Clinical review: Sleep measurement in critical care patients: research and clinical implications

Abstract

Sleep disturbances are common in critically ill patients and have been characterised by numerous studies using polysomnography. Issues regarding patient populations, monitoring duration and timing (nocturnal versus continuous), as well as practical problems encountered in critical care studies using polysomnography are considered with regard to future interventional studies on sleep. Polysomnography is the gold standard in objectively measuring the quality and quantity of sleep. However, it is difficult to undertake, particularly in patients recovering from critical illness in an acute-care area. Therefore, other objective (actigraphy and bispectral index) and subjective (nurse or patient assessment) methods have been used in other critical care studies. Each of these techniques has its own particular advantages and disadvantages. We use data from an interventional study to compare agreement between four of these alternative techniques in the measurement of nocturnal sleep quantity. Recommendations for further developments in sleep monitoring techniques for research and clinical application are made. Also, methodological problems in studies validating various sleep measurement techniques are explored.

Trial registration: Current Controlled Trials ISRCTN47578325.

Figure 1

Scatterplots of the results of four different techniques used to measure nocturnal sleep in our intervention studies: (a) bispectral index (BIS) quantity versus actigraphy, (b) BIS quantity versus patient assessment (Richards-Campbell Sleep Questionnaire), (c) BIS quantity versus nurse assessment, and (d) nurse assessment versus patient assessment.

Figure 2

Bland-Altman plots. Horizontal lines are drawn at the mean difference and at the mean difference plus and minus 1.96 times the standard deviation of the differences: (a) bispectral index (BIS) quantity versus actigraphy, (b) BIS quantity versus patient assessment (Richards-Campbell Sleep Questionnaire), (c) BIS quantity versus nurse assessment, and (d) nurse assessment versus patient assessment.