Introduction 

 Preterm birth, a major concern during the perinatal period, has a global annual incidence of around 13 million (1). The infant born prematurely is placed in an environment quite unlike that experienced at any other time of life (2). Neonatal intensive care unit (NICU) provides excess stimuli, therefore, preterm infants can become overstimulated if cared for in an NICU.

An important role of the neonatal nurse while providing care is to promote the preterm infant’s growth and development through the control of the NICU environment (3,4).(3), (4).

The fetus develops in an environment rich with auditory, tactile, and kinesthetic sensory stimuli, circadian rhythms provided by the mother, and Near darkness (ND).

The term infant continues to develop in a Cycled light (CL) environment with increasing circadian influences and multiple sensory stimuli. Thus, the needs of preterm infants can not be extrapolated from what is known to be best for fetuses or healthy term infants (5). One aim of modern neonatology is to create an environment to mimic that experienced in utero as closely as possible. However, the NICU environment is not optimal for preterm neonates, as it differs significantly from that experienced by the fetus, at least with respect to noise, light, temperature, and handling (2).

 The American Academy of Pediatrics and the American College of Obstetricians and Gynecologists recommend neonatal care under cycled lighting (CL) conditions (i.e., lights on during daytime and lights off at night) instead of care in a continuous 24-hour bright or irregular Dim lighting (DL) environment (6) .

Light has both positive and negative potential effects on health and development. Continuous bright light has been related to infant stress as manifested in increased activity levels, decreased sleep, and bradycardia. Yet, CL has the potential to promote circadian rhythms with health benefits including hormonal regulation, activity- rest cyclicity, and vital sign regulation (5).

The circadian rhythm influences the rhythmic production of several hormones (melatonin, cortisol, growth hormone), respiratory and cardiac function, sleep-wake state, the level of alertness and body temperature. The circadian clock in mammals is located in the suprachiasmatic nuclei in the anterior hypothalamus and is present by 18 weeks of gestation. This master circadian clock organizes and orchestrates the timing of all biological functions, from complicated physiological systems to single cells  (7).

Thus, growth might either be decreased with the stress related to exposure to bright light or increased with the development of circadian patterns and rest-activity rhythms when exposed to CL. Length of hospitalization is directly related to the infant’s ability to gain enough weight to reach discharge weight criteria; thus promotion of growth is a primary goal of neonatal care (5).

This study investigated the effect of creating an artificial night on physiological changes in preterm infants in the hope that even a small step to be taken in order to promote growth and health of preterm infants.

Materials and Methods

This was a RCT study on which 38 infants who had a medical condition for stability and in order to gain weight and become mature were hospitalized in the neonatal intensive care ward in Ghaem Hospital, Mashhad-Iran; were selected( April 2012 to October 2012) . 

First infants selected by non-probabilistic method and then divided into two groups by weight 1700-1200g and 2200-1701g and then randomly assigned to one of two groups divided the light period and continuous lighting. Each infant was assessed for 10 days.

Inclusion criteria included: 1200-2200 g birth weight, healthy infants without congenital anomalies, lack of pathologic apnea and feeding through a nasogastric tube or oral gastric and neonatal age range studied was 1-7 days.

Both study groups in demographic variables such as gestational age, age at entry into the study, birth weight and weight at entry into the study, amount of received calories, care time of kangaroo mother care, time Nothing Per Orem (NPO) before entering the study, feeding time, type of nutrition, use or non-use of optimal and Medium-chain triglycerides (MCT’s) oil, also the type of training that about the mother's breast milk was given to the mothers and kind of care they received, were homogeneous.

Demographic characteristics of the mother and infant, infant information before and after inclusion in the study, which was completed daily and during the study.  

Credit of collection tools data were evaluated using content validity, to assess reliability, the reliability equivalence was used.

Each study group of infants under continuous and period light illumination, after a minimum of 12 hours of birth and their stability, also feeding through a nasogastric or gastric oral, were care in incubator, in both groups during the study were received  similar care.

Infants in the light period, for 10 days, received light in the form of a sequence of day and night. The light from 7 hours to 19 with the usual light and dark period from 19 to 7 that the lamps were lit room and incubators were covered with cotton fabric.

Incubators coverage from 19 hours to 7 only when the infant feeding and nursing care was pushed. Infants were monitored throughout the night with pulse oximeter.

Feeding infants in both groups were performed every 2 hours, and most infants were breastfed and formula-fed. The study of the control group was 10 days, in this way, the babies all day long in normal light of ward were.

Vital signs in infants in the intervention group included abdominal breaths in one minute and saturation of arterial oxygen incubated in the supine position, before covering the incubator at 19 and again at 7 am was controlled.

Ambient lighting levels in infant spaces shall be adjustable through a range of at least 10 to no more than 600 lux (B1 to 60 foot candles), as measured on a horizontal plane at each bedside (8). Of course, the light intensity should be reduced during sleep. Using a lux meter with mark Tenma revealed that 17 lux of light to pass through the cotton fabric. For statistical investigation, descriptive statistics (frequency, percentage, and average ± normal deviation) were used.

For comparing quantitative findings between groups the statistical test of independent t-test was used. The study was done using SPSS16 statistical software.

Results

In this study, in the control group, 36.8% were female and 63.2% were male, and in the intervention group, 47.4% were female and 52.6% were males.

The mean gestational age of infants in study was 31.39±1.39 that was in the range of 30-34 weeks. Using an independent t-test revealed that the two groups are equal. Respiratory rate was lower in the intervention group than the control group 

(Table.1) and the results of the statistical analysis of repeated measures suggests that the difference between the two groups was significant (P<0.05).

Results showed that in both study groups, the level of oxygen saturation in the intervention group higher than the control group (Table. 2) and the results of the statistical analysis of repeated measures suggests that the difference between the two groups is significant (P<0.05).