Patient care in the Intensive Care Unit (ICU) inevitably takes place around the clock. As a result, the contrast between day and night, which is so pervasive and prominent outside the hospital, is virtually absent in the ICU. Moreover, organ support and supportive care are typically administered with little regard to the time of day.
Despite such care activities being critical for patients, these conditions provide weak and conflicting timing cues to the circadian clock, the endogenous biological timekeeper that serves to optimally synchronize 24-hour rhythms in behavior and physiology.
In critically ill patients, circadian disruption is common and often severe, manifesting as aberrant amplitudes and altered peak timing of daily rhythms in clinical, hormonal, and molecular parameters. Our short review published in Intensive Care Medicine discusses opportunities for circadian medicine in the ICU.
The disturbance of circadian rhythms in ICU patients may not only be a consequence of organ dysfunction but also a contributing factor to ongoing organ failure. Organ-specific clock genes are controlled by the suprachiasmatic nucleus (SCN) in the hypothalamus. The SCN does not just process environmental light cues from the retina and synaptic inputs from other brain areas but also receives feedback from the periphery by circulating hormones and autonomic signals.
Based on this intricate crosstalk between the circadian system and health outcomes, the emerging field of circadian medicine offers a wide range of opportunities to optimize intensive care medicine and improve health outcomes in critically ill patients. All with the ultimate objective of supporting the healing process of critically ill patients through the preservation and restoration of circadian homeostasis.