sensitivity of 93–100% and a specificity of 89–100% in diverse ICU populations. The assessment is designed to be performed by nurses or other trained clinicians in under two minutes.

2.1 Diagnostic Criteria and Administration

The CAM-ICU evaluates four key features. A patient is considered CAM-ICU positive (i.e., delirious) if they exhibit Feature 1 AND Feature 2, plus EITHER Feature 3 OR Feature 4.

2.2 Common Pitfalls and Training

Accurate use of the CAM-ICU requires structured training and consistent application. Common pitfalls include attempting to assess deeply sedated or comatose patients (RASS –4 or –5, who are “unable to be assessed”), language barriers interfering with the inattention task, and inconsistent delivery of the standardized questions. To ensure high fidelity, institutions should implement formal training with didactics, video examples, and supervised practice, followed by annual competency checks. High inter-rater reliability (κ ≥ 0.8) is achievable with this approach.

3. Intensive Care Delirium Screening Checklist (ICDSC)

The ICDSC is an alternative validated tool that uses an 8-item checklist based on observations over an entire nursing shift. It provides an ordinal score from 0 to 8, with a score of 4 or greater indicating the presence of delirium. While the CAM-ICU provides a binary (yes/no) result, the ICDSC can also be used to track the severity of delirium over time.

3.1 Scoring Items and Thresholds

Each of the following eight items is scored as 1 point if present during the shift:

• Altered level of consciousness
• Inattention
• Disorientation
• Hallucinations, delusions, or psychosis
• Psychomotor agitation or retardation
• Inappropriate speech or mood
• Sleep-wake cycle disturbance
• Symptom fluctuation

A total score of 4 or more is diagnostic for delirium. A score of 1-3 suggests subsyndromal delirium.

3.2 Validation and Integration

The ICDSC has a reported sensitivity of approximately 74% and a specificity of 82% in mixed ICU populations. While its diagnostic accuracy is slightly lower than the CAM-ICU, its strength lies in its ability to quantify delirium severity. Worsening scores can trigger specific interventions, and improving scores can demonstrate response to therapy. The ICDSC should be completed at least every 12 hours and can be easily integrated into routine nursing assessments, with EHR calculators and alerts to flag high-scoring patients.

4. Additional Tools and Emerging Scales

While the CAM-ICU and ICDSC are the most robustly validated tools for the ICU setting, several other instruments exist. These are primarily used in non-ICU settings or are still under investigation for widespread ICU use.

• 3D-CAM: A 3-minute, structured adaptation of the CAM algorithm, well-validated for emergency department and hospital ward settings but less studied in ventilated patients.
• 4AT: A rapid (<2 minute) tool that combines alertness, orientation, attention, and acute change assessment. It is highly effective in older, non-ICU patients, but its validity in critically ill populations remains to be established.
• Cornell Scale for Depression in Dementia: This is a specialized tool for assessing mood in patients with pre-existing cognitive deficits and is not designed for acute delirium diagnosis.

5. Laboratory and Imaging Assessment

Once delirium is identified, a targeted work-up is essential to uncover and reverse contributing factors. This should be a systematic but judicious process, avoiding a “shotgun” approach.

5.1 Foundational Metabolic and Infectious Work-Up

The initial investigation should focus on common, reversible causes:

• Metabolic Panel: Check for electrolyte abnormalities (sodium, calcium, magnesium), renal failure (BUN, creatinine), and glucose dysregulation.
• Liver Function: Assess for hepatic encephalopathy with LFTs and an ammonia level if suspected.
• Infection Markers: A CBC with differential, CRP, or procalcitonin can signal infection. Obtain blood, urine, and other relevant cultures as clinically indicated.
• Oxygenation: An arterial blood gas can reveal hypoxemia or hypercarbia.
• Medication Review: Conduct a thorough review of all medications, especially sedatives (benzodiazepines), analgesics (opioids), and anticholinergic agents, which are common culprits. A toxicology screen may be warranted.

5.2 Escalated Neurologic Evaluation

Advanced neuroimaging and EEG are not routine for all delirium cases. They should be reserved for patients with specific “red flag” findings:

• CT or MRI of the Head: Indicated for new focal neurologic deficits (e.g., unilateral weakness), recent head trauma, or delirium that persists for days despite correction of all metabolic and infectious causes.
• Electroencephalogram (EEG): Indicated for suspected nonconvulsive seizures, particularly in patients with profound and unexplained altered mental status. In non-seizure encephalopathy, EEG typically shows generalized slowing or triphasic waves.

6. Subtype Differentiation and Clinical Implications

Delirium is not a monolithic entity. It presents with distinct motoric subtypes—hyperactive, hypoactive, and mixed—each with different clinical features, prognoses, and management priorities.

Management Implications

Recognizing the subtype guides initial management. Hyperactive delirium requires immediate focus on patient safety, including environmental modifications and, if necessary, judicious use of pharmacotherapy per sedation guidelines. In contrast, hypoactive delirium management centers on reviewing and reducing sedative medications, promoting early mobility and physical therapy, optimizing the sleep-wake cycle, and engaging family for reorientation.

7. Diagnostic Pathway Algorithm

A standardized pathway ensures consistent screening, evaluation, and management. It facilitates clear communication and timely, multidisciplinary interventions.