Table 1 Summary of methods used in critical care for sleep measurement

Polysomnography

Gold standard Inter-rater reliability in critical care kappa = 0.79–0.83 [11,20,26,29]

Monitors sleep quantity and quality

Sleep technician needed continually during monitoring and to score results

Significant setup time required

Rater subjectivity, especially when scoring stage-1 sleep

Potential for monitoring electrodes to adversely affect sleep in non-sedated patients

Few critical care studies over multiple days

Cost – expensive setup and maintenance

Prone to patient dislodgement

Prone to electrical interference

Critical illness (for example, delirium may affect EEG)

Not practical for routine clinical use

Bispectral index

All patients with BIS values of less than 80 were asleep [9]

Can be used by non-specialists Sensor easily applied

Continuous attendance of technician not required

Low cost once monitor purchased

Trend screen provides quick view of immediate sleep quantity

Prone to patient dislodgement

Prone to electrical interference

Some patients may find sensor intrusive

Electromyogram activity may raise BIS value

Need to download into personal computer for complete evaluation

Critical illness (for example, delirium may affect EEG)

Not practical for routine clinical use

Validation and algorithm development required

Actigraphy

Correlation 0.72 to 0.98 versus polysomnography for total sleep time [60]

Not validated versus polysomnography in critical care patients

Non-intrusive

Can be used by non-specialists

Low cost once device purchased

Allows continuous measurement over days to weeks

Some actigraphs have a facility to measure light exposure simultaneously

Robust – unlikely to be removed by patient

Neuromuscular weakness increases risk of overestimating sleep quantity

Nursing staff may remove and not replace watch during washing, and so on

Periods of inactivity such as watching television scored as sleep

Yes – but only for circadian rhythm monitoring

Patient assessment

1. Verran/Snyder-Halpern Sleep Scale

Convergent validity (r = 0.39) only when polysomnography awakenings of more than 4 minutes scored [21]

No significant difference in total sleep time results compared to actigraphy [36]

1–4. If capable, patient can compare baseline quality with that currently experienced Relatively quick to complete

1–4. Cannot be used in cognitively impaired patients Memory problems may limit accuracy

Patient perception of nocturnal sleep may be adversely affected by circadian rhythm abnormalities

1,2,4. Yes – but exclude patients with delirium/dementia and beware of obvious patient sleep-state misperception

Patient assessment

2. Hospital Anxiety and Depression Scale (sleep component)

Not validated versus polysomnography [41]

3. Sleep in the Intensive Care Unit Questionnaire

Not validated versus polysomnography [3]

4. Richards-Campbell Sleep Questionnaire

Reliability (Cronbach's alpha = 0.90)

Correlation = 0.58 with polysomnography sleep efficiency index in critical care patients [11]

Nurse assessment

1. Direct observation

Direct observation at 5-minute intervals

Observation significantly overestimated polysomnography total sleep time [19]

Direct observation at 15-minute intervals. Nurses assessment of sleep state compared to polysomnography correct 81.9% of the time [22].

2. Echols' Patient Sleep Behavioural Observation Tool

Direct observation at 5-minute intervals. Moderate convergent validity demonstrated with polysomnography awakenings.

Single trained observer [21]

No significant difference in total sleep time results compared to actigraphy [36]

3. Richards-Campbell Sleep Questionnaire

Reliability versus patients (Cronbach's alpha = 0.83–0.95) [44,75]

1,3. Relatively easy to incorporate into routine nursing care

2. Attempts to qualify wake, non-rapid eye movement, and rapid eye movement sleep

1–3. Overestimates total sleep time

Frequent assessment required

Risk of data loss due to other direct and indirect nurse activities

3. Relies on nursing staff being able to make an accurate report of the patient's total sleep quality

1. Yes – but even with frequent assessment likely to overestimate total sleep time. This may limit its practicality and a compromise between frequency and accuracy will be necessary.

2. No – extensive observation required of eyelid positioning, respiration, and eye and body motility and responses

3. Yes – potentially the most useful sleep assessment tool currently available for clinical use