The Intensive Care Unit and Sleep

Ynhi Thai

Sachin Talathi

Paul G. Cox

Camilo R. Gomez

Paul R. Carney

James D. Geyer

INTRODUCTION

Sleep constitutes a third of the human life span and is an important homeostatic requirement for the human body (1). It is a restorative period that allows for growth, repair, hormone secretion, and protein synthesis and is usually an initial response in acute infections (1). Without adequate amounts of sleep, negative immune, cognitive, and behavioral effects could occur. In the intensive care unit (ICU), sophisticated technologies provide the monitoring and intervention strategies required, but treatment often comes at the expense of sleep. Routine care, noise, lighting, mechanical ventilation, and a number of other factors often deprive those of sleep who need it the most. Sleep deprivation and disruption of the circadian rhythm can counteract the healing process within the ICU. This chapter will explore causes of sleep disruption while in the critical care setting, circadian rhythm disruption, the general connection between sleep and immune parameters, potential consequences of sleep deprivation, ICU psychosis, and suggestions for improvement. In addition to problems specific to the ICU, the more common sleep disorders including obstructive sleep apnea and restless legs syndrome are common in the intensive care setting.

CAUSES OF SLEEP DISRUPTION IN THE ICU

Noise

Noise is measured on a logarithmic scale or in decibel units as dB. Some effects of excessive noise include hearing loss, anxiety, and cardiovascular stimulation (2). The US Environmental Protection Agency suggests that noise levels within hospitals should not exceed 45 dB during daytime and 35 dB during nighttime (3). Noise levels within the ICU can range between 50 and 85 dB, with peaks as high as 103 dB (2,4,5). Typically, any sound level >40 dB can interfere with sleep (3). A study within an ICU reported that at 60 cm away from a patient’s head, the noise level ranged from 60 to 80 dB with no significant decrease 180 cm away (5).

There are several sources of noise within the ICU, including conversations between staff members, visitors, fellow patients, ventilator alarms, cardiac monitors, telephones, television, and other routine activities. It is widely recognized that noise can affect the sleep-wake cycle. In a questionnaire given to patients in a neurosurgical ICU, 57.6% of those who had sleep problems reported that the cause was from being within a noisy environment (6). One report showed that environmental noise accounted for 17% of awakenings and 11.5% of arousals from sleep (7). In an interview of 100 patients 3 to 7 days after discharge from the ICU, patients identified the inability to lie comfortably, more so than noise, as the main cause of sleep disturbance (8). Patients’ ability to adapt and to increase their awakening threshold may account for the reason why environmental sound is not a major contributing factor to sleep disruption for some studies (2). Some individuals can increase their arousal threshold to >80 dB(A) (3). Nonetheless, the impact of noise on general health should not be ignored.

Medications

Common medications given to many ICU patients, especially those who are postoperative or intubated, can adversely affect sleep physiology. Benzodiazepines are commonly used to reduce anxiety and promote sleep (9). In healthy subjects, these hypnotic drugs increased stage 2 sleep, decreased
slow-wave sleep (SWS) and rapid eye movement (REM) sleep, and slightly increased total sleep time (TST) compared with baseline nights (10,11). Benzodiazepines can cause other side effects such as sleep deprivation, dependence, tolerance, and long-term memory impairment (12).

Opioids are used for pain management. Their receptors are within the same nuclei that regulate sleep (13), and they can minimize SWS and REM sleep (9). Morphine, a common member of the opioid family, can increase stage 1 sleep (14). Other side effects of opioids include dependency and tolerance.

Beta-blockers can decrease TST, SWS, and REM sleep, whereas tricyclic antidepressants can extend SWS and inhibit REM sleep (9). Catecholamines given for blood pressure support or to increase cardiac output can cause alertness and restlessness by inducing the cortical activating system (14,15). More research is required to determine the effects that these drugs have not only on sleep but also on the overall health of the critically ill patient.

Degree of Comfort

Recovery is often a long process for the critically ill who are covered with monitors, ordered bedrest, and burdened with discomfort. Immobility and the inability to lie comfortably is often one of the main factors inhibiting sleep (6,8). Monitoring equipment, alarms, thirst, tracheal suctioning, inability to talk, odd smells, and room temperature can add to the degree of discomfort (15,16). Pain is also a major contributor to sleep disruption (6,17). It has been shown that burn patients have poor sleep quality during the night due to pain and discomfort, with the average sleep time being about 6 hours with frequent arousals (18,19). Electroencephalography monitoring of nine patients who underwent general surgery revealed that TST was significantly reduced, with five of the individuals unable to sleep on the first postoperative day (20). Moreover, SWS accounted for <5% of TST, and REM sleep was partially or completely diminished in these patients.

Lighting

The normal functioning of the circadian rhythm appears to be disrupted within critically ill patients, in which sleep is redistributed over a 24-hour period (3). This could be induced by artificial light within the ICU. Some rooms do not have windows, eliminating natural lighting altogether, which could cause disorientation (21). Light intensities can exceed 1,000 lux in an ICU at night, whereas 100 lux is enough to alter melatonin secretion (9). However, it has been suggested by some that lighting does not significantly affect patients’ sleep in comparison to other factors (9,15).

Nursing Care

Routine nursing care can disrupt the sleep pattern of patients in the ICU. An observational study by Tamburri et al. (2004) found that most frequent interactions with patients occurred at 8 PM, midnight, and 6 AM. Only 9 out of the 147 nights observed had a 2- to 3-hour period without any disturbances. During the study, care interventions generally occurred every 1 to 2 hours, with nurses and staff assessing vital signs, administrating medications, turning patients, bathing, and other routine activities. In questionnaire responses by patients who were recently discharged from the ICU, vital sign measurements and blood sampling were considered to be more disruptive than noise, light, and medication administration (22). Furthermore, just the feeling of constant observation can make patients feel uneasy and contribute to sleep disturbance (6). Although nurses may be aware of the importance of sleep, physician orders and nursing policies result in an environment that promotes poor sleep (15).

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