Clinical reviewSleep in the intensive care unit
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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2021, Critical Care Nursing Clinics of North AmericaCitation Excerpt :The ICU environment obfuscates this zeitgeber (external cue to entrain biological rhythms) secondary to the prolonged exposure to artificial lighting. The luminance levels within the ICU are reported to range between 5 lux and 1400 lux, whereby low luminance levels (<500 lux) for 20 minutes can result in a suppression of melatonin levels.74,75 Research attempting to address the issues attributed to restricted exposure to natural light levels suggest that use of bright light therapy (>1500 lux) may have a beneficial effect in reducing the need for pharmacologic intervention,76–78 and incidences of delirium among postoperative patients.79,80
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