Circadian and Sleep Development in Preterm Infants Occurs Independently From the Influences of Environmental Lighting

Abstract

This study investigated the effect of intermediate nursery illumination on circadian rhythm and sleep development of preterm infants. Preterm infants were randomly assigned to one of two intermediate nursery rooms: a dimly lighted room, the dim (control) group, or a day-night lighted room, the cycled (intervention) group. Continuous rectal temperature and sleep were recorded at 36 wk postconceptional age (before discharge) and at 1 and 3 mo corrected age at home. Preterm infants are exposed to continuous low or unpredictable high illumination for several weeks or months in the neonatal intensive care unit (NICU) and intermediate care nursery. These infants are deprived of several potentially important maternal entrainment factors (1-4). This lack of maternal input and exposure to random/unpredictable lighting in the nursery may hinder the development of sleep and circadian rhythms and may adversely influence clinical outcome (5). It is hypothesized that regular lighting in the nursery will improve circadian rhythm development and thereby enhance clinical outcome. Indeed, earlier studies have shown beneficial clinical effects of cycled light in the nursery (6 -8). However, the shortor long-term influences of light on development of circadian rhythm were not examined in these studies. A prospective randomized study was initiated to address the hypothesis that cycled light before discharge may improve circadian organization and sleep compared with continuous dim lighting. METHODSPreterm infants who were admitted to our nursery at Lucile Packard Children's Hospital at Stanford were eligible. Exclusion criteria were short stay (Ͻ10 d) and transfer to another hospital, major congenital malformations, intrauterine growth retardation, grade 3 or 4 intraventricular hemorrhage, parenchymal injury including periventricular leukomalacia, prenatal infection, or substance abuse. When the clinical condition of an infant in the NICU was stable, he or she was transferred to the intermediate nursery and was randomly assigned to one of two groups: a dimly lighted room, the dim (control) group, or a day-night lighted room, the cycled (intervention) group. We assigned one room of our two-room intermediate care nursery to a continuous dim condition (dim room) in which the lighting remained low (below 20 lux) around the clock. The infant's incubator/bassinet was also covered by a nearly opaque blanket except during feeding or other interventions by parents and caregivers. This is the recommendation of the Neonatal Individualized Developmental Care Program (9), and during the time of this study, dim lighting 24 h/d was used as the standard practice at Stanford for all preterm infants. Infants in the cycled room also had their incubator/bassinet covered with the same type of blanket from 1900 h to 0700 h; however, the blanket was removed from 0700 h to 1900 h, at which time the room lighting was also turned up to standard lighting levels (approximately 300 lux) to produce a regular light-dark cycled condi-

The Effects of Creating an Artificial Night on the Pattern of Weight Gain Among Preterm Neonates

“…Besides, Boo et al (2002) conducted their study on neonates, who received mechanical ventilation, while our sample included no mechanically ventilated neonates. According to Mirmiran et al (2003), hospitalized neonates experience great stress induced by stressors such as constant and chronic exposure to poor or strong lighting, maternal separation, deprivation from maternal cuddle and deep sleep, and reactivity to light and sounds. Therefore, they conducted a study in 2003 in order to test the following hypothesis, "Neonates' sleep pattern and circadian rhythm are developed independently from environmental lighting".…”

“…Nonetheless, Boo et al (2002) found that premature neonates' exposure to cyclical twelve-hour lighting or continuous darkness did not significantly affect their weight gain (3). The results of studies by Kennedy et al (1997) and Mirmiran et al (2003) also illustrated that environmental lighting had no significant effect on neonates' weight gain (2,11).…”

“…Rivkees (2003) noted that preterm neonates' circadian rhythm is sensitive to light so that low-intensity light can regulate the development of their biological clock (8). Contrarily, Mirmiran et al (2003) stated that preterm neonates' circadian rhythm and sleep pattern are developed through the process of internal development and hence, environmental lighting has no significant effect on it (2).…”

“…Besides, advances in midwifery and neonatal intensive care have improved the survival of these neonates. Prematurity of preterm neonates' bodily organs leads to the need for prolonged hospitalizations (1,2).…”

The development of potentially better practices to support the neurodevelopment of infants in the NICU

“…424 Although there is a progressive shift towards sleep-wake circadian rhythmicity with maturation, this may occur independently of the amount of ambient light exposure, suggesting circadian entrainment may occur based upon an endogenous, exposure-independent pacer mechanism. 423,424 Presently, it is clear that the newborn does not achieve an obvious circadian pattern until 3 to 4 months chronologic age, and that, prior to term birth, there is an in utero entrainment.…”