Abolished circadian rhythm of melatonin secretion in sedated and artificially ventilated intensive care patients

BACKGROUND: Sleep disturbance is common in intensive care patients. Aside from its unpleasantness, there is a correlation with intensive care unit (ICU) syndrome/delirium. Reasons for sleep deprivation appear to be multifactorial, including the underlying illness, an acute superimposed disturbance, medications, and the ICU environment itself. There are reasons to believe that alterations of the 'biological clock' might contribute. Melatonin secretion is one reflection of this internal sleep/wake mechanism. Melatonin levels are normally high during the night and low during daytime, being suppressed by bright light. METHODS: Melatonin levels in blood and urine were studied over 3 consecutive days in eight critically ill patients during deep sedation and mechanical ventilation. Sedation was assessed with the sedation-agitation (SAS) scale and bispectral index (BIS) monitor. RESULTS: The circadian rhythm of melatonin release was abolished in all but one patient, who recovered much more quickly than the others. There was no correlation between melatonin levels and levels of sedation. CONCLUSIONS: This study indicates that dyssynchronization of the melatonin secretion rhythm is common in critically ill and mechanically ventilated patients. It could be hypothesized that an impairment of the melatonin rhythm may play a role in the development of sleep disturbances and delirium in intensive care patients, and that melatonin supply could reduce the incidence of these phenomena.