Although sleep is a physical state in which a person becomes relatively physically inactive and unaware of the environment, the brain never ceases its activity. This recurrent state is characterized by reductions in interaction with and awareness of the environment, lowered motility and muscular activity, and partial or complete temporary suspension of voluntary consciousness and behavior.1

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When sleeping, humans alternate between rapid eye movement (REM) sleep and non-REM (NREM) sleep. Each stage has its own signature brain activity. The polysomnogram is the primary tool for assessing sleep in the lab for both clinical and research purposes. During a polysomnogram, electroencephalography (EEG) and other sensors are used to categorize sleep in discrete stages. An EEG measures the electrical activity of the brain's neurons. In addition to EEG, common sleep studies also measure eye movements with electrooculography; muscle tone with electromyography (EMG); and cardiac activity with an ECG. Respiratory effort and effectiveness are measured with respiratory inductance plethysmography, pulse oximetry, and devices that measure apnea duration from airflow alteration, such as oronasal thermistry.2

Stages of normal sleep

NREM sleep comprises the majority of the total sleep time in adults. NREM sleep is divided into three substages: stage N1, stage N2, and stage N3.

Stage N1

A transition between wakefulness and sleep characterized by mixed EEG frequency of 4-7 Hertz (theta) for at least 50% of the epoch (30-second segment) and relatively low voltage, accounting for 10% or less of a total night's sleep in young adults.3

Stage N2

This stage is characterized by transient sleep spindles; EEG activity of 12-14 Hz which lasts a minimum of 0.5 seconds; and K complexes, EEG waves lasting about 0.5 seconds with a well-delineated negative deflection immediately followed by a positive one, creating a tracing resembling the letter K.3 High spindle frequency is correlated with sleep maintenance and brain plasticity and negatively correlated with mental health.4,5

Stage N3

Due to the large delta waves produced on an EEG recording, Stage N3 is also sometimes referred to as deep or delta sleep. A delta wave has an amplitude of greater than 75 millivolts and lasts at least 0.5 seconds with a low frequency (.05-2 Hz).3 Additionally, deep sleep has been called "restorative sleep" because cellular repair is very active in this stage.5,6 Stage N3 accounts for 10% to 20% of the sleep period in young to middle-aged adults but declines with age.3

The largest portion of N3 occurs in the early part of the sleep period and is characterized by slumber from which it is difficult to be aroused.3 During N3, parasomnias, such as sleepwalking, night terrors, and bedwetting are most likely to occur.3

REM sleep (stage R)

REM sleep is also called stage R or "dream sleep" due to the vivid dreams that occur during this stage and is divided into phasic REM sleep and tonic REM sleep. Bursts of rapid eye movements occur during phasic REM sleep and low muscle tone with corresponding limited motor activity during tonic REM sleep.3 Suppression of muscle tone occurs during this stage.1 EEG demonstrates a low voltage, mixed EEG pattern. Sawtooth waves are a common finding during REM sleep; these 2-6 Hz wave patterns are sharply contoured and occur in brief bursts.3 Deprivation of REM sleep results in a lack of memory consolidation.7

End of cycle

Completing REM sleep ends a "sleep cycle," defined as the regular alteration between NREM and REM, with each cycle lasting approximately 90 minutes.1

Sleep requirements

The amount of daily sleep for average adults is 7.5 to 9 hours, while children need longer periods.1 The timing of the sleep period also naturally varies across the lifespan. In addition to changes in sleep timing, the time spent in different sleep stages also varies over the lifespan: older adults spend less time in stage N3 and REM but more in stage N2.8 This decrease in stage N3 has implications for healing in this population since N3 is critical for cellular repair.1

Recovery

Adding extra hours of sleep above and beyond the normal requirements is necessary to decrease sleep debt. Making up for lost sleep is most efficiently accomplished by going to bed earlier rather than sleeping later into the morning; unfortunately, this does not eliminate severe sleep debt for most individuals.9 Sleeping regular hours all week long can decrease sleep debt.

Select sleep disorders

REM sleep behavior disorder (RBD)

Idiopathic RBD, a sleep behavior disorder characterized by behaviors that can occur during a loss of REM sleep atonia and dream-enactment behaviors, has gained attention as a prodromal marker for neurodegenerative disorders, including Parkinson Disease and Lewy body dementia.3,10

Sleep paralysis

Sleep paralysis is the complete inability to move for 1 or 2 minutes when waking or falling asleep. Sleep paralysis is a feature of narcolepsy.11 Rarely do healthy individuals experience sleep paralysis unless they are severely sleep-deprived.11

Narcolepsy

In narcolepsy, a syndrome of daytime sleepiness with cataplexy, transient muscle weakness can occur with brief episodes of muscle paresis as the patient directly enters into REM from being awake.3,12 Cataplexy can be triggered by events stimulating the sympathetic nervous system, such as excitement or laughter.3,12 Hypnagogic hallucinations, which are defined as vivid, often frightening sensory experiences not generated by external stimuli, perceptions, or mental activity also occur during an uncoupling of sleep and wakefulness.3 In these situations, REM, with accompanying sleep paralysis and dreaming, occurs after awakening.13

Sleep-related breathing disorders

Sleep-related breathing disorders are characterized by abnormal respiration during sleep; they occur in both adults and children. There are four major groups of sleep-related breathing disorders: central sleep apnea syndromes (a lack of signals from the brain to initiate breathing), obstructive sleep apnea syndromes (breathing interrupted by soft tissue obstruction of the airway), sleep-related hypoventilation disorders (breathing that is too shallow or too slow to produce adequate oxygenation), and sleep-related hypoxemia disorder (decreased oxygenation without high enough levels of CO₂ to initiate adequate breathing).

Functions of sleep

The body performs biological housekeeping during sleep, such as tissue repair and removing waste from the brain.14-17 During non-REM sleep, blood supply increases to muscles, energy is restored, tissues grow and are repaired, and children release growth hormones. Therefore, sleep deprivation can impact growth.18,19

Inadequate sleep can result from a child's environment or amphetamine-based medications prescribed for attention-deficit hyperactivity disorder (ADHD).20 Paradoxically, children exhibiting signs and symptoms of sleep deprivation, such as an inability to concentrate, may be misdiagnosed with ADHD.21

Without adequate sleep, the body is at a disadvantage in completing repairs.14,17,22 This is particularly important in the hospital setting, where patients must adequately recuperate from illness or surgery. A hospital's noisy environment may keep patients awake, and hourly patient assessments will arouse them, diminishing their ability to heal.

Sleep is also important for emotional well-being. Persistent sleep deprivation can cause significant mood swings, erratic behavior, and hallucinations.23

Sleep insufficiency

Research has shown that decreased sleep is associated with increased morbidity and mortality.24

Chronic sleep loss is associated with immunodeficiency, as evidenced by increased susceptibility to viral infections, such as the common cold.25-27 Chronic sleep insufficiency is correlated with increased heart disease, hypertension, diabetes, dementia, and obesity.28-31

Without enough sleep, the ability to perform even simple tasks, such as substituting one symbol for another or recognizing letters, dramatically declines.32 Without adequate sleep, the brain's ability to consolidate information is diminished through decreased long-term potentiation of neuronal synaptic strength, which is associated with learning and memory.33,34 Being less alert, attentive, and unable to concentrate effectively has obvious implications for nurses providing patient care.35

Night and shift work

Working the night shift impacts sleep-related processes. For example, artificial light at night extends the body's perception of natural daylight and delays the secretion of melatonin that promotes sleep onset.22 Treatment with exogenous melatonin has positive effects on sleep quality in patients with primary sleep and metabolic disorders, and respiratory diseases. However, exogenous melatonin use is not without potential adverse reactions, including daytime sleepiness, headaches, and dizziness, agitation, and increased bedwetting in children. Exogenous melatonin may also interact with anticoagulation and antiepileptic drugs; the safety of long-term melatonin use has not been established with controlled studies.36-39

Night-shift workers have an increased risk of type 2 diabetes.40 Shift work, night work, and changing schedules all contribute to sleep disturbance in healthcare workers.41 Also, research has highlighted gastrointestinal problems related to rotating shifts, such as deregulation of appetite.42-44 Leptin, the hormone that regulates appetite, is negatively correlated with sleep.31 Increased food intake associated with sleep loss can lead to weight gain through changes in hormone secretion, increasing hunger.45,46 Furthermore, irregular meal times contribute to sleep disturbances, such as the ability to maintain sleep-wake schedules, and are particularly problematic when eating close to bedtime.47

Possible links between chronic sleep insufficiency and dementia have also been documented, but not all studies report consistent results.44,48

Fatigue has been shown to be significantly associated with night work, less than 11 hours between shifts, shifts greater than 10 hours, and sleep disturbance in night-shift workers.49 High levels of poor sleep quality have been found in nurses, with the worst quality exhibited by those of the evening chronotype (night owls versus larks).50 Nurses working rotating shifts may spend more time in bed than their day-working counterparts but exhibit poorer quality of sleep.51 Sleep deprivation that impairs both short- and long-term memory can negatively impact nurses' ability to provide high-quality care.52

Sleep hygiene

Multiple studies have shown that information about sleep hygiene promotes better sleep:53

* Regular bedtime and rise time: maintain a consistent bedtime and wake-up time, even on your days off. Keeping "anchor hours," or four hours of consistent and fixed slumber daily helps reduce the negative impact of changing schedules on fatigue.

* To make up sleep, go to bed earlier and do not sleep later into the morning.51

* Exercise in the morning or early afternoon, particularly 4-6 hours before bedtime.

* Avoid caffeine, nicotine, and alcohol. If used, do not consume them near sleep onset. For example, although alcohol may help you fall asleep, it depresses REM sleep until metabolized and can cause a REM rebound resulting in awakening with vivid dreams that disrupt sleep.54

* Do not do anything in your bedroom except sleeping and having sex.56,57 White noise, interpreted as a "hissing sound," and pink noise, with characteristic frequency variation, have been shown to improve sleep.58

* Avoid napping. If you have any issues sleeping, you will only compound sleep problems. If you have no problems sleeping at night, they are not off-limits but should be a full sleep cycle, which means in increments of 90 minutes. If you cannot sleep 90 minutes, never nap longer than 20 minutes. This will keep you from entering stage N3, deep sleep. If you nap long enough to enter deep sleep, but do not complete a full 90-minute sleep cycle, you will not feel refreshed.59,60

* If you use an alarm to awaken, be sure to calculate how many 90-minute cycles you can get in after adding the time it normally takes you to fall asleep. Once you calculate how many cycles you can sleep, set the alarm for the end of a cycle. Do not add in those extra few minutes you long for, you will feel worse, not better, by waking yourself during a cycle.58

* Keep your bedroom cool. Natural sleep onset occurs as body temperature decreases.51

Nursing implications

Simple interventions, such as reducing noise at night, could help patients sleep more productively. Scheduling patient checks on a 90-minute interval (if clinical status allows) instead of hourly or every 2 hours, as is a common practice, could also enhance patient sleep by allowing for full sleep cycles. Avoid unnecessary light during patient turning or routine checks to minimize sleep disturbance.51 Routine environmental cleaning could occur during regular daytime periods rather than nighttime.

Sleep deprivation is positively correlated with decreased vigilance and work performance and workplace deviance, such as incivility and cyberloafing, which is the engagement in non-work-related online activities during work time.61-63 In addition, circadian misalignment related to nightwork may be linked to aggression.63

Knowledge of sleep and its impact on performance and health is important for nurses and their patients. Nurses should teach patients about sleep and its importance in health and well-being.

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