T
he immature organ systems, including the brain,
of a preterm infant nursed in the neonatal intensive care unit (NICU)
are vulnerable to any change in the NICU milieu [1]. Mother-infant
contact is essential for the development of infants’ physiological
systems such as handling and regulation of stress, autonomic functioning
and sleep patterns [2,3]. However, prolonged stay in the NICU does not
allow a preterm infant the full benefit of mother-infant interaction.
In the past, it was assumed that newborns were not
sensitive to the environment, and hence not capable of interaction [4].
However, it is now evident that neonates, in addition to differentiating
between various stimuli and showing preference for certain stimuli, are
also capable of responding to touch. Unusual sensory experiences due to
frequent procedures, noise, excessive light in the NICU and prolonged
mechanical ventilation pose a risk to the developing brain of the
preterm infant, and adversely affect long-term neurodevelopmental
outcomes [5]. Thus, the physical environment of the NICU is very
important for the continued normal development of preterm infants. The
NICU environmental factors influencing long-term developmental outcomes
are outlined in Fig. 1.
|
Fig.1 Environmental factors in
neonatal intensive care influencing long-term developmental
outcomes.
|
Human neurosensory development is believed to follow
a particular sequence [6]. The first sensory system to develop is touch,
followed by kinesthetic, chemosensory, auditory and lastly the visual
system [7]. An atypically timed or an extremely intense stimulation of
one sensory system may not only affect the normal development of that
system, but may also affect other systems [8].
Noise
Differentiation of hair cells begins at 10-12 weeks
of gestational age (GA). At 25-29 weeks GA, the auditory system starts
to function and tonotopic columns are formed, which are essential for
development of complex language and musical skills [9].
BOX 1
Stages in Auditory Development |
Genetic Endowment (15-20 weeks GA): Basic structures
are formed based on genetic coding.
Endogenous Stimulation (20-22 weeks GA):
Regular nerve cell activity in the spiral ganglion forms
synchronous waves which help in axonal growth and formation of
synapses with relay nuclei.
Activity-dependent Processes (28-29
weeks GA to early months of life): Hair cells and their
cochlear connections start tuning for specific sound
frequencies.
GA: gestational age.
|
Stages in auditory development [6] that can be
blocked by exposure to low frequency noise (70-80 dB) and epigenetic
factors are shown in Box 1. As outer hair cells, which
receive feedback from brainstem and modulate sounds are functional only
closer to term, it is difficult for the preterm infants to modulate an
intense signal such as sound applied directly to the abdomen over the
uterus [10]. Thus, a loud sound (
³60
dB) in utero or in NICU at 25-26 weeks gestation can cause
changes in the autonomic functioning of the fetus that affects the heart
rate, oxygenation, gastrointestinal motility, blood pressure and sleep
[11]. As sick infants lack the reserve and the ability to self-regulate,
they are at increased risk for hypoxia and bradycardia. Recommendations
for sound levels in the NICU are shown in Table I [12].
The average decibel level of sounds in the NICU varies between 50 dB to
140 dB for various activities and interactions [13].
TABLE I Recommended NICU Standards for Sound Levels*
NICU sections |
Continuous background sound and |
Transient sounds or Lmax should
|
|
operational sound should not exceed |
not exceed |
Infant rooms and adult sleep areas
|
hourly Leq of 45 dB and an hourly L10 of 50 dB |
65 dB
|
Staff work areas, family areas and staff lounge areas |
hourly Leq of 50 dB and an hourly L10 of 55 dB |
70 dB
|
*Adopted from reference 12; Leq is the equivalent (average)
noise level across a given time-period; L10: A measure of the
decibel level that can be exceeded for only 10% of the time
(during a specific measurement period); Lmax: The highest
decibel level measured for at least 1/20th of a second duration
during the specified time period. |
Maternal tissues protect the fetus from most high
frequency sounds and light. Maternal voice, being low frequency, is
heard well and distinguished from in ero background noise.
Knowing the mother’s voice probably helps in mother-infant attachment
process and eventual language acquisition. The fetus can hear and learn
simple music or sounds common to the environment as early as 30-32 weeks
of gestation [14]. Brain waves generated during rapid eye movement (REM)
sleep aid in the formation of long-term synapses in the auditory cortex.
These synapses facilitate the neonate’s ability to learn. Hence it is
essential that rapid eye movement (REM) sleep cycles are protected [15].
Fetal learning is also linked to development of fetal
autonomic nervous system. Infants as early as 34-35 weeks gestation can
differentiate different emotional qualities of speech, music and moods,
which are stored as auditory memories in the limbic system [14,15].
Noise measuring technology in NICU is now accessible.
Re-echoing spaces and excessive noise are the main sources of noise
production. Thus, attention to NICU design, including sound-proofing is
very important. A study by Philbin, et al. [16] found greater
reduction in noise production after physical space change as compared to
staff behavioral change. Studies have aimed to reduce noise exposure in
NICU by using earplugs and earmuffs [17,18].
Few recommendations to protect sleep cycles
and possibly reduce adverse effects on infant’s auditory development, as
described in the literature [8] are provided below:
• Pregnant women should avoid prolonged exposure
to low-frequency sound above 65 dB.
• Direct application of earphones or other
sound-producing devices to pregnant woman’s abdomen or infants’ ears
should be avoided, as it is difficult to predict the sound level at
the fetal cochlea.
• The human fetus should hear mother’s voice
during ordinary activities of daily living during the last 6-8 weeks
and music and meaningful environmental sounds during the last 10-12
weeks of gestation, in utero or in the NICU. Live interaction
with parent voices at the bedside should be facilitated.
• NICUs should have regular noise assessment and
a program of noise control, including curtailment of talking and
laughing and gentle manipulation of incubator portholes.
• Monitoring equipment should be minimal, less
noisy or with visual alarms, and should not be placed on incubators.
Manufacturers should aim to minimize the noise levels in their
products.
• ‘Quiet period’ should be applied whenever
possible, especially during the night.
LiLighting
Visual development begins early in fetal life, and is
structurally and functionally complete around age 3 years, based on
neural plasticity. Stages involved in visual development are mentioned
in Box 2 [19]. Though excessive light in NICU was
previously considered to be a contributor to retinopathy of prematurity
(ROP) interventions for light reduction in NICU did not seem to prevent
it [20-22]. The dark environment of the fetus with its tactile,
kinesthetic and auditory stimuli along with mother’s pattern of rest and
activity [23] expose the fetus to circadian rhythms and probably
synchronize the fetal clock with the external light-dark cycle. The
circadian clock controls body temperature, alertness and rhythmic
hormonal production (e.g. melatonin, cortisol) [23]. Whether
acquiring circadian rhythms during gestation helps in timing the
physiological functions of the fetus to those of the mother is currently
unknown.
BOX 2
Stages in Visual Development
|
Activity-independent genetically controlled
and epigenetic processes: Basic structures and non-specific
connections are formed.
Activity-dependent processes:
• Endogenous spontaneous retinal wave stimulation
produced only during REM sleep directs and targets retinal ganglion
cell axons and organization of the visual cortex. Protecting sleep
cycles is important to avoid disrupting this organization.
• Visual stimulation begins with light and onset
of vision near 40 weeks.
• For continued visual development, regular visual experience
requiring light on objects, color and movement is essential.
|
Circadian rhythms have been documented as early as
zero to three days after birth [24]. Interrupted triggering of the fetal
circadian clock due to preterm birth or exposure of the preterm infant
to near darkness or continuous bright light in the NICU may negatively
impact NICU stay, sleep, feeding, growth and long-term neurodevelopment
outcome.
No benefit has been seen in preterm infants <28 weeks
gestation exposed to light-dark cycles. After 28 weeks, there is some
evidence in favor of cycled lighting [12]. Morag, >et al. [25], in
their review on the topic, concluded that many outcomes favored cycled
light compared with near darkness and continuous bright light.
Recommendations for lighting in NICU include:
• Repeated focusing on the mother’s (or human)
face and objects and activities within the focal distance seem to be
important.
• Provide some daily exposure to light (using
indirect light when possible), avoid sleep interruptions, bright and
direct lights, loud noises, high doses of sedative and depressing
drugs and unnecessary physical disturbing activities.
• Enhance dark periods by dimming light during
‘quiet period’ and protecting REM sleep.
• Be aware of the impact of overhead lighting as
well as light exposure from windows and rapid, abrupt changes in
lighting intensity.
• Shielding the incubator with a blanket or cover
to minimize light exposure is essential.
• Phototherapy lights increase light exposure to
infants in surrounding beds. Ophthalmic eye drops also cause light
sensitive eyes. Therefore, bright light should be avoided.
Parental Stress
Mother-infant bonding is a major problem in the NICU
[26] due to: maternal anxiety or depression, infant being ill, inability
to touch and hold the infant, loss of desired parenting role, isolation
and guilt about having a presumable unhealthy child, and unfamiliarity
of the NICU environment with bright lights, noisy monitoring machines,
ventilators, alarms and chemical odors. An important factor that
determines the effectiveness of parenting role after discharge is the
quality and frequency of parental involvement while in the NICU.
Parenting behavior is an important link between biological risk and
developmental outcome.
In a study by Turan, et al. [27], the stress
scores obtained by the Parental Stress Scale were significantly lower in
the intervention group (in which parents received information they
requested and all their questions were answered), in comparison to the
control group where parents were informed of only routine unit
procedures. Preyde and Ardal [28] showed that mothers in the
intervention group who were in a "buddy program" (individualized
telephonic support for a parent by a parent who had previous NICU
experience) and participated in educational group meetings had less
anxiety and depression, when compared to mothers in the control group
who received routine NICU services.
Family integrated care (FICare) is a new approach
that aims to promote weight gain among newborns admitted to the NICU at
21 days of life and lessen stress among parents. This novel method
involves the active participation of parents in the day-to-day care of
their newborn while in the NICU. FICare has four main pillars: parent
education, nursing staff education and support, psychosocial support and
NICU environment. Parents involved in FICare have less stress and
anxiety [29] with improved breastfeeding rates prior to discharge among
NICU patients [30].
Hence, the following strategies should be considered:
• Assurance, consistent information and a focal
person during NICU stay to answer questions.
• Parental participation in daily rounds and all
decision-making processes for their neonates.
• Emotional and spiritual support.
• Educational booklets and an album of nursery
graduates to provide hope and understanding of the NICU working
environment.
• NICU tours provided by other parents and
implementation of a buddy program.
• Encourage parents to provide daily routines
(feed, hold, bath, etc.) in stable infants, which will help with
transition of care following discharge.
• Parents should be involved in major milestones
such as first gavage feed, first 100 days of age, first time out of
isolette, etc).
Contributors: RV, AKL: conceptualized, carried
out data collection, drafted and edited the manuscript; MK, HA, AKL:
reviewed, edited and approved the final version.
Funding: None; Competing interests: None
stated.
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