Circadian Disruption in Critical Illness

Abstract

Circadian rhythms play a vital role in metabolic, hormonal, and immunologic function and are often disrupted in patients in the ICU. Circadian rhythms modulate the molecular machinery that responds to injury and illness which can impact recovery. Potential factors contributing to the alteration in circadian rhythmicity in intensive care unit (ICU) patients include abnormal lighting, noise, altered feeding schedules, extensive patient care interactions and medications. These alterations in circadian rhythms in ICU patients may affect outcomes and therefore, normalization of circadian rhythmicity in critically ill patients may be an important part of ICU care.

Keywords: ICU; circadian rhythm; critical illness; sleep; trauma.

Figure 1

Schematic representation of the circadian system. The suprachiasmatic nucleus (SCN), the central circadian clock, is entrained by light and other stimuli. The SCN coordinates the activity of peripheral clocks and is, in turn, affected by them. These circadian clocks regulate various physiologic processes.

Figure 2

Diurnal variations in melatonin, cortisol and temperature. Depicted here is the variation over 24 h. Time of day is denoted on the bottom. The light bars represent time subjects are normally awake and the dark bar represents a typical 8 h sleep time. Adapted from (20).

Figure 3

Schematic representation of the change in melatonin levels over 48 h. The time of day at which peak melatonin levels are reached is the phase. The amount of time between two phases is the period. A change in the phase indicates a time shift in the circadian clock. A change in the period to more or <24 h indicates that the circadian clock is no longer being entrained. Time of day is denoted on the bottom. The light bars represent time subjects are normally awake and the dark bars represents a typical 8 h sleep time.