RESEARC H Open Access
Effects of earplugs and eye masks on nocturnal
sleep, melatonin and cortisol in a simulated
intensive care unit environment
Rong-fang Hu
1
, Xiao-ying Jiang
1*
, Yi-ming Zeng
2
, Xiao-yang Chen
2
, You-hua Zhang
3
Abstract
Introduction: Environmental stimulus, especially noise and light, is thought to disrupt sleep in patients in the
intensive care unit (ICU). This stud y aimed to determine the physiological and psycho logical effects of ICU noise
and light, and of earpl ugs and eye masks, used in these conditions in healthy subjects.
Methods: Fourteen subjects underwent polysomnography under four conditions: adaptation, baseline, exposure to
recorded ICU noise and light (NL), and NL plus use of earplugs and eye masks (NLEE). Urine was analyzed for
melatonin and cortisol levels. Subjects rated their perceived sleep qu ality, anxiety levels and perception of
environmental stimuli.
Results: Subjects had poorer perceived sleep quality, more light sleep, longer rapid eye movement (REM) latency,
less REM sleep when exposed to simulated ICU noise and light (P < 0.05). Nocturnal melatonin (P = 0.007) and
cortisol secretion levels (P = 0.004) differed significantly by condition but anxiety levels did not (P = 0.06). Use of
earplugs and eye masks resulted in more REM time, shorter REM latency, less arousal ( P < 0.05) and elevated
melatonin levels (P = 0.002).
Conclusions: Earplugs and eye masks promote sleep and hormone balance in healthy subjects exposed to
simulated ICU noise and light, making their promotion in ICU patients reasonable.
Introduction
Sleep disruption is common in ICU patients and has
been characterized by several studies using polysomno-
graphy (PSG) [1-3]. Adverse consequences of sleep dis-
ruption include impaired immune function, decreased
inspiratory muscle endurance, negatively affec ted wean-
ing fr om mechanical ventil ation, and a possible associa-
tion with delirium and severe morbidity [4,5]. The
causes of sleep disruption in the ICU are multifactorial.
The ICU environment is thought to be an important
factor in sleep disruption [6].
Numerous studies have fo und excessive noise levels in
the ICU, often with nighttime peaks of more than 80 dB
(A) [5,7]. In a ddition, subjective and objective studies
both demonstrate that patients have been disturbed by
ICU noise [1,8-10]. Light ex posure is another important
sleep dis ruptor in ICU settings. Reported nocturnal illu-
mination in ICUs varies widely, with mean m aximum
levels of 5 to 1400 lux [5,11]. Light exposure is the pri-
mary external cue for circadian rhythm. In addition,
nocturnal melatonin secretion can be acutely suppressed
by light, and 100 lux is sufficient to impact nocturnal
melatonin secretion [12]. Throughout the past decade,
evidence has been accumulating for the altered secretion
of melatonin in ICU patients. ICU patients suffer from a
severe lack of sleep associated with loss of the nocturnal
melatonin secretion pattern [13,14]. Therefor e, effective
interventions to promote sleep in ICU patients are
urgently needed.
Despitemanyclaimsthattheuseofnoisereduction
and lighting practice in an intensive care environment
may improve the patient’s sleep quality, there have been
few objective studies to evaluate the effects of these
interventions [15-17]. Most research in this area has
focused purely on noise reduction and not explored the
combined effects of ICU noise and light factors on
* Correspondence: xiaoyj320@163.com
1
School of Nursing, Fujian Medical University, Jiaotong Road 88, Fuzhou,
350004, PR China
Hu et al. Critical Care 2010, 14:R66
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© 2010 Hu et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/li censes/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provid ed the original wor k i s properly cited.
physiological and psychological outcomes, including
sleep architecture, perceived sleep quality and hormone
secretion (melatonin and cortisol). No studies have yet
evaluated the effects of earplugs and eye masks on the
sleep of ICU patients as measured by PSG and hormone
secretion.
We hypothesized that patients’ sleep is disrupte d by
the noise and light in the ICU, accompanied by
impaired nocturnal melatonin secretion and elevated
cortisol secretion. Earplugs and eye masks worn during
exposure to a sim ulated ICU environment may improve
sleep and protect nocturnal melatonin and cortisol
secretion. To test this hypothesis, an experimental study
was conducted in a sleep laboratory.
Materials and methods
Research design
This study used a repe ated measures design. Four noc-
turnal nine-hour (10:00 p.m. to 7:00 a.m.) periods of
sleep were measured, including adaptation, baseline,
exposure to recorded ICU noise and light (NL), and NL
plus use of earplugs and eye masks (NLEE). All subjects
(n = 14) underwent a total of four overnight PSG.
To minimize order effects, earplugs and eye masks
were randomly worn on either the third ( n = 7) or
fourth (n = 7) night (Figure 1). For each subject, study
nights were spaced one day apart to avoid delay effects.
Subjects were asked to keep a sleep diary to record their
rest, activity and diet during the study period.
Subjects were asked to provide two nocturnal (10:00 p.m.
to 7:00 a.m.) urine samples, during base, NL and NLEE
nights. Urine levels of melatonin sulfate and cortisol were
determined by ELISA and radioimmunoassay (RIA),
respectively.
All s ubjects completed a sleep scale and the Chinese
version of the Spielberger State Anxiety I nventory (SAI)
[18] at 7:30 a.m. after every experimental night to record
perceived sleep quality and anxiety levels, respectively.
The study was performed at the Sleep-breath D isor-
ders Center at the Second Affiliated Hospital, Fujian,
China. The study design was approved by the research
ethics boards of the hospital and the Fujian Medical
University.
Subjects
Subjects were in cluded in the study if they were non-
smokers, older than 18 years of age, had no hearing pro-
blem as determined by a hearing screening t est , had no
sleep disorders, scores of 7 or less on the Pittsburgh
Sleep Quality Index (PSQI), had no history of night-shift
work i n the past three years and agreed t o abstain from
caffeine and alcohol for 12 h ours prior to each study
night. All provided written informed consent before
being enrolled in the study.
Figure 1 Study design.
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Subjects were excluded if PSG on the adaptation night
found any sleep disorder including s leep apnea, narco-
lepsy, chronic insomnia or restless leg syndrome. Female
subjects were excluded while they were menstruating.
Subjects were recruited by advertisements posted at
the Second Affiliated Hospital. Fourteen subjects were
enrolled in the study. Each was paid 200 Yuan Renminbi
at the end of the study.
Instruments
Recorded ICU noise
ICU noi se was cont inuously monitored for 24 hours
using a sound meter, model AWA5610D (AWAI, Hang-
zhou, China) i n five ICU environments: a surgical ICU
(SICU), a coronary care unit (CCU), a cardiac surgical
ICU (CSICU) and two medical ICUs (MICU). All had
noise levels far exceeding the 20 dB(A) at nighttime
recommended by the Guidelines of the Chinese Associa-
tion of Critical Care Medicine (2006)[19]. The SICU was
the loudest. The mean (standard deviation) noise value
in the SICU was 70.1 ± 11.9 dB(A), the peak noi se level
recorded was 95.3 dB(A), and the minimal noise value
was 51.4 dB(A) . Thereafter, ambient noise of the SICU
and CSICU were recorded digitally during a typical
weeknig ht shift and stored on computer for playback in
the sleep laboratory. The sound recording equipment,
modelICD-P320(SonyInc.,Tokyo,Japan)wasposi-
tioned at the bed of patients receiving mechanical venti-
lation. Simultaneous sound meter readings were taken
to ensure similar noise levels during playback in the
sleep laboratory.
Lighting conditions
Nighttime illum ination in fiv e ICU settings and the
sleep laborat ory were monitored by a light det ector,
model TES1332 (Taiwantes, Shenzen, China). In all set-
tings, light was provided by ceiling fluorescent lights.
The light detector was placed as close as possibl e to the
head of the bed of a patient receiving mechanical venti-
lation, but not so as to interfere with patient car e. L ight
measurements were taken every hour for 24 hours. Fi ve
ICUs maintained high mean night l ight levels ranging
between 50 and 238.6 lux, with highest mean nighttime
light levels in the SICU and CSICU. Mean nighttime
light levels in the sleep laboratory measured 100 lux
with the light on, and 5 lux with it off and the door to
the hallway shut. Therefore, the study used 100 lux to
simulate the ICU lighting condition.
Earplugs and eye masks
Subjects were instructed to wear earplugs with 29 d B
noise reduction rating (3 M Corporation, Beijing,
China) and eye masks during experimental night
NLEE. Subjects chose from three types of e ye masks
provided.
Polysomnography
Sleep was assessed by PSG using the Polysmith 2003
sleep acquisition and analysis system (Neurotronics, Gai-
nesville, FL, USA). The standard proc edure for sleep
measur ement described by Rechtschaffen and Kales [20]
was followed. Subjects were hooked up to record elec-
troencephalogram (EEG), eye movement and sub-mental
electromyogram (CHin EMG) in t he sleep lab oratory.
During NL and NLEE nights, recorde d ICU noise was
played and fluorescent lights turned on. A sound meter
wasplacedattheheadofthesubject’s bed and the
recording time synchronized with t he sound meter to
ensure playback in a similar range of decibels to that
recorded. Electrode impedances were w ithin acceptable
limits (<10kQΩ). PSG equipment was located outside
the subject’s room. Sleep variables (sleep period time,
sleep efficiency index, sleep onset latency, rapid eye
movement (REM) lat ency, arousa l index and percentage
of sleep in REM, stage one, two and three) were scored
manually by two scorers independently who were una-
ware of the experimental conditions, according to stan-
dardized criteria [20,21].
Melatonin and cortisol
Nocturnal urine was collected between 10 p.m. and
7 a.m. on baseline, NL and NLEE nights. The containers
were wrapped with black plastic t o protect the urine
from light. The amount was recorded and two samples
of each 2 ml were frozen to -20°C for later analysis.
Concentrations of 6-sulphatoxymelatonin (6-SMT), the
stable metabolite o f melatonin, were measured by
enzyme-linked immunometric assay (IBL, Hamburg,
Germany) in duplicate. Concentration of cortisol, a
stress-related hormone, was measured in another urine
sample b y RIA (Beijing North Instit ute of Biological
Technology, Beijing, China).
Subjective measurements
Subjective sleep quality was assessed by a visual analog
scale developed by the researchers based o n previous
scales [22]. Subjects evaluated their sleep quality on a
scale of 0 to 10 (0 = e xcellent, 10 = poor) at 7:30 a.m.
on the morning after every experimental night, with a
higher score indicating poorer habitual sleep quality.
State anxiety level was assessed at 7:30 a.m. on the
morning after every experimental nights. In our study,
Spielberger State Anxiety Inventory (SAI) was chosen
because it provides evaluation of state anxiety levels,
nam ely a temporary unpleasant emotional arousal in the
face of threatening demands or dangers [23]. Subjects
rated their feelings of anxiety on a four-point scale ranging
from one (almost never anxious) to four (almost always
anxious), a higher score indicating a higher anxiety level.
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On the morning after the NL night, subjects were
asked to assess the effects of simulated ICU noise and
light on sleep disruption, using a five-point scale ranging
from one (no disruption) to five (significant disruption).
Subjec ts were asked to evaluate the comfort, effective-
ness and ease o f use of e arplugs and eye masks on the
morning after the NLEE night, using a five-point scale
ranging from one (very uncomfortable, very unhelpful,
very awkward) to five (very comfortable, very helpful,
very ea sy to use) with low scores indicating a less plea-
sant experience.
Statistical analysis
Data were analyzed using SPSS version 16.0 (SPSS Inc.,
Chicago, IL, USA). Data for the adaptation night were
excluded from analysis bec ause the first night of sleep in
a sleep laboratory room with unfamiliar surroundings dif-
fers from sleep on subsequent nights [24]. All data were
expressed as mean ± standard deviation. One-way
repeated measures analysis of variance (ANOVA) were
used to determine differences in sleep variables, 6-SMT
and cortisol c oncentrations, perceived sleep quality and
anxiety levels during the three nights of the experiment.
Paired student’s t-test or non-parametric Wilcoxon’s
rank sum test were performed to evaluate the effect of
earplugs and eye mas ks on sleep variables and hormones
secretion during exposure to simulated ICU sound and
light where appropriate. Paired sample test was also used
to analyze differences in sound levels between NL and
NLEE nights. An alpha of 0.05 was considered significant.
Results
Fifteen healthy volunteers were recruited. One was
excluded due to evidence of significant insomnia.
A total of 14 subjects (8 females and 6 males, aged 21
to 70 years, mean 31.07 ± 15.64 years) completed the
study. The earplugs and eye masks were applie d easily
and remained intact during NLEE nights.
Sleep architecture
Results of sleep variables during basel ine, NL and NLEE
nights are shown in Table 1. Repeated measures
ANOVA showed that sleep architecture changed signifi-
cantly in percentage of REM sl eep (P =0.03),REM
latency (P = 0.02) and arousal index (P = 0.03) by condi-
tion. Contrast of sleep variables during exposure to
simulated ICU environment indicated tha t use of ear-
plugs and eye masks resulted in more REM sleep
(P = 0.005), shorter REM latency (P = 0.013) and fewer
arousals (P = 0.04; Figure 2).
Urinary excretion of 6-SMT and cortisol
Subjects’ urinary excretion during baseline, NL
and NLEE nights of 6-SMT and cortisol is shown in
Figures 3 and 4, respectively. Dif ferences in nocturnal
urinary secretion levels of 6-SMT (F =7.84,P =0.007)
and cortisol (F = 9.26, P = 0.004) were both significant.
Wilcoxon’s rank sum test showed significant differ-
ences in urine 6-SMT levels for NL and NLEE nights
(Z = -3.17, P = 0.002). But no difference was found in
urine cortisol levels for NL an d NLEE nights (Z = -1.47,
P = 0.14).
Subjective sleep quality and anxiety levels
The results of repeated measures ANOVA for subjective
sleep quality were significant (F = 20.6, P =0.00),but
those for anxiety levels (F =3.55,P =0.06)werenot
(Table 2).
Paired co ntrast showed use of earplugs and eye masks
improved perceived sleep quality notably (P = 0.001).
No difference was founded in anxiety levels between
the NL and NLEE nights (P = 0.28) by paired contrast,
although SAI scores showed interesting trends that
scores for NL night were highest.
Subjective perception of ICU environment and
interventions
On baseline, NL and NLEE nights, sound levels averaged
34 ± 0.6, 66.1 ± 4.2 a nd 66 ± 5.3 dB(A), respectively.
Paired contrast revealed no significant d ifference in the
noise l evel for NL a nd NLEE nights (P = 0.94). Table 3
shows t he subjective percept ion of t he effect of nois e
and light stimuli on sleep disruption on the NL night.
Eleven subjects perceived noise factor as a l ittle disrup-
tion but were able to fall asleep, two perceived n oise as
some disruption and were sometime s unable to fall
sleep, and one perceived light sleep and was easily awa-
kened by noise. There were eight, one and five subjects
perceived a little disruption but were a ble to fall asleep,
some disruption and was sometimes unable to f all
asleep, and light sleep and were easily awakened by con-
stant lighting, respectively.
Subjects’ evaluation of earplugs and eye masks is listed
in Table 4. Overall, they rated the devices highly, as very
comfortable, very helpful and very easy to use.
Discussion
These results support the notion that sleep and hor-
mones are both disturbed w ith exposure to simulated
ICU noise and light in healthy subjects. Use of earplugs
and eye masks improve subjective sleep quality
noticeably.
Our results confirm that subjects not only have poorer
perceived sleep quality, but also suffer from sleep dis-
ruption, measured as more light sleep, longer REM
latency and less REM sleep, with exposure to simulated
ICU noise and light levels. The results are similar to
those reported by Topf and Davis [25] and Wall ace and
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Table 1 Sleep architecture and study condition for subjects (n = 14)
Variable Baseline NL NLEE ANOVA P Contrast P
Time in bed (min) 539.7 ± 1.7 536.0 ± 15.9 536.0 ± 13.7 0.48 ——
Total sleep time (min) 456.0 ± 39.9 454.7 ± 41.8 475.1 ± 33.4 0.20 0.06
Sleep efficiency
Index
0.8 ± 0.1 0.8 ± 0.1 0.9 ± 0.0 0.12 0.09
REM% 10.9 ± 5.9 9.3 ± 4.3 12.9 ± 4.3 0.03 0.005
S1% 21.8 ± 10.4 23.4 ± 11.9 22.5 ± 9.7 0.80 0.67
S2% 43.9 ± 10.2 45.6 ± 10.3 43.5 ± 6.9 0.57 0.20
S3% 14.0 ± 6.8 11.6 ± 6.5 13.9 ± 5.6 0.30 0.11
Sleep onset latency (min) 22.3 ± 13.1 23.4 ± 16.6 15.4 ± 16.4 0.46 0.055
REM latency (min) 121.8 ± 47.0 146.9 ± 56.2 105.7 ± 47.0 0.02 0.013
Arousals index 13.0 ± 4.7 15.1 ± 6.2 12.2 ± 6.5 0.03 0.04
ANOVA, repeated measures analysis of variance; Contrast, paired student’s test or wilcoxon’s rank sum test of simulated ICU environment with and without
earplugs and eye masks; NL, recorded ICU noise and light exposure; NLEE, recorded ICU noise and light, subjects wore earplugs and eye masks; REM, rapid eye
movement.
Figure 2 Example of sleep histograms from the same subject.Lessrapideyemovement(REM)time,longerREMlatencyasexposure
to recorded ICU noise and light. NL, recorded ICU noise and light exposure; NLEE, recorded ICU noise and light, subjects wore earplugs
and eye masks.
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Figure 3 Urinary excretion of 6-SMT for different study conditions . Nocturnal urine 6-SMT concentration dur ing baseline, NL and NLEE
nights were 26.5 ± 20.0, 15.1 ± 13.6, and 22.3 ± 22.9 μg/kg, respectively. 6-SMT, 6-sulphatoxymelatonin; NL, recorded ICU noise and light
exposure; NLEE, recorded ICU noise and light, subjects wore earplugs and eye masks.
Figure 4 Urinary excretion of cortisol for different study conditions. Nocturnal urine cortisol concentration during baseline, NL and NLEE
nights were 2.0 ± 1.6, 4.0 ± 2.4, and 3.2 ± 2.1 μg/kg, respectively. NL, recorded ICU noise and light exposure; NLEE, recorded ICU noise and
light, subjects wore earplugs and eye masks.
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colleagues [16]. However, our study differs in that we
combined levels of noise and light i n a simulated ICU
environment in a sleep laboratory.
The I CU environment is not conducive to sleep. Sur-
vey studies showed that ICU patients co nsidered exces-
sive noise and bright lights noxious and disrupti ve [26].
Freedman and colleagues reported that nurse interven-
tions were mo re disrupt ive than noise or light [8].
Gabor and colleagues found that noise, light and patient
care activities accounted for less than 30% of nocturnal
arous als and awakenings [10]. Recently Cabello and col-
leagues reported noise accounte d for less than 15% o f
arousals and awakenings in mechanical ventilation
patients [27]. Therefore, noise has proved to be an
important sleep-disruptive factor and has negative phy-
siological and psychological effects on patients, although
it may not be responsible for the majority of the sleep
fragmentation. Recent emphasis has been on noise
reduction and encouraging the dimming of lights over-
night in ICU settings, but control of noise is not always
possible and light s are always present in critical care for
patient observations and patient care ac tivities. There-
fore, we hypothesized t hat use of earplugs and eye
masks may have benefits in some ICU patients with
regards to sleep disturbances.
The tolerability of these interventions is critical. Most
healthy subjects rated earplugs as comforta ble and easy
to use [16]. In our study, six subjects rated earplugs as
comfortable and 10 rated eye masks as comfortable, and
allsubjectsusedthemeasilyandkeptthemintactdur-
ing the study nights. However, previous studies showed
that some ICU patients were unwilling to use the ear-
plugs and/or eye masks because they found the inter-
ventions uncomfortable [28]. Some patients commented
that there was a feeling of heat, tightness, sore ears,
claustrophobia and still being a ble to hear when using
earplugs [15,29]. The reasons for this may include
improper inse rtion, individu al var iability in sensitivity or
anatomy of the ears, unsuitable type of earplugs and eye
masks and the a nxious state of patients. Future studies
should consider the sleep intervention according to
patients’ tolerability and explore other methods when
patients can not tolerate the devices. Light disturbances
may be ‘blocked’ by other means and exclusion of blue
light at night by pat ients wearing g lasses that filter out
this light wavelength or nocturnal lighting sources with-
out blue light may be alternatives with regard to mini-
mizing adverse effects on the nocturnal melatonin surge.
In addition, critical care nurses should patiently provide
accurate instruction and assistance for use of earplugs
and eye masks, which may help mor e patients to benefit
from the use of the earplugs and eye masks to promote
better sleep [29].
Previous studies consistently found ICU patients suf-
fered from severe sleep disruption, with a n increased
percentage of wakefulness and stage 1 sleep and a
decrease or absence of both slow wave sleep and REM
sleep [1-3]. Our study indicates a significant difference
in PSG of percentage of REM sleep, REM latency and
arousal index b etween NL and NLEE. Although percen-
tage of REM sleep (12.9%) was statistically significantly
higher in the NLEE period, t he absolute figure in NL
(9.3%) period is still high compared with that frequently
reported in ICU patient PSG studies in which REM per-
centage is often less than 5% [1,2]. Our study cannot
completely simulate the ICU scenario; the healthy
volunteers slept relatively well in a sleep laboratory
while ICU patients are exposed to many other physical
and psychological stressors during their acute illness,
which may also contribute to their sleep disturbance.
Table 3 Subjective perception of sleep disruption (n = 14)
No disruption A little disruption but able to
fall asleep
Sometimes unable to
fall sleep
Light sleep, easy be
awakened
Significant disruption, awake
all night
Noise 0 11 2 1 0
Light 0 8 1 5 0
Table 4 Evaluation of earplugs and eye masks (n = 14)
Helpful to sleep promotion Comfortable Effective for noise/light reduction Easy to apply
Earplugs 6 6 10 11
Eye masks 8 10 13 14
Table 2 Subjective assessment of sleep quality and state anxiety by condition
Baseline night NL night NLEE night ANOVA P Contrast P
State anxiety 28.7 ± 6.3 32.5 ± 5.6 29.8 ± 6.4 0.06 0.28
Sleep quality 1.7 ± 1.3 4.1 ± 1.7 2.3 ± 1.3 0.00 0.001
ANOVA, repeated measures analysis of variance; Contrast, paired student’s test or wilcoxon’s rank sum test of simulated ICU environment with and without
earplugs and eye masks; NL, recorded ICU noise and light exposure; NLEE, recorded ICU noise and light, subjects wore earplugs and eye masks.
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Melatonin is the key circadian regulatory hormone in
humans. Cortisol is an important stress hormone. Mela-
tonin se cretion normally increases at night and decreases
in the early morning hours. In contrast, cortisol secretion
falls. Both are biological markers of the circadian rhythm.
Melatonin therapy has been shown to be ef fective in the
resetting of sleep-wake cycles, the entrainment of circa-
dian rhythms and the treatment of ch ronic insomnia
[30,31]. The melatonin secretion pattern has been related
to the sleep disturbances observed in the ICU [13,14].
Recently there has been some evidence that exogenous
melatonin is effective in improving s leep in ICU patients
[28,32]. Sleep intervention should be extended to a coor-
dinated exogenous melatonin therapy with bright light
[28]. Friese suggested that lighting could be coupled with
shielding o f patient’s eyes to allow for a sufficiently lit
environment so ICU staff could carry out necessary
nighttime activit ies and minimize retinal stimulation for
the patients [33]. Most previous studies evaluated the
effects of earplugs, and recently two studies indicated
that earplugs and eye ma sks w ere a relatively che ap wa y
to improve sleep quality in critically ill patients [15,34].
In fact, our study found that subjects disliked light as
much as noise and eye masks are better than ear plugs in
terms of the subject’s tolerability.
In addi tion, our finding of significantly higher co rtisol
levels when exposure to ICU noise and light agreed with
previous results that acute noise stress invokes the stress
response and high levels of stress hormones [35].
Limitations of the study and suggestions for future
studies
Our study design has a number of limitations, which
should be reviewed. First, the study w as performed in a
sleep laboratory with healthy subjects rather than in an
ICU set ting of critically ill patients, and therefore could
not completely simulate the full auditory and visual
experience of the ICU. Second, the study was only per-
formed for a nine-hour nocturnal period rather than
over 24 hours. T he ICU pat ients experienc e circadian
rhythm disturbances with sleep traversing the day and
night. Therefore, an ideal study should measure the
sleep in healthy volunteers lying recumbent over a 24-
hour period to completely simulate the ICU scenario.
Our study combined noise and light as e nvironmental
stimuli and used earplugs and eye masks as intervention,
so we were unable to measure the effect of each one
separately on sleep and hormones secretion. Further stu-
dies are needed to elucidate the separate mechanisms of
ICU noise and light on sleep disturbance and hormones
secretion. In addition, our sample sizes were small,
which limited the power of our statistical analyses.
Future studies with larger and more diversity of the par-
ticipants would likely support these recommendations.
Conclusions
In summary, our results found that use of earplugs and
eye masks in subjects not only improves subjective sleep
quality, but also incr eases the amount of REM sleep and
nocturnal melatonin levels in a simulated ICU environ-
ment. Our pilot study provides a reasonable basis for
promoting the use of earplugs and eye masks for ICU
patients. Sleep is a b asic human need, sleep disruption
may contribute to patient morbidity and degenerate
quality of life [4,5]. Therefore, we recommend the rou-
tine use of earplugs and eye masks in all ICU patients
even though some patients may b e undergoing o ngoing
disease processes. Future studies should be designed to
determine if t he use of earplugs and eye masks will
improve the sleep quality and ultimately benefit the clin-
ical outcome of critically ill patients.
Key messages
• Subjects had poorer perceived sleep quality, more
light sleep, longer REM latency, and less REM sleep
when exposed to simulated ICU noise and light.
• Nocturnal melatonin and c ortisol secretion levels
differed significantly by experimental condition.
• Use of earplugs and eye masks r esulted in more
REM time, shorter REM latency, less arousal and an ele-
vation of nocturnal melatonin levels.
Abbreviations
6-SMT: 6-sulphatoxymelatonin; ANOVA: analysis of variance; CCU: coronary
care unit; CHin EMG: sub-mental electromyogram; CSICU: cardiac surgical
ICU; EEG: electroencephalogram; ELISA: enzyme-linked immunosorbent assay;
MICU: medical ICU; NL: recorded ICU noise and light exposure; NLEE: NL plus
use of earplugs and eye masks; PSG: polysomnography; PSQI: Pittsburgh
Sleep Quality Index; RAI: radioimmunoassay; REM: rapid eye movement; SICU:
surgical ICU; STAI: Spielberger State-Trait Anxiety Inventory.
Acknowledgements
Thanks are due to Ms Wang Wanyu, Ms Lin yuanjian, Ms Zeng jing, Zhang
Yixiang MD, and Li Yueping MD for their support to the study. The authors
also thank the referees for their careful review of the manuscript.
Author details
1
School of Nursing, Fujian Medical University, Jiaotong Road 88, Fuzhou,
350004, PR China.
2
Sleep-Breath Disorders Center, Second Affiliated Hospital,
Zhongshan Road 34, Quanzhou, 362000, PR China.
3
Department of Nuclear
Medicine, Fujian Province Hospital, East Street 134, Fuzhou, 350001,
PR China.
Authors’ contributions
JX and ZY designed the study, and participated in the coordination and
writing of the manuscript. HR performed data collection, data entry,
statistical analysis and wrote the manuscript. CX participated in the data
collection, data entry, and statistical analysis. ZY was responsible for analysis
of the levels of 6-SMT and cortisol.
Competing interests
The authors declare that they have no competing interests.
Received: 2 October 2009 Revised: 23 December 2009
Accepted: 18 April 2010 Published: 18 April 2010
Hu et al. Critical Care 2010, 14:R66
http://ccforum.com/content/14/2/R66
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doi:10.1186/cc8965
Cite this article as: Hu et al.: Effects of earplugs and eye masks on
nocturnal sleep, melatonin and cortisol in a simulated intensive care
unit environment. Critical Care 2010 14:R66.
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Hu et al. Critical Care 2010, 14:R66
http://ccforum.com/content/14/2/R66
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