Elsevier

Sleep Medicine Reviews

Volume 12, Issue 5, October 2008, Pages 391-403
Sleep Medicine Reviews

Clinical review
Sleep in the intensive care unit

https://doi.org/10.1016/j.smrv.2007.11.004Get rights and content

Summary

Intensive care unit (ICU) environment is not propitious for restoring sleep. Alterations in sleep have potential detrimental consequences explaining increasing interest in the field over the last years. Methods to study sleep in ICU meets some limitations. Accurate sleep analysis requires full polysomnography, but polysomnographic patterns of normal sleep are frequently lacking in these patients and conventional scoring rules may be inadequate. Patients experience severe alterations of sleep with sleep loss, sleep fragmentation and sleep–wake cycle disorganization. Many factors may contribute to these abnormalities, including patient-related factors (e.g., disease severity) environmental factors (e.g., continuous exposure to light and noise, around-the-clock care, and medications). Health support techniques such as mechanical ventilation and sedation may also contribute to sleep disruption. The impact of sleep disturbances on morbidity and mortality in ICU patients remains unknown but inferences from experimental studies or indirect evidence suggest possible immune function alterations and neuropsychological dysfunction that could hamper weaning from assisted ventilation. Whether sleep disruption in ICU patients is independently associated with adverse outcomes or merely constitutes a marker for cerebral dysfunction remains to be determined. However, whatever signification and mechanisms of these alterations, now specific measures are recommended to protect sleep and circadian rhythm in ICU.

Introduction

That critical illnesses and environmental factors in intensive care units (ICUs) are associated with sleep disturbances was recognized shortly after the first ICUs were created. Many studies conducted over the last three decades have documented these sleep disturbances.*1, 2 Although polysomnography (PSG) remains the gold standard, analyzing sleep in ICU patients is a strenuous challenge and has important constraints, such as technical difficulties and conventional scoring.3 Sleep disturbances of critical care patients concern both sleep quantity and quality. Factors that fragment sleep are numerous and various, but do not explain the wholeness of arousals. Part of sleep alterations can also be due to conditions specific to ICU, such as mechanical ventilation and sedation. Despite considerable pieces of evidence for deleterious consequences of sleep alterations and sleep loss in experimental studies or in ambulatory patients, no direct pieces of evidence of such relation between sleep disruptions and morbidity have been published in ICU patients. There are possible resources to improve sleep in the ICU environment, however, prompting the pursuit of investigations.

Section snippets

Methods for sleep study in ICU patients

Sleep can be assessed in terms of quantity (total sleep time and time spent in each sleep stage), quality (fragmentation, sleep stage changes, wake after sleep onset, EEG sleep patterns), and distribution over the 24-h cycle. Full PSG remains the gold standard for sleep scoring but practical considerations have generated interest in alternative methods.

Subjective sleep quality

Sleep disruption is one of the most frequent complaints from ICU patients. In one study, disrupted sleep was the second most stressful factor reported by ICU patients.28 Among patients interviewed 3 days after ICU discharge, 61% reported sleep deprivation and 7% rated insomnia as their worst experience in the ICU.29 Sleep disturbances not only exist during the ICU stay but one follow-up study showed persistent sleep disturbances in up to 44% of patients 3 months after discharge.30

Sleep architecture

As mentioned

Factors responsible for sleep disruption in the ICU

Numerous factors contribute to sleep disruption in ICU (see Table 1). Some of them are not specific to ICU, such as noise, light, etc., although they are more intense and frequent in ICU. Some other conditions suspected to alter sleep are more specifically met in ICU, such as mechanical ventilation and sedation.

Adverse consequences of sleep disruption

Although several 24-h PSG studies found near-normal amounts of sleep, the marked sleep fragmentation is consistent with functional sleep deprivation. The impact of sleep deprivation and arousals on clinical outcomes of ICU patients has not been systematically studied. Sleep deprivation experiments in healthy volunteers have shown a number of effects, which are outlined below.

Sleep protection strategies in the ICU

Data suggesting detrimental effects of sleep disruption in ICU patients have prompted several investigators to evaluate sleep-preservation strategies.114 However recent data showed that minimizing light, noise, and nursing interventions failed to dramatically improve sleep.10 The use of earplugs improved subjective sleep properties in a group of critically ill patients and significantly increased the quantity and shortened the latency of REM sleep, although the number of awakenings remained

Conclusion

ICU patients experience severe sleep alterations with reductions in several sleep stages, marked sleep fragmentation, circadian rhythm disorganization, and daytime sleepiness. The numerous sources of these sleep alterations include endogenous factors such as disease severity and exogenous factors such as environmental conditions, medications, and sedation. The impact of these acute sleep alterations on the health of ICU patients remains unknown. Possible effects include immune function

Acknowledgement

B.C. was supported by grants from the Instituto de Salud Carlos III (expedient CM04/00096, Ministerio de Sanidad) and the Instituto de Recerca Hospital de la Santa Creu i Sant Pau.

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