Delirium is a very common but annoying clinical state that interferes with the treatment
of background disease and delays recovery. Delirium is a troublesome condition that exhausts not
only the patient but also his/her family and healthcare professionals. Since aging is a risk factor for
delirium, how to control delirium is an extremely important issue in an aging society. Phenotype of
delirium is so diverse that it is difficult to elucidate the mechanism of individual symptoms, but it
is clinically well known that maintaining sleep quality is important in preventing and improving
delirium. Drugs and factors that are known to disrupt the sleep-wake cycle also overlap with the
risk factors for delirium, indicating the close connection between delirium and sleep. Although the
sleep-wake cycle is tightly regulated by many neurotransmitters and hormones, the role of each substance
in this cycle is being elucidated in detail. It is well known that acetylcholine is one of the
most important neurotransmitters involved in wakefulness, and anticholinergic drugs reduce rapid
eye movement sleep. Anticholinergic drugs are also the major drug causing drug-induced delirium.
Several clinical studies have reported that melatonin receptor agonists reduce delirium. Some clinical
studies have examined the relationship between delirium and environmental factors that interfere
with sleep, such as noise and brightness. The purpose of this review is to organize the cause of
poor sleep underlying delirium and propose strategies to prevent delirium, based on rich neurological
and pharmacological findings of sleep. We consider that elimination of causes of sleep deprivation
underlying delirium is one of the most effective prevention strategies for delirium.
Keywords: Acetylcholine, adenosine, delirium, histamine, melatonin, poor sleep.
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