Clinical Chronobiology: A Timely Consideration in Critical Care Medicine

Helen McKenna; Gijsbertus T. J. van der Horst; Irwin Reiss; Daniel Martin


Crit Care. 2018;22(124) 

In This Article


Critical care medicine aims to maintain homeostasis in patients undergoing extreme physiological stress, for which they are no longer able to compensate. To this end, we strive to maintain physiological measures within parameters that we hope will promote optimal cell function and lead to survival; refining our targets as new evidence emerges. However, one fundamental facet of life has failed to form part of our concept of a patient's well-being: the innate rhythmicity of their biological functions. We are all instinctively aware of the diurnal nature of our own behaviour throughout a 24-h period. We recognise the physical and mental affliction associated with its disturbance (e.g. jet lag and night shift work), but we give little consideration to the impact of these rhythms on the patients we treat. Most biological mechanisms fluctuate according to a circadian rhythm. The conservation of circadian rhythms across species points towards the survival advantage they convey, including: preparing an organism for daily recurring, and thus predictable, demands, such as the cyclical environmental changes in light, temperature and food availability imposed by the day–night cycle; and temporally segregating conflicting processes, such as feeding and physical activity, or sleeping and waking. The study of these cyclical phenomena, known as chronobiology, is growing in prominence throughout diverse disciplines, as their pervasive nature becomes apparent. During the extreme stress of critical illness, patients are particularly vulnerable from further impairment of cell function resulting from circadian rhythm disturbance. Critical care traditionally focuses on the "normalisation" of physiological indices, despite a limited evidence base,[1,2] but preservation of circadian physiology is not part of clinical practice. It is possible that neglecting the influence of circadian rhythmicity could contribute to the apparent lack of benefit from the majority of critical care targets tested in randomised controlled trials. In this review we introduce the basics of clinical chronobiology and propose the potential value to be gained from clinicians applying these new concepts to their daily practice. We propose that promotion of healthy circadian rhythms may constitute a future target for critical care medicine.