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KEY POINTS

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  • Sleep is necessary for life, and disrupted sleep and circadian rhythmicity have been linked to a variety of adverse health outcomes. It is likely that critically ill patients are harmed by poor sleep, although evidence to support this contention does not yet exist.

  • Until further research is conducted, recommendations for improving sleep in critically ill patients are drawn upon limited evidence and extrapolations from other patient populations.

  • Critically ill patients exhibit disordered circadian timing, which may contribute to poor sleep and adverse health outcomes. These abnormalities may reflect an inability of critically ill patients to synchronize their internal clocks to the ICU environment, although it is likely that acute illness and medications also contribute to these abnormalities.

  • Exposure to bright light during the day (particularly the morning) and avoidance of nocturnal light exposure may strengthen circadian rhythmicity and promote sleep.

  • Patients receiving continuous intravenous sedation are likely at increased risk of disordered circadian rhythmicity due to low retinal light exposure from sedative-induced eye closure.

  • The typical ICU environment is hostile to sleep, consisting of excessive light and noise at night, insufficient light during the day, and frequent sleep disruption due to monitoring and patient care activities.

  • In general, the sleep of critically ill patients is highly fragmented and nonconsolidated, and rapid eye movement (REM) sleep is scarce.

  • Sleep and mechanical ventilation is a bidirectional interaction in which changes in the level or pattern of mechanical ventilatory support may affect sleep, while changes in sleep state affect respiration and therefore patient-ventilator interaction.

  • Patients receiving mechanical ventilation are susceptible to sleep disruption if air hunger is not sated, if neural and mechanical inspiratory times differ, if periodic breathing is induced, and probably through other mechanisms as well.

  • Sleep fragmentation from periodic breathing is most likely to occur when pressure support ventilation is used, particularly if the patient has also heart failure. Proportional assist ventilation may also induce periodic breathing and sleep fragmentation, but appears less likely to do so. Volume-cycled assist control ventilation may be the mode of ventilation that is least likely to disrupt sleep in critically ill patients.

  • Traditional sleep scoring criteria are unreliable in assessing sleep in mechanically ventilated patients receiving intravenous sedation.

  • Patients receiving continuous mechanical ventilation and continuous intravenous sedation exhibit pronounced temporal disorganization of the sleep EEG. The extent to which sedation is itself restorative is not clear.

  • Sleep may play an important role in the short- and long-term physical, cognitive, and psychological recovery of recent survivors of critical illness.

  • Absent high-quality evidence to guide the clinician, efforts to enhance sleep, and circadian rhythmicity in the ICU should focus initially on relatively low-hanging fruit: for instance, administering baths during the daytime or early evening hours, and ensuring adequate light exposure during the day.

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INTRODUCTION

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It is still not clear exactly why we sleep, although there are many theories. What is clear is that sleep is a ubiquitous and highly conserved ...

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