The restorative effects of proper circadian rhythm and sleep-wake cycle are well known. Disruption of these processes in the MICU is likely multifactorial - a result of critical illness, coupled with unregulated light, noise, and social stimuli. The purpose of this study is to determine how typical, ambient light in our MICU can regulate circadian rhythms in patients with severe sepsis.
Patients in this cohort study were admitted to the MICU for severe sepsis/septic shock (SS). Patients were excluded if they had renal or hepatic failure, blindness, or an intracerebral process in close proximity to the pineal gland or thalamus. Demographic information was recorded and severity of illness was calculated using APACHE II scoring. Treatment for SS was conducted per Surviving Sepsis Guidelines. No environmental manipulation was performed. Urinary melatonin levels (ng/ml) were obtained every 4 hours, and total melatonin excretion was calculated using urine volume. Ambient light was measured (lux) in minute epochs, and was correlated to urinary melatonin levels. All data was collected over a 48 hour period.
Baseline characteristics were recorded (table 1). There was no significant change in urinary melatonin secretion across six hour periods, with a nadir noted during 0:01–6:00 (Range: 9108.7±7047.3ng to 2581.0±2030.2ng, p=0.065, ANOVA). Light levels were dismally low (figure 1), but significantly different when comparing day and night (maximum 88.3 lux/min from 6:01–18:00, minimum 9.1 lux/min 18:01–6:00, p=0.009, ANOVA).
Circadian rhythms are disrupted in patients with SS, as reflected by abnormal urinary melatonin secretion. Light, despite maintaining diurnal variation, is not present in intensity great enough to maintain circadian rhythms in these critically ill patients.
The poor regulation of light and other uncontrolled stimuli in the MICU may contribute to circadian rhythm and sleep-wake cycle disruption in the critically ill. Given the positive effects of proper circadian rhythms and sleep-wake regulation, greater benefit may be achieved by combining novel environmental regulation with accepted therapeutic strategies for treating patients with severe sepsis and other critical illness.
Avelino Verceles, No Financial Disclosure Information; No Product/Research Disclosure Information