Relationship of Melatonin Levels in Blood and Urine with Sleep Quality in Children Admitted to Pediatric Intensive Care Unit

Abstract

Highlights: What are the main findings? Children admitted to the PICU frequently fail to achieve the recommended amount of sleep for their age. Altered serum and urinary melatonin levels are significantly associated with poorer sleep quality. What is the implication of the main findings? In the PICU, circadian rhythm is disrupted. Among modifiable factors that contribute to this, are the environmental factors such as artificial lighting, noise, and nocturnal interventions. Melatonin is a potential non-invasive biomarker of circadian dysfunction in the PICU setting. Objectives: Melatonin regulates the sleep–wake cycle, which may be altered in children admitted to the pediatric intensive care unit (PICU). The aim is to analyze whether blood and urine melatonin levels are related to sleep quality in children admitted to the PICU. Methods: A single-center, prospective observational study was conducted at the PICU in a tertiary referral center in Madrid, Spain. It included patients (1 month–16 years) admitted to the PICU. Results: A total of 40 children were included in the study (52.5% male), analyzing 2 days for each patient (80 total study days). The median age of the patients was 34.5 months. The median number of hours of sleep over the whole day was 9.9 h (IQR 8.4–12.6); nighttime was 7.5 h (IQR 6.5–9) and daytime was 2.5 h (IQR 1.4–5.7). Only 8.5% of patients slept the appropriate number of hours of nighttime sleep for their age. High serum melatonin levels in the morning were correlated with more nocturnal awakenings (r = 0.35, p = 0.01) and less continuous sleep time (r = −0.29, p = 0.03). Altered urine levels in the morning correlated with shorter 24 h total sleep time (r = −0.43, p = 0.01). Inadequate urine levels at 7 pm correlated with a shorter duration of continuous nocturnal sleep (r = −0.37, p = 0.03). Conclusions: Children admitted to the PICU often do not achieve the recommended hours of sleep for their age. A significant percentage of these children exhibit an altered melatonin secretion pattern, which is associated with shorter nighttime sleep duration and longer daytime sleep duration.