Most people fall asleep more readily and sleep more soundly in familiar surroundings, except those with psychophysiological insomnia. This is exemplified by the ‘first night’ effect in the sleep laboratory, which is characterized by increased sleep latency, reduced stages 3 and 4 NREM sleep and in many subjects an increase in heart rate and blood pressure due to raised sympathetic activity induced by the uncertainty and unfamiliarity of the surroundings.

There are, however, features that are specific to certain locations of sleep.

Intensive care units
Sleep is almost invariably disturbed in intensive care units. There is a reduction in total sleep time at night, and a lack of consolidation of sleep, with a reduction in stages 3 and 4 NREM and REM sleep. Naps are frequently taken during the day and the circadian rhythms are readily disturbed. The main causes of these changes are as follows.

Continual sensory stimulation
In most intensive care units there is little daylight, but there is considerable artificial illumination at night.

The environment is noisy, not just because of the communication between members of staff and patients, but also because of alarms and other mechanical and electrical sounds _[21]. Frequent observations and procedures have to be carried out on patients, which disturb their sleep, and the ambient temperature is usually high.

Medical conditions
Hunger, thirst, pain and other symptoms, including nausea and diarrhoea, frequently disturb sleep. In sepsis there is a reduction in REM sleep with little definition of individual sleep states, which may even resemble status dissociatus.

Treatment effects
Drugs prescribed as sedatives and analgesics often considerably modify the sleep pattern. Even treatments such as mechanical ventilation can affect sleep, for instance by reducing arterial P_co2, leading to central apnoeas, and if irregular ventilator triggering leads to arousals from sleep _[22]. There is also a reduction n stages 3 and 4 NREM and REM sleep in response to surgery.

Psychological aspects
Anxiety about the cause, course and effects of the illness is almost universal in critical care units. Separation from the patient’s family and friends may contribute to insomnia, and confusion may result from sedative drugs or the effects of the illness itself.

The sleep restriction that develops may lead to hallucinations and delirium, which, combined with the underlying illness and medication, may cause amnesia for the episode. The post-traumatic stress disorder, with nightmares and flashbacks of the events, may also arise.

References