To sleep or not to sleep: new insights in sleep-wake cycles and circadian rhythmicity in the intensive care unit

The main goal of this dissertation was to gain more insight into the sleep-wake behavior of intensive care unit patients and the factors that disturb it. At the beginning of this project, we firmly believed that patients experienced abnormal sleep-wake behavior. This was based on clinical observations and several (subjective) publications. Sleep is an essential physiological need, but can be difficult to achieve in the high-tech environment of the modern intensive care unit (ICU). Sleep deprivation has been associated with altered respiratory-function, immune-function, neuro-endocrine control, and could be the leading cause of a phenomenon called the "ICU-syndrome". It is generally believed that the ICU environment is responsible for these sleep disruptions, with noise being considered the most disruptive of all environmental stimuli. Unfortunately, these assumptions are based on evaluations of only small populations (n=12 in largest study) of selective groups of post-operative and cardiac ICU patients. The goal of this paper is to review current literature regarding sleep in the ICU, the influence of the ICU environment on sleep and the consequences of disturbed sleep in ICU patients.