PER3 Clock Gene Polymorphism, Clock Gene Expression and Delirium in the Intensive Care Unit. A Prospective Cohort Study.

An increasing number of patients are treated at ICUs worldwide. The majority of these patients survive critical illness and are discharged from hospital. In recent decades, improved therapy and survival at ICUs has increased focus on long term outcomes and post-ICU rehabilitation. Both physical and mental problems following admission for ICU therapy can be found for years after discharge. It is therefore important to discover factors that may have a significant impact for a worsened outcome, in order to prevent and treat these impairments.

Cognitive deficiencies may affect large proportions of the post intensive care population and mild cognitive impairment was demonstrated for up to 40% of the patients when evaluated three months after discharge. Recovery was slow and at one year follow up, 25% of the patients still showed impairment comparable to mild traumatic brain injury.

The presence of delirium during ICU stay has been associated with a worsened cognitive outcome at both 3 and 12 months follow up. Both patient's global cognition and especially executive function was impaired. Furthermore, a longer duration of the delirium period was associated with a poorer cognitive function. Incidence of delirium has also shown association to higher mortality rates and a longer hospital stay when compared to patients without delirium. In previous studies, the second day of admission has had the highest incidence of delirium.

Alterations in sleep architecture with a more shallow sleep and disruptions of the sleep wake cycle, is common in both ICU patients and patients with delirium. Sleep deprivation is often seen in delirious patients, and consequently, it has been suggested to be a risk factor for development of delirium.

The circadian rhythm is an inborn cycle of biological activity based on 24 hour intervals, and the rhythmicity interacts with sleep homeostasis in order to regulate sleep-wake cycles of individuals. In humans, the circadian rhythm is controlled by the suprachiasmatic nucleus (SCN) (the circadian clock) mediating melatonin secretion from the pineal gland to regulate the sleep-wake cycle. A number of factors, especially daylight, influence the SCN.