Home CHEST Thought Leaders Leveraging Circadian Cues to Improve ICU Outcomes

Leveraging Circadian Cues to Improve ICU Outcomes

By: Melissa P. Knauert, MD, PhD

We admit critically ill patients to the ICU. Stick tubes and needles in their bodies. Restrain them. Disturb them constantly day and night. Deprive them of natural light. Feed them around the clock. Give them high doses of drugs that alter brain function …Then we ask, “What pill will fix this?”

In the face of such a summary, it seems evident that no pill can surmount our inability to support normal brain function, including sleep and cognition, during critical illness.1 Sleep deprivation and delirium are complications of critical illness that significantly impact outcomes.2,3 Acute sleep deprivation has furthermore been linked to impairments in immune, metabolic, and cardiovascular function.4-6 In fact, the solution for ICU sleep deprivation and delirium likely requires that we meticulously drive the human body toward, rather than away, from homeostasis.

One of the fundamental biologic systems underpinning homeostasis is the circadian system. Virtually all cells and organs have diurnal variation in gene expression and function. Within the circadian system, a central master clock receives timing cues from the environment and, in turn, synchronizes timing across body systems. This process is called entrainment. Because organ function varies according to time of day, disruption of circadian signaling creates misalignment between physiologic demand and physiologic function at the end-organ level. With the aforementioned facts in mind, it is clear that supporting circadian entrainment is a critical foundation for strategies that can improve ICU sleep, prevent or treat delirium, and ultimately improve ICU outcomes. Thus, we must take steps to normalize circadian entrainment cues such as day-night light patterns, sleep-wake timing, and eating schedule.

Day-night light patterns are the most important circadian entrainment signal,7 and abnormal light exposure in hospitalized patients is a significant source of circadian disruption. Studies reveal that ICU environments share a common pattern of dim overnight light levels punctuated with frequent brief bright light pulses and remarkably low daytime light levels that are insufficient to promote normal entrainment.8,9 Strictly limiting overnight light exposure and providing bright daytime light is fundamental to supporting normal entrainment.

ICU sleep is severely compromised in terms of quality and timing.10 Disruptions in sleep-wake timing alter circadian alignment, which in turn further disrupt sleep-wake timing; this forms a vicious downward cycle for patients. Provision of a sufficient overnight sleep opportunity via clustering care and controlling overnight sound and light levels along with restriction of daytime sleep would promote both sleep and circadian normalization. Though expert guidelines recommend sleep promotion, changes in ICU workflow can be extraordinarily complex and therefore difficult to accomplish.11

Finally, the practice of continuous enteral feeding over 24 hours conflicts with the circadian rhythm of the digestive system puts patients at risk for disrupted glucose metabolism and incorrectly signals both central and other peripheral circadian clocks.12 Feeding schedules that more closely mimic daytime meals and snacks (ie, daytime bolus feeding) will improve circadian entrainment and coordination between organ systems.

In summary, efforts to address sleep in the ICU must be informed by circadian biology principals. Sleep cannot be supported by overnight quiet periods alone; these are necessary but not sufficient. A broader view of the problem incorporates the provision of sleep opportunity, overnight light restriction, bright daytime light, and daytime bolus feedings.

Dr. Melissa KnauertDr. Melissa Knauert specializes in critical care, pulmonary disease, sleep, and internal medicine. She has research interests focused on acute sleep deprivation in the ICU, atypical ICU sleep, and ICU circadian disruption. She attends in the medical ICU and is the Associate Director of the Sleep Fellowship Program at Yale New Haven Health System.


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