title: Circadian rhythm disruption in severe sepsis: the effect of ambient light on urinary 6-sulfatoxymelatonin secretion.
abstract: OBJECTIVE
  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 = <0.001, 24 h period p = 0.53). There was no relationship between light levels and 6-SMT excretion.
  
  
  CONCLUSIONS
  Circadian rhythm was disrupted in patients with severe sepsis, as reflected by disordered diurnal variation of urinary 6-SMT excretion. Light levels were low, exhibited limited diurnal variation, and did not entrain circadian rhythms in these patients.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Maryland School of Medicine, 110 S. Paca St, Second Floor, Baltimore, MD 21201, USA. Avercele@medicine.umaryland.edu
authors.forename: Avelino C
authors.initials: AC
authors.lastname: Verceles
authors.forename: Leann
authors.initials: L
authors.lastname: Silhan
authors.forename: Michael
authors.initials: M
authors.lastname: Terrin
authors.forename: Giora
authors.initials: G
authors.lastname: Netzer
authors.forename: Carl
authors.initials: C
authors.lastname: Shanholtz
authors.forename: Steven M
authors.initials: SM
authors.lastname: Scharf
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D021081:Chronobiology Disorders / Q000503:physiopathology*; D002940:Circadian Rhythm / Q000502:physiology*; D016638:Critical Illness; D005260:Female; D006801:Humans; D007362:Intensive Care Units; D008027:Light; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives* / Q000652:urine; D008875:Middle Aged; D010865:Pilot Projects; D011446:Prospective Studies; D018805:Sepsis / Q000150:complications*; D012720:Severity of Illness Index; D055815:Young Adult
chemical_list: C054513:6-sulfatoxymelatonin; D008550:Melatonin