Circadian rhythm disruption in severe sepsis: the effect of ambient light on urinary 6-sulfatoxymelatonin secretion

Purpose Properly regulated circadian rhythm supports physical and immunologic function. This rhythm is disrupted in patients with critical illness. We assessed the association between ambient light and circadian melatonin release, measured by urinary 6-sulfatoxymelatonin (6-SMT), in medical intensive care unit (MICU) patients with severe sepsis. Methods After excluding patients for renal failure or hepatic failure, blindness, and intracranial disease, seven patients were studied. No environmental manipulation was performed. Urinary 6-SMT specimens were obtained every 4 h. Light was measured in 1-min epochs for two sequential 24-h periods and compared to 6-SMT levels. Results No significant differences among urinary 6-SMT levels were found across 4-h time periods or between the 2 days (range 1,190.26 ± 1,040.81–4,738.57 ± 5,543.08 ng, 4-h period p = 0.09, 24-h day p = 0.50). Light levels were low and differed among 4-h periods, but not 24-h averages (minimum 2.32 ± 3.65 lux/min 00:01–04:00, maximum 70.11 ± 79.12 lux/min from 12:01–16:00, 4 h period p =