The investigators will perform a prospective, cohort study of 100 older intensive care unit (ICU) patients, to investigate the association between sleep disruption and ICU delirium.

Delirium and sleep disruption are both common in the intensive care unit (ICU). Delirium is a state of acute confusion, experienced especially by older adults admitted to the hospital, with the potential to adversely impact patients' outcome. Of hospitalized patients, the highest rate of delirium occurs in elderly patients in the ICU. Development of ICU delirium is associated with longer ICU and hospital length of stay, significantly higher risk of functional decline, loss of independent living, and increased mortality. Previous studies have focused on describing the clinical manifestations, risk factors and outcomes of ICU delirium; yet, the contribution of sleep timing, as well as its quality and quantity, to the development of delirium, has not previously been rigorously investigated. Sleep disturbance, including changes in sleep patterns and architecture, and decreased quality of sleep are commonly observed in older subjects. In the ICU, environmental factors (such as noise levels and continuous ambient light) and health care practices (such as frequent performance of medical procedures and tests) further contribute to sleep disruption in the critically ill older patients. Additionally, many sedative and analgesic agents potently suppress slow wave sleep. In preliminary data acquired from ICU patients, the investigators have observed that fragmented sleep is prevalent due to frequent arousals and awakenings, and that sleep architecture is altered with an increase in light sleep, and a decrease in restorative slow wave sleep. Despite the common occurrence of both ICU delirium and sleep disruption, it is not known whether sleep disruption increases the risk of developing delirium in the critically ill older patients. In this exploratory study, the investigators propose to test the hypothesis that the severity and duration of sleep disruption is an independent predictor of the onset and duration of ICU delirium in a cohort of older ICU patients. The investigators will measure sleep disruption using continuous processed electroencephalography and measure ICU delirium using a well-validated and reliable standardized instrument. Results from this study will inform the contribution of sleep disruption in the development of ICU delirium in the older critically ill patients.

Inclusion Criteria:

• patients ≥ 45 years of age admitted to the ICU, and remain for at least 24 hours.

Exclusion Criteria:

• status post craniotomy,
• moribund state with planned withdrawal of life support,
• severe dementia,
• substantial hearing impairment or inability to understand English.

The study population will include elderly patients admitted to the intensive care unit at UCSF.