Sleep during and following critical illness: A narrative review

Table 4 Summary of objective methods of sleep measurement in the critically ill

Method	Benefits	Limitations
Full polysomnography (PSG)	Gold standard technique; Provides polygraphic data on EEG, eye movements and chin tone; Established guidelines for interpreting data for normal sleep	Complex set up; Relatively expensive; Poorly tolerated in 25% of patients; Interferes with nursing care; May interfere with patient sleep; Interpretation requires sleep specialist; No validated criteria for atypical EEG found commonly in critically ill
Bispectral index (BIS) monitor	Small anatomic footprint; Simplified set up compared to PSG; Does not require sleep specialist for interpretation; Less affected by atypical EEG common in critically ill	Inaccurate differentiation of REM from N1/N2 sleep; Correlates weakly with RCSQ; No validated criteria for interpretation of results; Primarily designed to monitor depth of sedation
Limited lead EEG	Small anatomic footprint; Simplified set up compared to PSG; May not require sleep specialist for interpretation	Accuracy dependent on device and auto-staging software; Interpretation dependent on sleep specialist if not using auto-staging
Actigraphy	Minimally invasive; Simple set up; Easy to perform serial measures; Established use in outpatient setting	Poor accuracy compared to PSG and nurse observation, including over-estimation of total sleep time and sleep efficiency; Confounded by immobility, weakness, sedation, and neurological injury
Under mattress sensor	Non-invasive modality; Simple set up	Moderate agreement, but poor specificity compared to PSG; No correlation with RCSQ

EEG: Electroencephalogram; N1: Non-REM sleep stage 1; N2: Non-REM sleep stage 2; PSG: Polysomnography; REM: Rapid eye movement sleep; RCSQ: Richards-Campbell Sleep Questionnaire.