1. Clinical Presentation and Diagnostic Criteria

Accurate evaluation of sleep disturbance severity and etiology in critically ill patients is foundational to targeted interventions. ICU sleep disturbances manifest as fragmented, nonrestorative sleep with downstream effects on cognition and mood. Differentiation from delirium is critical.

A. Sleep Architecture Alterations

• Predominance of light sleep (N1–N2), with significant loss of deep (N3) and REM sleep.
• Frequent arousals, reduced overall sleep efficiency, and profound circadian misalignment.

B. Patient‐Reported Symptoms and Clinical Signs

• Subjective Complaints: Feelings of nonrestorative sleep, delayed sleep onset, daytime fatigue, and mood lability.
• Neurocognitive Signs: Inattention, disorganized thinking, and a fluctuating level of consciousness, creating a significant overlap with ICU-delirium.
• Mood Changes: Anxiety, irritability, and transient depressive symptoms are common.

C. Key Precipitants and Risk Factors

The ICU environment itself is a major contributor. Key factors include:

• Environmental: Constant noise, ambient light, and frequent care-related interruptions.
• Iatrogenic: Pain, mechanical ventilation, and sedative infusions, which can paradoxically suppress deep and REM sleep.

D. Differentiating Sleep Disruption from Delirium

While both conditions present with altered consciousness and inattention, delirium has distinct criteria and requires dedicated screening. Sleep disturbance is characterized by fragmented sleep and circadian misalignment without primary cognitive disorganization. Delirium, assessed via tools like the CAM-ICU, requires an acute onset, fluctuating course, inattention, and either disorganized thinking or an altered level of consciousness. It is crucial to administer sleep and delirium screening tools concurrently and avoid attributing cognitive changes solely to one or the other.

2. Subjective Assessment Tools

Patient‐reported instruments are vital for capturing the perceived quality of sleep, though their feasibility can be limited in intubated or delirious patients.

A. Richards-Campbell Sleep Questionnaire (RCSQ)

The RCSQ is a five‐item visual analog scale (0–100 mm) where the patient rates their sleep depth, latency, number of awakenings, return to sleep, and overall quality. It is validated in both ventilated and nonventilated ICU patients and shows moderate correlation with polysomnography findings and delirium risk. It should be administered daily, requires minimal training, and is responsive to sleep‐promoting interventions.

B. Other Subjective Scales

Tools like the Insomnia Severity Index (ISI) and the Hospital Anxiety and Depression Scale (HADS) were designed for general medical populations and are not formally validated for the acute ICU setting. Their reliance on patient recall and self-report limits their utility in intubated or delirious patients. They are best reserved for use in step-down units or post-ICU settings when communication has improved.

3. Objective Monitoring Modalities

Objective modalities are used to define sleep stages and architecture, but they face significant practical and interpretative challenges in the busy and noisy ICU environment.

A. Polysomnography (PSG)

PSG is the undisputed gold standard for sleep assessment, combining electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), and cardiopulmonary channels. However, its use in the ICU is largely limited to research settings or complex clinical cases (e.g., ruling out severe obstructive sleep apnea) due to equipment complexity, frequent electrode displacement, signal artifact from ICU devices, and the need for expert interpretation.

B. Actigraphy and Bispectral Index (BIS)

• Actigraphy: This wrist-worn device infers sleep from periods of limb immobility. Its utility is severely confounded by patient paralysis, neuromuscular blockade, or physical restraints.
• Bispectral Index (BIS): This processed EEG monitor provides a surrogate for sedation depth. It is not designed to be stage-specific for sleep and is highly susceptible to electrical noise and muscle artifact.

4. Classification and Severity Scoring

Standardized metrics help stratify patient risk, guide the urgency of sleep-targeted interventions, and identify important comorbidities like Obstructive Sleep Apnea (OSA).

A. Obstructive Sleep Apnea (OSA) Severity

B. ICU Sleep Architecture Patterns (EEG-Based)

5. Integrated Assessment Framework

A practical approach requires synthesizing subjective reports (RCSQ), delirium screening (CAM-ICU), and, when available, objective data (EEG patterns) to stratify risk and determine the urgency of intervention.

A. Risk Stratification Framework

B. Conceptual Algorithm for Initial Management