Even during critical illness, the biological clock continues to play an important role. Understanding and accurately measuring 24-hour rhythms in intensive care patients is therefore essential. A new review by BioClock researchers examines how circadian rhythms are measured in intensive care unit (ICU) patients, what these measurements reveal, and how future research in this field can be improved.
For this review, researchers Floor Hiemstra, Lot van Winden, Laura Kervezee, and colleagues analyzed 35 scientific publications comprising data from nearly 288,000 patients admitted to intensive care units (ICUs). Most studies focused on rhythms in body temperature, heart rate, and blood pressure. The findings indicate that daily rhythms remain detectable in many ICU patients, despite the highly disruptive conditions of the hospital environment.
Altered Rhythms
At the same time, many studies showed that these rhythms differ from those typically observed in healthy individuals. Circadian patterns were often weakened or shifted in time. These findings are consistent with earlier evidence suggesting that both critical illness and the ICU environment can severely disrupt the biological clock.
The review also found associations between characteristics of circadian rhythms and clinical outcomes, including mortality and length of ICU stay. However, the interpretation of these relationships remains unclear. Stronger or weaker rhythms do not appear to have a straightforward meaning in all cases. They may reflect not only the state of the biological clock itself but also the severity of the underlying illness.
Greater Standardization Needed
One of the review’s key conclusions is that studies vary considerably in how 24-hour rhythms are analyzed. As a result, findings are often difficult to compare across studies. According to the authors, greater standardization of analytical methods is needed to improve our understanding of the role of the biological clock in intensive care.
The review highlights the potential of routinely collected patient data for circadian research. Because vital signs are continuously monitored in the ICU, these data provide a unique opportunity to better understand biological rhythms in critically ill patients, monitor them over time, and ultimately tailor care more closely to patients’ natural day-night cycles.
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