Many intensive care physicians have heard the comment, “At least the patient is asleep.” Yet critically ill patients often experience fragmented sleep, circadian disruption, and loss of restorative slow-wave and rapid eye movement (REM) sleep despite appearing asleep or being sedated.1,2 Increasing evidence suggests that sleep is a key component of recovery, with sleep disruption linked to delirium, delayed recovery, and long-term neurocognitive impairment.1,3
Understanding the unique nature of sleep disturbances in critical illness, the distinction between sedation and physiological sleep, and strategies to promote restorative sleep may provide an opportunity to improve both short- and long-term patient outcomes.
Why sleep matters
Sleep is a highly organized process involving cycles of nonrapid eye movement (NREM) and REM sleep. Slow-wave sleep, the deepest stage of NREM sleep, supports memory consolidation, immune regulation, and tissue repair.4 It also enhances glymphatic clearance of metabolic waste products, including β-amyloid and tau proteins, which may help preserve cognitive function.4,5 Sleep is also essential for maintaining circadian rhythms through interactions among the suprachiasmatic nucleus, melatonin secretion, light exposure, and homeostatic sleep drive. Critical illness disrupts these pathways, causing circadian dysregulation and abnormal sleep-wake patterns.3,6
While sleep deprivation in healthy individuals usually causes transient fatigue and impaired concentration, its effects in patients who are critically ill may be more serious. Combined with inflammation, organ dysfunction, medications, and physiological stress, sleep disruption has been linked to delirium, immune dysfunction, metabolic disturbances, delayed recovery, and long-term neurocognitive impairment.1,3
Sedation is not sleep
One of the most common misconceptions in critical care is that a sedated patient is a sleeping patient. From the bedside perspective, the distinction can seem academic. A patient receiving propofol, benzodiazepines, or opioid infusions may appear asleep and unresponsive. However, electrophysiological studies demonstrate that sedative-induced unconsciousness differs substantially from natural sleep. Natural sleep follows an organized architecture characterized by predictable cycling through NREM and REM stages. These stages are accompanied by coordinated neurochemical changes that regulate normal sleep architecture. Many commonly used ICU sedatives disrupt these normal physiological processes rather than reproducing them.6,7
Benzodiazepines suppress slow-wave sleep and REM sleep. Opioids fragment sleep architecture and reduce REM sleep.6,7 Propofol induces unconsciousness but does not reliably reproduce the restorative physiological characteristics of natural sleep.6,7 Consequently, a patient may spend hours appearing asleep while obtaining little of the biological benefits associated with restorative sleep. In short, unconsciousness is not synonymous with sleep.
Why sleep becomes disrupted in the ICU
Sleep disruption in the ICU is nearly universal and arises from a combination of environmental, physiological, and treatment-related factors. Noise from alarms, equipment, staff activity, and routine patient care frequently interrupts sleep, while nighttime light exposure and inadequate daytime light disrupt normal circadian rhythms.
Critical illness further impairs sleep through pain, dyspnea, anxiety, fever, inflammation, delirium, and organ dysfunction. Mechanical ventilation may contribute through patient-ventilator dyssynchrony, endotracheal tube discomfort, and recurrent respiratory-related arousals. Sedative medications, although often necessary, can also alter normal sleep architecture.3
As a result, patients who are critically ill commonly experience fragmented sleep, loss of circadian rhythmicity, and marked reductions in slow-wave and REM sleep.2 Polysomnographic studies show that sleep is often redistributed across the entire 24-hour period, with patients spending most of their sleep time in lighter stages and experiencing substantial reductions—or even absence—of the restorative sleep stages most important for recovery.2
Why should we care?
Short-term consequences
Sleep deprivation affects nearly every organ system. Cognitively, sleep loss impairs attention, executive function, memory formation, and emotional regulation. These effects may contribute to the development and persistence of ICU delirium, one of the most common complications of critical illness. Delirium is associated with prolonged hospitalization, increased mortality, higher health care costs, and worse long-term cognitive outcomes.3 Emerging evidence also suggests that disrupted sleep may contribute to the persistent cognitive impairment experienced by many survivors of critical illness.
Beyond its neurological effects, sleep deprivation has important consequences for immune, metabolic, cardiovascular, and respiratory function. Experimental studies have demonstrated alterations in both innate and adaptive immune responses, potentially impairing recovery from infection and systemic inflammation. Metabolic consequences include insulin resistance, impaired glucose regulation, and hormonal dysregulation, while cardiovascular effects include increased sympathetic activity, elevated catecholamine concentrations, and impaired autonomic control.3,6 In patients who are mechanically ventilated, fragmented sleep may also contribute to respiratory muscle fatigue and difficulty weaning from ventilatory support.1,3 Collectively, these observations highlight the broad physiological consequences of sleep disruption and reinforce the importance of sleep as a component of recovery from critical illness.
Long-term consequences
The consequences of sleep disruption often extend well beyond ICU discharge. Many survivors of critical illnesses report chronic insomnia, fragmented sleep, excessive daytime sleepiness, anxiety, depression, and symptoms consistent with posttraumatic stress disorder months to years after hospitalization.1 These symptoms are increasingly recognized as important components of post-intensive care syndrome (PICS)—a constellation of physical, cognitive, and psychological impairments that persist following critical illness.
Particularly concerning is the association between sleep disruption and long-term cognitive impairment. Between 30% and 50% of patients who leave the ICU experience persistent deficits in memory, attention, and executive function that may last for years after recovery from critical illness.1 Although multiple mechanisms likely contribute, including systemic inflammation, hypoxia, microvascular injury, delirium, and sedative exposure, sleep disruption may represent an important and potentially modifiable factor. Emerging evidence suggests that impaired slow-wave sleep may disrupt glymphatic function, reducing the clearance of neurotoxic proteins such as β-amyloid and tau.4,8 While direct causal relationships remain to be established, these findings provide a biologically plausible framework linking sleep disruption during critical illness to persistent neurocognitive dysfunction.
What can we do about it?
Importantly, sleep disruption may be at least partially modifiable.
Nonpharmacologic interventions
The strongest evidence for improving sleep in the ICU supports multicomponent nonpharmacologic interventions.3,6 Preserving normal circadian cues is a logical first step. During daytime hours, patients should be exposed to natural light whenever possible, encouraged to remain awake, and mobilized early. At night, lights should be dimmed, and unnecessary stimulation should be minimized to promote a more normal sleep-wake cycle.3,6 Noise reduction is equally important. Alarm optimization, staff education, designated quiet hours, earplugs, and environmental modifications have all been associated with improvements in subjective sleep quality.1,6
Care clustering may be one of the simplest and most effective interventions available. Consolidating medication administration, laboratory testing, and routine nursing assessments can substantially reduce unnecessary nighttime awakenings.3,6 Sleep promotion also requires attention to common clinical contributors to sleep disruption. Pain control should be optimized, recognizing that untreated pain remains a major cause of sleep fragmentation. Similarly, anxiety, dyspnea, and patient-ventilator dyssynchrony should be identified and addressed promptly.3 Although evidence supporting individual interventions varies, bundled approaches appear to provide the greatest overall benefit.3
Pharmacologic approaches
Pharmacologic strategies for sleep promotion in the ICU remain considerably less well-supported than nonpharmacologic interventions. Melatonin is an attractive option because it targets circadian regulation rather than simply inducing sedation. Although clinical trials have yielded mixed results, melatonin is relatively safe, inexpensive, and biologically plausible as an adjunctive therapy for sleep promotion in critically ill patients.3,6
Dexmedetomidine has generated particular interest because of its ability to produce electroencephalographic patterns that more closely resemble physiological NREM sleep. Several studies have demonstrated improvements in sleep architecture and reductions in delirium compared with benzodiazepine-based sedation strategies. However, dexmedetomidine should not be viewed as a dedicated sleep medication and should be used within the context of individualized sedation goals.3,6,7 In contrast, traditional hypnotic agents such as benzodiazepines, antihistamines, and antipsychotics lack strong evidence for routine sleep promotion in patients who are critically ill and may worsen delirium or further disrupt normal sleep architecture.3,6
The bottom line
Sleep disruption is one of the most common yet underrecognized complications of critical illness. Although many questions remain unanswered, the available evidence increasingly supports treating sleep as an essential component of ICU care rather than a secondary comfort measure. Strategies aimed at preserving circadian rhythms, minimizing nighttime disruptions, reducing unnecessary sedation, and promoting restorative sleep have the potential to improve both short- and long-term outcomes. As our understanding of ICU sleep continues to evolve, improving sleep quality may become an increasingly important therapeutic target. Perhaps the next frontier in critical care is not simply helping patients survive but helping them sleep well enough to recover.
This article was originally published in the Fall 2026 issue of CHEST Physician.
References
1. Altman MT, Knauert MP, Pisani MA. Sleep disturbance after hospitalization and critical illness: a systematic review. Ann Am Thorac Soc. 2017;14(9):1457-1468. doi:10.1513/AnnalsATS.201702-148SR
2. Elliott R, McKinley S, Cistulli P, Fien M. Characterisation of sleep in intensive care using 24-hour polysomnography: an observational study. Crit Care. 2013;17(2):R46. doi:10.1186/cc12565
3. Devlin JW, Skrobik Y, Gelinas C, et al. Clinical practice guidelines for the prevention and management of pain, agitation/sedation, delirium, immobility, and sleep disruption in adult patients in the ICU. Crit Care Med. 2018;46(9):e825-e873. doi:10.1097/CCM.0000000000003299
4. Xie L, Kang H, Xu Q, et al. Sleep drives metabolite clearance from the adult brain. Science. 2013;342(6156):373-377. doi:10.1126/science.1241224
5. Iliff JJ, Wang M, Liao Y, et al. A paravascular pathway facilitates CSF flow through the brain parenchyma and the clearance of interstitial solutes, including amyloid beta. Sci Transl Med. 2012;4(147):147ra111. doi:10.1126/scitranslmed.3003748
6. Lewis K, Balas MC, Stollings JL, et al. Executive summary of a focused update to the clinical practice guidelines for the prevention and management of pain, anxiety, agitation/sedation, delirium, immobility, and sleep disruption in adult patients in the ICU. Crit Care Med. 2025;53(3):e701-e710. doi:10.1097/CCM.0000000000006573
7. Benveniste H, Heerdt PM, Fontes M, Rothman DL, Volkow ND. Glymphatic system function in relation to anesthesia and sleep states. Anesth Analg. 2019;128(4):747-758. doi:10.1213/ANE.0000000000004069
8. Fultz NE, Bonmassar G, Setsompop K, et al. Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science. 2019;366(6465):628-631. doi:10.1126/science.aax5440
