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Systematic Review

The impact of environmental risk factors on delirium and benefits of noise and light modifications: a scoping review

[version 1; peer review: 2 approved with reservations]
PUBLISHED 29 Sep 2020
Author details Author details
OPEN PEER REVIEW
REVIEWER STATUS

Abstract

Background: To explore existing literature on the association between environmental risk factors and delirium, and to investigate the effectiveness of environmental modifications on prevention or management of delirium.
Methods: This is a scoping review of peer-reviewed studies in PubMed and the reference lists of reviewed articles. Observational studies reporting the effect of noise, light, and circadian rhythm on delirium and interventional studies assessing delirium in modified environments were reviewed.
Results: 37 studies were included, 21 of which evaluated the impact of environment on delirium and 16 studied possible solutions to mitigate those impacts. Mixed findings of the reviewed studies yielded inconclusive results; a clearly delineated association between high noise levels, abnormal amounts of light exposure, and sleep disruption with delirium could not be established. The environmental interventions targeted reducing noise exposure, improving daytime and mitigating night-time light exposure to follow circadian rhythm, and promoting sleep. The overall evidence supporting effectiveness of environmental interventions was also of a low confidence; however, quiet-time protocols, earplugs, and bright light therapy showed a benefit for prevention or management of delirium.
Conclusions: Environmental modifications are non-invasive, risk-free, and low-cost strategies that may be beneficial in preventing and managing delirium, especially when used as part of a multi-component plan. However, given the limited evidence-based conclusions, further high-quality and larger studies focusing on environmental modifications and delirium outcomes are strongly recommended.

Keywords

delirium, environmental intervention, noise, light, circadian, scoping review

Introduction

Delirium is a multifactorial, acute, confusional state characterized by disturbance of consciousness and cognition; it is particularly common in the intensive care unit (ICU) with incidence of 19 to 87% with higher rates in mechanically ventilated patients13. ICU delirium is associated with adverse outcomes, including prolonged mechanical ventilation, increased risk of long-term cognitive dysfunction, prolonged hospitalization, higher cost of care, and increased mortality47. While the pathophysiology of delirium is poorly understood, there are multiple factors associated with increased risk of delirium including age, education, pre-existing conditions such as hypertension, neurological or psychological disorders, illness severity, Acute Physiology and Chronic Health Evaluation II (APACHE II) score, sensory impairment, and use of analgesics, sedatives, and polypharmacy812. The ICU environment may be a modifiable risk factor for delirium. Decreased natural daylight, night-time light exposure, excessive noise, immobilization, and isolation are potential delirium risk factors in ICU1315.

ICU noise levels are above the World Health Organization’s (WHO) recommendations, which suggest 30 A-weighted decibels (dBA) for background noise, a maximum of 35 dBA for treatment and observation areas, and a maximum of 40 dBA at night1618. Patients interviewed post-ICU discharge report noise as an overall stressor and contributor to loss of sleep19,20. Another common environmental disturbance for ICUs is non-cycling light sources. Disruptions in normal amounts of blue light (460–480 nm) hitting the retina affect neurological processes responsible for melatonin release15. Constant delivery of these wavelengths may cause abnormal suppression of melatonin, altering circadian cycles15. Although the ICU does not lend itself to quietude, it is feasible to employ noise-reducing techniques and light modifications that synchronize circadian rhythm, facilitating recovery.

The prevalence of delirium-associated adverse health effects and the multitude of risk factors in the ICU make delirium prevention and management essential. Current strategies include pharmacological, non-pharmacological, and multi-component interventions geared towards decreasing delirium incidence and duration. Pharmacological interventions focus on haloperidol and dexmedetomidine, with limited research into ramelteon, melatonin, and ziprasidone2124. The largest clinical trial to date on haloperidol or ziprasidone in delirious patients failed to show significant clinical benefit23, and current literature does not support use of anti-psychotic agents, benzodiazepines, or melatonin in delirium management2125. Given the lack of evidence supporting pharmacological measures, research into efficacy of non-pharmacological techniques is crucial. Implementing effective delirium management strategies shows promise in decreasing morbidity, mortality, length of stay, and resource burden in the ICU2. The purpose of this scoping review is to examine the extent and nature of available literature, and highlight areas requiring further inquiry regarding these questions: “How do environmental noise, light, and disrupted circadian rhythms affect delirium?” and “How do existing environmental interventions such as noise reduction, light modifications, and sleep promotion help prevent or manage delirium?”

Methods

This review was conducted according to the methods of Arksey and O’Malley26 and Levac et al.27, and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Extension for Scoping Reviews (extended data)28,29. The aim of this review is to map existing literature identifying modifiable environmental risk factors for delirium, and assess the role of non-pharmacological noise, light, and circadian rhythm interventions for delirium prevention and management.

Search strategy and data charting

Studies were identified by searching PubMed for articles relating to our questions. Search results were restricted to the English language and peer-reviewed studies, with no restriction on year of publication. The search was last executed on November 20, 2019 in order to cover recent publications. Search queries were generated using the following combination of keywords: [“delirium” AND “noise OR sound OR light OR circadian”]. The search was applied with no field tags to maximize results.

After compiling research results and removing duplicates, HH and JL screened titles and abstracts to retrieve articles for eligibility. Articles on pediatric populations, animal subjects, case reports, or where the full-text was unavailable were excluded. Additional studies were identified through hand-searches and searching the reference list of reviewed articles. Disagreements on study eligibility were resolved by involving a third reviewer and a discussion between the reviewers. HH, JC, and JL reviewed the full text of eligible articles and extracted data using a pre-designed worksheet reviewed and tested by the team before data charting (Table 1). Elements of the data charting worksheet included study design, setting, sample size, aim, detailed methodology, characteristics of intervention and control groups, measured outcomes, diagnostic tools, main conclusions, and study strengths and limitations. Disagreements were resolved by discussion.

Table 1. Data extraction sheet.

Study detailsAuthor/Year:
Country:
Study Title:
Study characteristicsStudy design:
Study setting:
Study period:
ParticipantsNumber of subjects:
Include Number of subject per study vs control groups
if available)
Inclusion & exclusion criteria:
Age/gender/Mechanically ventilation status:
Was a history of any cognitive disorders or presence
of delirium considered?
(Please add details if yes)
Study aimStudy aim
Method details
(observational and
interventional studies)
Details of study method, main assessed factors, and outcome
Delirium diagnostic tools & criteria:
(note if not validated)
Sleep quality measurement tools:
(note if not validated)
Noise levels measurement details:
Light levels measurement details:
Follow up length/timing:
Method details
(interventional studies)
Number of study groups:
Control Group Characteristics:
Interventional Group Characteristics:
Intervention details:
(Protocol development, Time of intervention, duration
of intervention)
OutcomesList of measured outcomes:
Significant outcomes and statistics:
Non-significant outcomes:
Adherence rates:
Study featuresStrengths/limitations:
Review list of referencesAdded studies for further review:

We included observational studies analyzing the association between noise levels, light exposure or disrupted circadian rhythm and delirium, and interventional studies assessing the effectiveness of modified noise or light exposure or improved circadian rhythm on delirium. Articles were excluded if environmental intervention was an element of a multi-component non-pharmacological bundle, not the main focus. In the initial full text review and data charting, we reviewed all interventional articles reporting results on delirium or the environmental risk factors of delirium, including noise or light levels, and quality/quantity of sleep. We acknowledge these outcomes are modifiable risk factors linked to delirium prevention or management; however, we excluded articles without results linked to delirium.

Results

Literature search results & outcome

The electronic database search retrieved 457 articles, which were screened by title and abstract, resulting in 166 studies for full-text review. Hand-search and the searching of reference lists added 28 additional articles. During the full-text review of these 194 articles, 157 were excluded. In total 37 studies were included: 21 assessed association between environmental risk factors and delirium13,19,20,3047, and 16 reported on delirium after an environmental intervention7,14,15,18,4859 (Figure 1).

42ca20a9-bf6f-4586-86af-57108c55e135_figure1.gif

Figure 1. PRISMA record screening flow chart.

Characteristics of the reviewed articles

Included studies were conducted between 1997 to 2019, in the USA19,31,37,39,43,46,58,59, the Netherlands14,32,48,50,51, Japan38,41,52,53, France33,36,57, Belgium13,49, Denmark15,34, Italy42,47, Sweden18,20, Canada35, China45, India40, Israel30, Singapore55, South Korea54, Thailand56, Turkey44, and the UK7. Of these, 31 studies were conducted among critically ill patients while five reviewed general hospital populations30,35,41,44,54, and one a geriatric monitoring unit for acute delirium care55. Among the 37 reviewed articles, all observational association studies and 12 interventional studies reported delirium incidence, while two interventional studies measured delirium prevalence18,58. Delirium severity was assessed in three interventional studies48,54,55. Three articles reviewed delirium duration7,48,51.

Most studies assessed delirium using the Confusion Assessment Method for the ICU (CAM-ICU)7,15,18,19,34,36,37,39,40,42,4548,51,5659; other identification methods included the validated Dutch CAM-ICU32, Confusion Assessment Method (CAM)41,50,55, Intensive Care Delirium Screening Checklist (ICDSC)14,33,43, Neelon and Champagne Confusion Scale (NEECHAM)13,49, non-validated52 and validated53 Japanese NEECHAM, Delirium Observation Screening Scale (DOSS)50, behavioral observations based on the Diagnostic and Statistical Manual of Mental Disorders, 3rd edition (DSM-III)35, 3rd edition-revised (DSM-III-R)38, and 4th Edition (DSM-IV)20,41,44, and behavioral observations based on International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) criteria30. One study used both retrospective chart review and site-specific pre-specified criteria based on new and rapid onset of disturbed consciousness and/or perceptual disturbances31. Studies assessed delirium severity by non-validated Delirium Severity Index (DSI)48, Delirium Rating Scale (DRS)54, Delirium Rating Scale-Revised-98 (DRS-R-98)55, and Memorial Delirium Assessment Scale (MDAS)54. Details, including study design, setting, sample size, methodology, outcomes, and findings with statistics are summarized in Table 2 to Table 4 for observational studies reporting on environmental risk factors, and Table 5 to Table 7 for environmental intervention studies.

Effect of environmental risk factors on delirium

Of the observational studies, two analyzed for an association between delirium and noise19,20, five for light13,3033, 12 for sleep3445, and two evaluated multiple factors46,47. Study populations ranged from 7 to 6660 participants, and the majority were done in an ICU (17 of 21)13,19,3134,3640,42,43,4547. The remaining studies did not specify a ward30,35,41,44. Study details and statistical results are in Table 2Table 4.

Noise. Although ICU noise is a suggested predictor for delirium development, two of the three investigating studies found no significant association between ICU noise levels and delirium development19,20 (Table 2). One study assessed A-weighted sound levels with subjective patient reports on ICU noise20. They found no correlation between A-weighted equivalent continuous (LAeq) or maximum (LAmax) noise pressure levels and delirium, while patients’ responses about ICU sounds spread evenly over a spectrum from scary to non-disturbing20. In comparison, Knauert et al.19 evaluated equivalent continuous sound pressure level (Leq) and peak sound occurrences for both A-weighted and C-weighted measurements, finding no correlation with delirium development. There are no industry-standard recommendations for C-weighted levels, but LAeq and LAmax values from both studies were higher than recommended by the WHO17,19,20. In contrast, a study by Davoudi et al.46 assessing the associations between delirium and multiple environmental factors, found average night-time sound pressure levels were significantly higher for patients with delirium46. However, they did not provide exact decibel measurements, likely because they were reporting preliminary findings for a larger cohort study unpublished at the time of this review46.

Table 2. Summary of characteristics and findings of observational studies on association between delirium and noise.

Study
(author,
year,
country)
Study designStudy setting
Population
Subjects
characteristics
Examined risk
factors
Method detailsFindingsStatistics
Noise
Johansson
2012
Sweden20
Observational,
pre-study
ICU (general
medical-
surgical)

n=13
ICU patients
excluding head
injury, hearing
impairment,
dementia
A-weighted
decibel
measurements

Post-ICU survey
on memories of
ICU environment
Delirium: hourly
behavioral
observations by
nurse based on
Granberg-Axell
protocol (2001) and
DSM-IV

Noise: Bruel
& Kjaer 2260
sound level
meter placed
close to patient
bed, one-minute
average interval
of A-weighted
sound levels
analyzed with
B&K Evaluator
software

Memory survey:
open-ended,
unstructured
interview after
ICU discharge
focusing on
memories of ICU
environment
and sounds
No association
between high
number of early
signs of ICU delirium
and high sound
levels

Interview responses:
mixed, some
sound memories
were scary/
irritating, others
were comforting, unnoticed, or
incorporated into
dreams
p > 0.05 for all
noise and
delirium
analyses

No statistics
reported for
interviews.
Knauert,
2016
USA19
Observational,
prospective
MICU

n=59
Adult patients
admitted within
48 hrs before
next sound
recording
period,
excluding those
expected to die
within 24 hrs,
undergoing
comfort care,
or expected to
be transferred
before study
completion
Leq & frequency
of peak
occurrences
Delirium: CAM-ICU
daily

Noise: two Extech
HD600 sound
meters placed at
foot of patient bed
with standardized
distance from care
equipment, 10-
second interval of
A- and C-weighted
sound levels,
decibel range
set to 30-130 dB,
detector response
set to ‘fast, 125
milliseconds’
Delirium was not
associated with Leq
or peak occurrences
p > 0.05 for all
noise and delirium
analyses
Multiple factors including noise
Davoudi,
2019
USA46
Observational,
prospective
pilot
SICU

n=22
All adult patients
expected to stay
in ICU more
than 2 days and
able to wear an
ActiGraph device
Sound pressure
levels

Light intensity

Sleep quality
Delirium:
CAM-ICU
daily, defined as
being delirious
throughout study
period

Noise: iPod
with a sound
pressure
recording
application
measured in dB,
device placed
on wall behind
patient bed

Light: ActiGraph
sensor placed
on wall behind
patient bed at
height of patient
head

Sleep: Freedman Sleep
Questionnaire
daily
Significant higher
average night-
time noise levels in
delirious patients

Light levels were
significantly different
between delirious
and non-delirious
patients

No statistical
association between
overall quality of
sleep and delirium,
but delirious patients
were significantly
more likely to report
difficulty falling
asleep and to find
lighting disruptive at
night
Noise
p < 0.05

Light
p < 0.05

Ability to fall
asleep
p = 0.01

Whether
night-time
lighting was
disruptive
p = 0.04

>p > 0.05 for
all other
sleep and
delirium
analyses

Abbreviations: CAM-ICU: Confusion Assessment Method for the Intensive Care Unit; CI: confidence interval; dB: decibel; DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, 4th Edition; hrs: Hours; ICU: intensive care unit; Leq: equivalent continuous sound pressure level; MICU: medical intensive care unit; RASS: Richmond Agitation and Sedation Scale; RRR: relative risk ratio; SICU: surgical intensive care unit; X2: chi-squared test.

Light. Abnormal lighting cycles are another suggested contributor to delirium60. Seven reviewed studies considered exposure to natural sunlight and relationships with delirium13,3033,46,47 (Table 3). There were two approaches to analysis: effects of windows on delirium incidence13,31 ,33,46,47 and association with admission season46,47. Findings were mixed, suggesting no easily provable relationship between natural light exposure and delirium occurrence. Two window and one seasonal study found no statistical association between delirium and windows or season of admission/duration of preadmission sunlight exposure, respectively3133. Kohn et al.31 compared windowed versus non-windowed rooms in the medical ICU, and natural versus industrial window views in the surgical ICU.31. They also investigated impact of half-sized versus full-sized windows, finding no association between delirium incidence and any of these factors31. Similarly, Smonig et al. found no difference in delirium incidence between patients admitted to windowed versus non-windowed rooms while proving windowed rooms retained natural circadian light variations and non-windowed rooms did not33. In the seasonal study, Simons et al. investigated the effect of admission season on delirium incidence and found no correlation32. A simultaneous assessment found no correlation between preadmission cumulative sunlight exposure and delirium incidence for three photoperiods (7, 28, and 60 days pre-hospital admission)32.

In comparison to studies showing no association between natural sunlight exposure and delirium occurrence, three window studies and one seasonal study found a significant correlation13,30,46,47. In the window studies, Simeone et al.47 associated the lack of natural sunlight with delirium while Van Rompaey et al.13 found an absence of visible daylight led to higher risk of delirium. Davoudi et al.46 examined the pervasive sensing of ICU patients, finding that the measured light intensity in windowed rooms was significantly different between patients with and without delirium46. Additionally, a study on seasonal impact on delirium diagnosis by Balan et al. found a higher incidence of delirium among patients admitted in winter compared to summer30.

Table 3. Summary of characteristics and findings of observational studies on association between delirium and light.

Study
(author,
year,
country)
Study designStudy setting
Population
Subjects
characteristics
Examined risk
factors
Method detailsFindingsStatistics
Light
Balan
2001
Israel30
Observational,
retrospective
Geriatric hospital

n=234
Patients aged ≥65,
with no pre-existing
delirium or unable to
communicate due to
cognitive impairment
Season of delirium
diagnosis
Delirium: ICD-9-CM criteria, assessed and
diagnosed by a psychiatrist after development
of any abrupt change in mental or behavioral
condition

Light: patients compared by season of
admission (winter, December-February;
summer, June-August)
Significantly higher
rates of delirium in
winter than summer
months
X2, 2 df = 14.36
p < 0.001
Kohn
2013
USA31
Observational,
retrospective
MICU

n=6336
All admitted patients,
restricted to the index
ICU admission during a
hospitalization
Presence of a
window

Whether view out
of the window
was a natural or
industrial view

Presence of a
half- or full-sized
window for
windows facing the
same direction
Delirium, MICU: retrospective chart review
of random patient sample (7%); diagnosed
if specific keywords associated with delirium
were documented by physician or nurse on at
least 2 separate days

Delirium, SICU: screened daily by nurse
practitioner for pre-specified criteria based
on new and rapid onset of disturbed
consciousness and/or perceptual disturbance

Windows, both units: whether patient was
admitted to room with or without a window;
whether window had a natural or industrial
view; whether window was half- or full-sized
No association with
delirium incidence
and the presence of a
window, in all analyses

No association with
delirium incidence
and a natural or
industrial view, in all
analyses

No association
between delirium
incidence and
presence of a half- or
full-sized window for
windows facing the
same direction, in all
analyses
p > 0.05 for all
light and delirium
analyses
SICU

n=6660
All admitted patients,
restricted to the index
ICU admission during a
hospitalization
Simons
2014
Netherlands32
Observational,
retrospective
ICU

n=3198
All patients who were
admitted to the ICU
within 30 days of
hospital admission,
restricted to the first
ICU admission during a
hospitalization
7-, 28-, and 60-
day prehospital
photoperiod

Season of
admission

Subgroup
analysis: 28-day
photoperiod in
patients admitted
to ICU within 48
hrs of hospital
admission
Delirium: Dutch validated CAM-ICU at least
twice daily during complete ICU stay

Light: sunlight data was obtained from
nearby weather stations of the Royal
Dutch Meteorological Institute; cumulative
photoperiod was calculated from the total
amount of radiation, defined as total number of
hours of daylight for 7, 28, and 60 days before
hospital admission
No association
between delirium
incidence and
prehospital sunlight
exposure for all
photoperiods (7-, 28-,
60-day)

No association
between delirium
incidence and season
of admission

Subgroup analysis: no
association between
28-day photoperiod
and delirium
incidence
p > 0.05 for all light,
season, and delirium
analyses
Smonig
2019
France33
Observational,
prospective
MICU

n=195
Consecutive adult
patients requiring
nvasive MV in the ICU
for at least 2 days,
without acute brain
injury or conditions
interfering with
delirium assessment
(i.e. dementia, deaf,
blind)
Presence of a
window
Delirium: RASS followed by ICDSC twice daily,
defined as the presence of ICDSC ≥4 for at
least 2 consecutive ICU days

Light: exposure determined by whether
patient was assigned to a room with or without
windows
No association
between exposure to
windows and delirium
burden (incidence
and duration), even
when excluding room
transfers
p > 0.05 for all
light and delirium
analyses
van Rompaey
2009
Belgium13
Observational,
prospective
ICU (mixed)

n=523
All consecutive patients
aged ≥ 18 years with
ICU stay of ≥ 24 hrs;
patients were enrolled
when GCS reached at
least 10.
Absence of visible
daylight
Delirium: NEECHAM Confusion Scale (frequency
not specified)

Light: exposure determined by whether patient
was exposed to visible daylight during ICU stay
Patients had a
significantly higher
risk of developing
delirium with the
absence of visible
daylight
Univariate
OR 1.75
95% CI (1.19-2.56)
p = 0.003

Multivariate
OR 2.39
95% CI (1.28-4.45)
Multiple factors including light
Davoudi
2019
USA46
Observational,
prospective
pilot
SICU

n=22
All adult
patients
expected to stay
in ICU more
than 2 days and
able to wear
an ActiGraph
device
Sound pressure
levels

Light intensity

Sleep quality
Delirium: CAM-ICU daily, defined as being
delirious throughout study period

Noise: iPod with
a sound pressure
recording
application
measured in dB,
device placed on
wall behind patient
bed

Light: ActiGraph
sensor placed on
wall behind patient
bed at height of
patient head

Sleep:
Freedman Sleep
Questionnaire daily
Significant higher
average night-
time noise levels in
delirious patients

Light levels were
significantly different
between delirious and
non-delirious patients

No statistical
association between
overall quality of
sleep and delirium,
but delirious patients
were significantly
more likely to report
difficulty falling asleep
and to find lighting
disruptive at night
Sound
p < 0.05

Light
p < 0.05

Ability to fall
asleep
p = 0.01

Whether night-
time lighting was
disruptive
p = 0.04

p > 0.05 for all
other sleep and
delirium analyses
Simeone
2018
Italy47
Observational,
correlational
SICU (cardiac)

n=89
All patients aged ≥ 18
years who underwent
cardiac surgery with
ICU stay longer than
24 hrs, excluding
history of psychologic
disease or psychogenic
drug use, visual
disturbances, hearing
disorder, RASS ≤ 4
Exposure to
natural sunlight

Presence of a sleep
disorder
Delirium: RASS followed by CAM-ICU

Light: whether patient was exposed to natural
sunlight

Sleep: whether patient has pre-existing sleep
disorder
Significantly more
patients with delirium
were not in a location
with sunlight

Significantly more
patients with delirium
had a sleep disorder
Light, univariate
X2 = 9.737, p = 0.32
Light, multivariate
RRR 0.367, 95% CI
(0.090-1.494), p =
0.034

Sleep, univariate
X2 = 13.934, p <
0.001

Sleep, multivariate
RRR 5.493, 95% CI
(1.255-24.047)
p = 0.024

Abbreviations: CAM-ICU: Confusion Assessment Method for the Intensive Care Unit; CI: confidence interval; dB: decibel; df: degrees of freedom; GCS: Glasgow Coma Scale; hrs: hours; ICD-9-CM: International Classification of Diseases, Ninth Revision, Clinical Modification; ICDSC: Intensive Care Delirium Screening Checklist; ICU: intensive care unit; MICU: medical intensive care unit; MV: mechanical ventilation; NEECHAM: Neelon and Champagne Confusion Scale; OR: odds ratio; RASS: Richmond Agitation and Sedation Scale; RRR: relative risk ratio; SICU: surgical intensive care unit; X2: chi-squared test.

Sleep. Disrupted sleep-wake cycles are associated with altered mental states in hospitalized patients, and are connected with delirium61. In this review, 14 studies19,3438,4047 assessed sleep and delirium with two main methodologies: objective measurements of physiological sleep phases and subjective reports by staff or patient. Five studies objectively measured sleep quality using overnight polysomnography (PSG) or a Zeo wireless sleep monitor19,34,36,42,43, while eight assessed staff reports of behavioral observations and/or self-reports by patients34,35,37,38,41,4547. One study compared both methods33, and two did not specify the measurement method.40,44 (Table 4).

Similar to the articles on natural light exposure, association studies for sleep and delirium have mixed findings, but lean towards disrupted sleep being a delirium predictor. Six of 14 studies found no relationship between sleep and delirium: two PSG studies19,34, three using subjective measures34, and one with an unspecified method37,40,46. One study found no difference in the rate of delirium between patients with typical and atypical sleep on PSG39, while another by Boesen et al. also found no difference in atypical PSG results between patients who did or did not develop delirium34. They compared PSG results with clinical behavioral observations and were only able to ascertain that the more pathological the patient and electroencephalogram findings, the less association with observed sleep34. A study using the Richards-Campbell Sleep Questionnaire (RCSQ) found no significant correlation between perceived sleep quality and delirium, nor any significant relationship when asking how disruptive noise was to sleep37. The study by Davoudi et al.46 used the Freedman Sleep Questionnaire and found no correlation between overall sleep quality and delirium, although they noted patients with delirium were more likely to have difficulty falling asleep and find night-time lighting disruptive46. The last study did not detail their methodology, but found delirium was not significantly related to sleep deprivation40.

Of the nine studies showing statistical correlation between sleep and delirium, three used electronic sleep monitoring36,42,43, five subjective survey measures35,41,45,47,62 and one did not specify the methodology used44. One study found atypical sleep on PSG was significantly tied to increased delirium, while another PSG study found delirium was associated with severe rapid eye movement (REM) reduction36,42. A third study used a novel sleep monitoring device and found a relationship between a lack of REM sleep and delirium43. Their results must be taken in the context of the device being commercially unavailable (Zeo wireless sleep monitor), and the authors not reporting statistical analyses. Among the remaining positive correlational studies, two had patients self-report sleep satisfaction and quality and both saw significantly poorer responses when comparing patients who developed delirium with those who did not35,45. Two studies involved nursing staff observing clinical behaviors and found sleep disturbances were positively linked to higher likelihood of developing delirium38,41.Two studies found an association between delirium incidence and sleep deprivation (methodology not specified)44, and between sleeping disorders and delirium development47.

Table 4. Summary of characteristics and findings of observational studies on association between delirium and sleep.

Study
(author,
year,
country)
Study designStudy setting
Population
Subjects characteristics
Examined
risk factors
Method detailsFindingsStatistics
Sleep
Boesen
2016
Denmark34
Observational,
prospective
descriptive
ICU (mixed)

n=14
Mechanically ventilated
patients aged ≥ 18, without
structural neurological illnesses
or administration of propofol
or benzodiazepines
PSG results

Sleep as
recorded by
CBO
Delirium: SAS & CAM-ICU once/
shift

Sleep, PSG: 24 hour simplified
PSG with a 2-lead-frontal EEG,
2-lead EOG, 1 chin EMG, and
1-lead ECG; recording started
at noon; PSGs were scored
by an EEG technician in 30
second epochs according to
the AASM standards; due to
encephalopathy, wakefulness was
interpreted using eye-blinking
and EEG reactivity

Sleep, CBO: registering 24
hour clinical sleep by attending
nurses, noted on a case report
form as “asleep” or “awake”;
measurements included total
clinical time awake, or asleep,
and number of hours with logged
entries
No clear differences in sleep
patterns for both PSG and CBO
analysis

Less correlation with clinically
observed sleep in more
pathological EEGs and patients

Sleep quality and quantity
cannot be feasibly assessed
with PSG in MV patients, since
the vast majority of PSGs were
atypical with no objective sleep
signs
p > 0.05 for all
sleep and delirium
nalyses
Bowman
1997
Canada35
Observational,
descriptive
Teaching hospital

n=43
Elderly (age not specified)
undergoing orthopedic hip
surgery without dementia or
MMSE score ≤ 23
Sleep
satisfaction
Delirium: DSM-III diagnosis by RN
reports, chart review, interview
with RNs, or assessment by
researcher in daily rounds; MMSE
repeated daily until an score of
≥24

Sleep: 5 days of previous night’s
sleep satisfaction recorded every
AM by a seven-point Likert scale
Patients who developed post-
operative delirium had poorer
sleep satisfaction than those
without post-operative delirium,
except postoperative day 5
Day 2, p = 0.008574
Day 3, p = 0.031772
p > 0.05 for all other
sleep and delirium
analyses
Drouot
2012
France36
Observational,
retrospective
MICU

n=57
Adult, conscious, non-sedated
patients with acute respiratory
failure treated with NIV for at
least 2 days, without GCS < 15,
any CNS disorder, delirium,
confusion, sleep or EEG
interfering drugs in last 48 hrs
PSG resultsDelirium: CAM-ICU daily

Sleep: Embla S700 digital
recorder from 1500 to 0800 on
the following day; leads included:
three EEG channels, chin EMG,
two EOGs, submental EMG,
two tibialis anterior EMGs, and
ECG; EEG signals amplified and
recorded at 200-Hz sampling
frequency, filtered (0.5–70 Hz);
Rechtschaffen and Kales criteria
were used to score sleep stages
and awakenings
Significant association between
delirium occurrence and atypical
sleep on EEG
p < 0.05
Kamdar
2015
USA37
Secondary
analysis of
prospective
observational
study
MICU

n=223
Patients with ≥1 MICU night
in between 2 days of delirium
assessment
Perceived
sleep quality
Delirium: CAM-ICU twice daily at
0800 and 2000

Sleep: RCSQ daily with an
additional item to evaluate
perceived night-time noise
No association between
transition to delirium and
perceived sleep quality
p > 0.05 for all
sleep and delirium
analyses
Kaneko
1997
Japan38
ObservationalHCU
n=36
Patients aged>70 undergoing
gastrointestinal surgery
Sleep-cycle
disturbance
Delirium: DSM-III-R (frequency
not specified)
Sleep: clinical behavioral
observations on sleep &
wakefulness recorded in 2 blocks
(0600-1800, 1800-0600)
Postoperative abnormal sleep
patterns are significantly
associated with development of
delirium
p < 0.05
Knauert
2014
USA39
Observational,
cross-section
pilot
MICU

n=29
Adults admitted to the MICU
for less than 72 hrs without
terminal illness, coma, deep
sedation, severe agitation, or
anatomic contraindications to
PSG evaluation
Atypical sleep
on PSG
Delirium: CAM-ICU on day of
enrollment and during PSG
(frequency not specified)

Sleep: unattended PSG for up
to 24 hrs via Compumedics’
Safiro Portable Data Acquisition
System; initiated in the evening;
leads included: 6 EEG channels,
chin EMG, right and left EOG;
ECG; 200 Hz sampling frequency
and filtered (0.5 - 70 Hz);
Compumedics’ Profusion 2
software
No significant relationship
between delirium incidence and
atypical sleep
p > 0.05 for all
sleep and delirium
analyses
Kumar
2017
India40
Observational,
pilot prospective
derivation
cohort
SICU (cardiac)

n=120
consecutive cardiac surgical
adult patients without delirium
or deafness
Sleep
deprivation
Delirium: assessed once daily
with RASS followed by CAM-ICU
starting on day of extubation

Sleep: method of measurement
not specified
Sleep deprivation was not
significantly related to delirium
p > 0.05 for all
sleep and delirium
analyses
Shigeta
2001
Japan41
ObservationalGeneral hospital

n=29
Patients undergoing
laparotomy for digestive
disease
Sleep
disturbances
Delirium: CAM followed by DSM-
IV diagnosis

Sleep: subjects’ sleep was
monitored every 2 hrs for 5 days
after surgery
All delirious patients had sleep
disturbances with a reversal of
the diurnal sleep cycle, including
delayed sleep onset, frequent
waking, and increased daytime
sleep
No statistics
reported.
Trompeo
2011
Italy42
ObservationalICU

n=29
Patients aged 18-75 with
≥2 days of MV for surgery-
related respiratory failure,
with no psychosis, mental
retardation, stroke, central
sleep apnea, drug or alcohol
abuse, dementia, Alzheimer, or
Parkinson
PSG resultsDelirium: CAM-ICU twice daily

Sleep: NPB-Mallinckrodt
Sandman PSG done from 2200-
0800, scored using Rechtschaffen
and Kales criteria
Delirium is independently
associated with severe REM
sleep reduction
p = 0.002
Whitcomb
2013
USA43
Observational,
pilot
MICU (pulmonary)

n=7
65 years or older, intubated &
sedated, without a diagnosis
preventing mental awareness
assessment
Sleep stages Delirium: ICDSC once daily

Sleep: Zeo wireless sleep
monitor, dry silver-coated fabric
headband sensor with single
bipolar channel, signal includes
EEG/ EOG/ EMG, captured at
128 samples/second and filtered
to a frequency of 2- 47 Hz,
microprocessor reports the sleep
stage every 30 seconds in real
time via artificial neural network
using a reduced set of sleep
stages including wakefulness,
REM, light sleep (stages 1 & 2),
and deep sleep (stages 3 & 4)
Preliminary results suggest a
relationship between lack of
REM sleep and delirium
No statistics
reported.
Yildizeli
2005
Turkey44
Observational,
retrospective
General hospital
n=432
Patients >18 years old
admitted for thoracotomy or
sternotomy with an expected
stay of 2 or more days
Sleep
deprivation
Delirium: once delirium
symptoms were first noted, a
psychiatric consult determined
diagnosis based on DSM-IV
criteria

Sleep: method of measurement
not specified
Univariate and multivariate
analyses showed a significant
association between delirium
incidence and sleep deprivation
Univariate, p =
0.008
Multivariate, OR
5.642, p = 0.05
Zhang
2015
China45
Observational,
prospective
cohort
ICU (cardiovascular)

n=249
adult, post-CABG patients
without preoperative
diagnoses of delirium, mental
disease, or dementia
Quality of
sleep
Delirium: assessed three times
daily (0800, 1600, 2400) with
RASS followed by CAM-ICU, and
if patient developed change in
mental status

Sleep quality: assessed via patient
self-report, poor quality was
defined by symptoms of sleep
disorder or deprivation
Poor sleep quality was the
strongest independent
predictor of delirium
Univariate, p <
0.001
Multivariate, OR
5.001, 95% CI
(2.476-10.101), p <
0.0001
Multiple factors including sleep
Davoudi
2019
USA46
Observational,
prospective pilot
SICU

n=22
All adult patients expected to
stay in ICU more than 2 days
and able to wear an ActiGraph
device
Sound
pressure
levels

Light intensity

Sleep quality
Delirium: CAM-ICU daily, defined
as being delirious throughout
study period

Noise: iPod with a sound
pressure recording application
measured in dB, device placed on
wall behind patient bed

Light: ActiGraph sensor placed on
wall behind patient bed at height
of patient head
Sleep: Freedman Sleep
Questionnaire daily
Significant higher average
of night-time noise levels in
delirious patients

Significant different light levels
in delirious group

No statistical association
between overall quality of sleep
and delirium, but delirious
patients were significantly more
likely to report difficulty falling
asleep and to find lighting
disruptive at night
Noise, p < 0.05
Light, p < 0.05
Ability to fall asleep,
p = 0.01
Whether night-
time lighting was
disruptive, p = 0.04
p > 0.05 for all other
sleep and delirium
analyses
Simeone
2018
Italy47
Observational,
correlational
SICU (cardiac)

n=89
All patients aged ≥ 18 years
who underwent cardiac
surgery with ICU stay longer
than 24 hrs, excluding history
of psychologic disease or
psychogenic drug use, visual
disturbances, hearing disorder,
RASS ≤ 4
Exposure
to natural
sunlight

Presence of a
sleep disorder
Delirium: RASS followed by CAM-
ICU

Light: whether patient was
exposed to natural sunlight
Sleep: whether patient has pre-
existing sleep disorder
Significantly more patients with
delirium were not in a location
with sunlight

Significantly more patients with
delirium had a sleep disorder
Light, univariate
X2 = 9.737, p = 0.32
Light, multivariate
RRR 0.367, 95% CI
(0.090-1.494),
p = 0.034
Sleep, univariate
X2 = 13.934, p <
0.001
Sleep, multivariate
RRR 5.493, 95% CI
(1.255-24.047)
p = 0.024

Abbreviations: AASM: American Academy of Sleep Medicine; CABG: coronary artery bypass graft; CAM: Confusion Assessment Method; CAM-ICU: Confusion Assessment Method for the Intensive Care Unit; CBO: clinical behavioral observation; CI: confidence interval; CNS: central nervous system; dB: decibel; DSM-III: Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition; DSM-III-R: Diagnostic and Statistical Manual of Mental Disorders, 3rd Edition, Revised; DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, 4th Edition; ECG: electrocardiography; EEG: electroencephalography; EMG: electromyography; EOG: electrooculography; GCS: Glasgow Coma Scale; HCU: high intensive care unit; hrs: hours; Hz: Hertz; ICDSC: Intensive Care Delirium Screening Checklist; ICU: intensive care unit; MICU: medical intensive care unit; MMSE: Mini-Mental State Examination; MV: mechanical ventilation; NIV: non-invasive ventilation; OR: odds ratio; PSG: polysomnography; RASS: Richmond Agitation and Sedation Scale; RCSQ: Richards-Campbell Sleep Questionnaire; REM: rapid eye movement; RN: registered nurse; RRR: relative risk ratio; SAS: Riker Sedation-Agitation Scale; SICU: surgical intensive care unit X2: chi-squared test.

Effect of environmental interventions on delirium prevention and treatment

In total, 16 studies evaluated the effects of a modified environment on delirium prevention or management7,14,15,18,4859 (Table 5Table 7). Half were randomized control trials (RCT)18,49,5154,56,57, while half used different study designs including: before-after7,14,48,59, retrospective cohort15,50, and prospective cohort55,58. Sample sizes varied from 11 to 748. Interventions focused on controlling environmental risk factors, including noise and light exposure, disrupted circadian rhythm, and sleep (Figure 2). We categorized these interventions into four modification types: architectural design18,48, environmental noise14,49, environmental light15,5057, and environmental modification bundles with noise and light components7,5759. A summary of environmental interventions on delirium and reported statistical results are presented in Table 8. The interventional articles with results on delirium modifiable risk factors such as noise, light, and sleep were excluded if they did not assess delirium as an outcome. Table 9 represents list of these excluded studies.

42ca20a9-bf6f-4586-86af-57108c55e135_figure2.gif

Figure 2. Environmental risk factors for delirium, and the mitigation strategies.

Architectural design. Two studies18,47 explored a modified ICU design. One study altered the acoustics of the ICU18, whereas the other used a multi-aspect architectural design intervention48. Results were mixed, but subtly suggest the benefit of architectural designs that consider acoustic features (Table 5). Zaal et al.48 assessed patient outcomes in a multi-bed ICU room with less natural light and more noise exposure versus a private room with improved daylight and reduced noise by sound absorbers, glass sliding doors, optimized alarms, and remotely controlled monitors. There was no effect on delirium incidence or severity, but they found a reduction of delirious days in the study group by 0.4 (95% confidence interval (CI) 0.1–0.7, p = 0.005). Another quasi-randomized feasibility study18 conducted noise reduction by refurbishing an ICU room. They installed a wall-to-wall drop ceiling, low frequency sound absorbers, and used a visually plain design. Implementing the noise reduction strategies was deemed feasible, requiring improvements in noise measurements and delirium assessments. Given the small sample size (n=31) and feasibility nature of the study, no further statistical analysis of outcomes was performed; Delirium developed in 33% (2/6) versus 25% (5/25) of study versus control patients. There was a slight reduction in noise reverberation and increase in speech clarity in the modified room, though sound levels remained higher than the WHO recommendations17.

Table 5. Summary of characteristics and findings of interventional studies modifying architectural design.

Study (Author,
Year, Country)
Study
Purpose
Study DesignStudy setting
Population
Subjects
characteristics
Intervention
Details
Outcomes1
(Methods of
Assessment)
Findings
Architectural design modification
Johansson
2018
Sweden18
To assess
feasibility and
effect of a
modified ICU
room on noise
and delirium
Quasi RCT
(feasibility
study)
ICU (General)

n=31: 25 control,
6 intervention
Adult, ICU stay
≥48 hrs
Modified
ICU room to
control noise:
Installed drop
ceilings with
low frequency
noise absorber,
plain room
design, kept
mobile medical
equipment in
room only if
required
Control group:
same ICU
room with no
modification
Delirium
prevalence
(CAM-ICU)

Level of noise
(Microphone
located 10cm
below ceiling,
and 130-160
cm from wall,
attached to a
sound-card,
recorded 30s
intervals of
A, C, and Z
weighted noise
levels)
Reported study
as feasible
with required
improvement in
randomization,
noise
measurement
process,
and delirium
assessment

No statistical
analysis
performed due
to small sample
size; however
intervention
resulted in
slight lower
reverberation
time and higher
speech clarity
Zaal
2013
Netherlands48
To explore
effect of ICU
environment
on incidence,
and course of
delirium
Pre- post
Intervention
ICU (Mixed)

n=130: 55
control, 75
intervention
Adult, ICU stay
≥24 hrs, excluded
unresponsive
patients (RASS
<-3 or GCS ≤ 8)
in ICU
Single-bed
room ICU with
more daylight
and less noise
exposure:
use of sound
absorbers,
glass sliding
doors,
optimized
alarm system
sending filtered
alarms to staff
cell phones,
remotely
controlled
monitors,
sufficient
daylight with
view, warm
colored room
design
Control group:
multi-bed
room, beds
separated by
curtains
Delirium
incidence, and
duration (CAM-
ICU)

Delirium
severity (non-
validated DSI)

Level of light
(Light-sensor
placed 1m
from bed’s
head, recorded
30s intervals of
light intensity
in Volts)
No significant
effect on
incidence of
delirium, however
decreased
number of days
with delirium

No effect on
severity of
delirium

Increased daylight
exposure, but
no effect on
night-time light
exposure

Abbreviations: CAM-ICU: Confusion Assessment Method for the ICU, DSI: Delirium Severity Index, GCS: Glasgow Coma Scale/Score, hrs: hours, ICU: intensive care unit, RASS: Richmond Agitation and Sedation Scale, RCT: Randomized control trial.

1 Only outcomes of interest including delirium related outcomes, sleep quality, sound pressure levels, and light intensity levels, has listed in this table.

2 Details of measured noise and light, such as devices, location, and frequency has not been discussed in detail in this table.

Noise modification. In this review, there were two approaches to mitigate patient exposure to excessive sound. One was to reduce source noise by utilizing behavioral strategies and device/alarm optimization. The other was noise abatement by earplugs. No studies investigated the impacts of behavioral modification on delirium as an independent intervention, but this strategy was used as part of an environmental modification bundle in four studies7,14,58,59. Earplugs were mostly a component of an environmental bundle7,14,57,58, though one study evaluated the effect of earplugs as a single-component intervention49. One article implemented a combination of behavioral strategies and earplugs to reduce excessive noise14. There were mixed findings across studies with noise modification component(s), but results suggest behavioral strategies and earplugs together might help delirium prevention, particularly as part of a multi-disciplinary program targeting environmental risk factors. However, the implementation of sustained behavioral changes and tolerability of earplugs remain challenges57 (Table 6).

Van de Pol et al.14 analyzed the impact of noise reduction on 421 non-delirious ICU patients in an interrupted time series before-after study. They used earplugs and behavioral strategies, including limited bedside conversations, lowered voices, grouped care activities, optimized alarm settings, and closed doors. Reported noise levels were still higher than the WHO limit post-intervention17, however there was a significant decrease in delirium incidence by 3.7% per time interval (p = 0.02), and reduction in sleep medication usage (p < 0.0001) in the study group. Perceived night-time noise was improved, but with no effect on sleep quality or use of delirium medication. Van Rompaey et al. show associations between environmental noise, sleep perception, and delirium49. They conducted a randomized control trial on 136 non-delirious ICU patients and found use of earplugs (from 2200 to 0600) reduced risk of confusion or delirium by 53% (hazard ratio 0.47, 95% CI 0.27–0.82) and improved sleep perception.

Our full-text review and data extraction appraised articles studying single-component noise control strategies, such as behavioral programs6569, earplugs or noise cancelling headphones7174, and headphones equipped with an alarm filtering system70; however these were not included since they reviewed the impact of interventions on the level of noise or quality of sleep, but delirium was not reported as an outcome (Table 9).

Table 6. Summary of characteristics and findings of interventional studies modifying environmental noise.

Study
(Author, Year,
Country)
Study PurposeStudy
Design
Study Setting
Population
Subjects
Characteristics
Intervention DetailsOutcomes1 (Methods of
Assessment)
Findings
Single-component noise modification interventions
van de Pol
2017
Netherlands14
To test effect
of nocturnal
sound-reduction
protocol
on delirium
incidence and
sleep quality in
ICU
Pre- post
Intervention
(interrupted
time series)
MICU, SICU

n=421: 211 control, 210
intervention
Adult, non-delirious,
RASS<−3 for > 50% of
ICU stay, ICU stay≥24
hrs
Nocturnal sound-reduction
protocol: Lowered staff and
devices noise, clustered
care-activities, closed doors
and earplugs in non-
delirious patients, limited
and clustered care activities
Control group: usual care
Delirium incidence (ICDSC)

Sleep (RCSQ)

Level of noise (Perceived
noise item of RCSQ,
and sound meter with
microphone located near
bed’s head, recorded 1s
intervals of A weighted noise
levels)
Decreased delirium incidence
No improvement in sleep
quality
Reduced perceived night-time
noise. Noise pressure levels
not compared between the
two groups due to unusable
pre-intervention values
Reduced use of sleep
medication, no effect on
delirium medication
Van Rompaey
2012
Belgium49
To evaluate
effect of
sleeping with
earplugs on
prevention of
delirium in ICU
RCTMICU, SICU,
cardiosurgical ICU
n=136: 67 control, 69
intervention
Non-delirious, non-
sedated, non-intubated
adults, GCS≥10, no
dementia, ICU stay >24
hrs
Earplugs during sleep
from 2200 to 0600
Control group: No earplugs
Delirium incidence
(NEECHAM)
Sleep perception (Non-
validated simplified sleep
questionnaire with five
dichotomous questions)
No effect on incidence of
delirium, but reduced risk of
confusion, and increased time
to cognitive disturbance onset
Improved sleep quality
Multi-component environmental interventions including noise reduction components
Demoule
2017
France57
To evaluate
effect of
earplugs and
eye mask on
sleep in ICU
RCTICU (General)
n=43: 28 control, 15
intervention
Adult, non-sedated,
Ramsay Sedation Scale
<3, no history of sleep
or neurological disorder,
sepsis, encephalopathy,
ICU stay >48hr
Earplugs and eye-masks
during sleep from 2200 to
0800
Control group: No earplugs
or eye mask
Delirium incidence (CAM-ICU)
Sleep (PSG on first day of
study, Self-reported sleep
quality by simplified visual
analogue scale (VAS; 10 cm
horizontally) at discharge,
and by Pittsburgh Sleep
Quality Index at day 90)
No effect on delirium
No effect on sleep proportion
of N3, but improved sleep
quality only by increasing
duration of N3 stage and
reducing long awakenings in
compliant subjects.
McAndrew
2016
USA58
To evaluate
effect of
quiet time
on delirium,
sedation level,
and physiologic
measures in MV
patients
Prospective
cohort study
MICU
n=72
Mechanically ventilated
adults until extubated
Quiet time from 1400
to 1600; Dimmed lights,
closed window shades, TVs
off, closed doors, clustered
care-activities
Presence of delirium (CAM-
ICU)

Sleep (Nurse perception
of patient’s sleep by an
investigator created tool with
uninterrupted sleep time,
and overall quality of sleep
questions)
No significant effect on
delirium; however reported no
increase in delirium

Improved sleep perception
moderately

Improved respiratory rates,
and nursing satisfaction of
quiet time protocol
Patel
2014
UK7
To test a non-
pharmacologic
bundle with
environmental
noise and
light reduction
components on
delirium and
sleep
Pre- post
Intervention
MICU, SICU

n=338: 167 control, 171
intervention
Non-delirious, non-
sedated adults with
≥1 ICU night, and no
sleep, or cognitive, or
neurologic disorder
Multidisciplinary
intervention from
2300 to 0700; Limited
bedside conversation,
clustered care-activities,
minimized devices noise
levels, dimmed lights,
earplugs and eye mask,
patient orientation, early
mobilization, and sedation
targets.
Control group: usual care
Delirium incidence and
duration (CAM-ICU)

Sleep quality (RCSQ, and the
Sleep in Intensive Care
Questionnaire)


Level of noise

Level of light

(Two environmental meters
placed centrally; mean level
of noise reported in dB,
illuminance reported in lx)
Decreased delirium incidence
and duration

Increased sleep quality,
decrease daytime sleepiness

Decreased level noise

Decrease level of light
Kamdar
2013
USA59
To determine
impact of a
multi-faceted
quality
improvement
program on ICU
delirium, and
sleep
Pre- post
Intervention
MICU

n=300: 122 control, 178
intervention

Adults with ≥1 ICU
night, and discharge
to an inpatient ward
bed or pending
discharge directly
from ICU; without ≥1
night in another ICU
during admission, any
cognitive disorder, or
alcohol or drug abuse,
cardiac arrest during
admission, any other
ICU discharge>96 hrs
prior to assessment
Multi-faceted sleeping
promotion protocol; 3
additive stages of 1) quiet
time, and realignment
of circadian rhythm, 2)
earplugs, eye-masks,
and soothing music, 3)
pharmacological targets to
reduce sedatives.
Control group: usual care
Delirium incidence (CAM-ICU)

Sleep (RCSQ)
Decreased incidence of
delirium

No effect on quality of sleep
ratings

Abbreviations: CAM-ICU: Confusion Assessment Method for the ICU, dB: decibels, GCS: Glasgow Coma Scale/Score, hrs: hours, ICDSC: Intensive Care Delirium Screening Checklist, ICU: intensive care unit, K: Kelvin, lx: Lux, MV: mechanically ventilated, NEECHAM: Neelon and Champagne Confusion Scale, PSG: Polysomnography, RASS: Richmond Agitation and Sedation Scale, RCSQ: Richards-Campbell Sleep Questionnaire, RCT: Randomized control trial.

1 Only outcomes of interest including delirium related outcomes, sleep quality, sound pressure levels, and light intensity levels, has listed in this table.

2 Details of measured noise and light, such as devices, location, and frequency has not been discussed in detail in this table.

Light modification. Light interventions were implemented in an attempt to realign circadian rhythms by reducing night-time exposure and/or improving natural or artificial daylight exposure (Table 7).

Table 7. Summary of characteristics and findings of interventional studies modifying environmental light.

Study
(Author,
Year,
Country)
Study PurposeStudy DesignStudy Setting

Population

Subjects Characteristics
Intervention DetailsOutcomes1
(Methods of
Assessment)
Findings
Light modification interventions
Estrup
2018
Denmark15
To explore effect
of circadian light
on delirium
Retrospective
cohort study
MICU, SICU

n=183
Non-sedated adults with available
CAM-ICU scores, without any coma:
RASS of -5 or -4, or severe dementia
Circadian Lighting:
Supplemental lighting system
delivered light with strongest
intensity of 4000lx and most
blue component from 0700
to 1200, and minimum of 50lx
at 2030
Control group: Regular
lighting
Delirium Incidence
(CAM-ICU, and use
of Haloperidole)
No effect on incidence
of delirium

Reported age and
dexedetomidine as risk
factors for delirium
Pustjens
2019
Netherlands50
To test effect of
dynamic lighting
on delirium and
Retrospective cohort studyCCU

n=748: 379 control, 369
intervention
Non-sedated adults with ≥ 24 hrs
ICU stay
Circadian Lighting: Ceiling
mounted LED panels
delivered light with color
temperature between
2700 and 6500 K at varying
intensities (peak 750lx)
Control group: Regular
lighting
Delirium incidence
(DOSS, and CAM)
No effect on incidence
of delirium
Simons
2016
Netherlands51
To assess effect of
dynamic lighting
on incidence
and duration of
delirium
RCTMICU, SICU
n=714: 360 control, 354
intervention
Adult, ICU stay>24 hrs, both
intubated and non-intubaed
without impairments preventing
delirium assessments were
included
Artificial high-intensity
dynamic lighting application:
Ceiling mounted fluorescent
tubes delivered light
with alteration in color
temperature and intensity:
blueish-white light up to 4300 K,
and 1700 lx from 0900 to
1600, except intensity of 300
lx from 1130 to 1330
Control group: Usual lighting:
300 lx, 3000 K
Delirium incidence,
and duration (CAM-
ICU)

Level of light
(Photometer placed
at 2m height on
wall near bed’s
head, recorded
15minutes intervals
of light intensity
in lx)
No significant effect on
incidence of delirium, or
number of delirium-free
days

Increased mean
cumulative daytime
lighting
Taguchi
2007
Japan52
To evaluate
effect of BLT on
post-operative
circadian
optimization and
delirium
RCT (Pilot)SICU

n=11: 5 control, 6 intervention
Middle-aged, or aged post-
operative esophageal cancer
patients, with no mental disorders;
randomized after extubation
BLT: 5000lx from 0730 to
0930 for 3 of the post-
operative days, by a self-stand
or a table-top illuminator
Control group: Usual lighting:
600-1000lx
Delirium incidence
(non-validated
Japanese
NEECHAM)

Sleep/Circadian
rhythm (Activity
levels and rhythm
recorded by ankle
accelerometers and
memory heart rate
recorder)
Decreased post-
operative delirium rate
on day 3 of the BLT, but
no overall significant
effect on delirium
incidence

Non-significant decrease
in activity level during
sleep
Ono
2011
Japan53
To evaluate
effect of BLT on
post-operative
circadian
optimization and
delirium
RCT (Pilot)SICU

n=22: 12 control,10 intervention
Adult post-esophagectomy
patients, who anticipated to be
extubated the day after surgery;
randomized after extubation
BLT: 2500 to 5000lx from
0730 to 0930 for 4 days
(0730-0745: 2500lx, 0745-
0800: 4000lx, 0800-0900:
5000lx, 0900-0915: 4000lx,
0915-0930 2500lx), by a self-
standing L-shaped illuminator
to maintain lighting in front of
patient’s face
Control group: usual lighting
Delirium incidence
(Validated Japanese
NEECHAM)

Sleep/Circadian
rhythm (Activity
levels and rhythm
recorded by ankle
accelerometers and
memory heart rate
recorder)
Non-significant lower
rate of post-operative
delirium

Decreased amount of
activity during sleep
on the nights of days 4
and 5
Potharajaroen
2018
Thailand56
To evaluate effect
of BLT on post-
operative delirium
RCTSICU

n=62: 31 control, 31 interventions
Adults aged ≥ 50, with APACHE
II Score ≥ 8 without coma, life-
time history or current delirium,
neuro-degenerative, psychiatric, or
neuroinflammatory disease
BLT: Bright Light therapy,
5000lx from 0900 to 1100 for
3 days, at a distance of 1.40
m from the patient's face
Control group: usual lighting:
500lx
Delirium incidence
(CAM-ICU)

Sleep (Assessing
insomnia by ISI)
Decreased delirium
incidence

Higher ISI score
was associated with
development of
delirium, and BLT
lowered ISI scores.
Yang
2012
South Korea54
To determine
impact of BLT
with antipsychotic
treatment in
delirious patients
Randomized
open parallel
group
Consulting psychiatry division of a
general hospital
n=36: 16 control, 20 intervention
Hospitalized adults with psychiatry
referral, with DRS≥ 12 without any
other axis I disorders on DSM-IV or
antipsychotics or benzodiazepines
use
BLT as adjunctive treatment
with risperidone: 10,000 lx
from 0700 to 0800 for 5 days
by a height-adjustable light
box
Control group: Resperidone
Delirium severity
(DRS, MDAS)

Sleep (Sleep log
with total sleep
time, efficiency,
onset latency,
awake times
questions)
Decreased delirium
severity

Improve total sleep time
and sleep efficiency
Chong
2013
Singapore55
To examine
effect of GMU on
sleep, cognitive,
and functional
outcomes in
delirious patients
Prospective
cohort study
GMU

n=228
Adult delirious patients>65 years
old, without coma, or terminal
illness, or BLT contraindications
(manic disorders, severe eye
disorders, photosensitive skin
disorders, or photosensitizing use)
BLT: 2000- 3000lx from 1800
to 2200 delivered by ceiling
lights in addition to HELP
protocol
Delirium severity
(CAM, DRS-98,
locally validated
CMMSE)

Sleep (Sleep log
with total sleep
time, number
of awakenings,
number and length
of sleep bouts
questions)
No significant effect
on DRS severity scores,
but improved DRS
sleep–wake disturbance
sub-score, No significant
improvement on CMMSE
scores

Improved mean
total sleep time, and
functional status score
Multi-component environmental interventions including light modification components
Demoule
2017
France57
To evaluate effect
of earplugs and
eye mask on sleep
in ICU
RCTICU (General)

n=43: 28 control, 15 intervention
Adult, non-sedated, Ramsay
Sedation Scale <3, no history of
sleep or neurological disorder,
sepsis, encephalopathy, ICU stay
>48 hrs
Earplugs and eye-masks
during sleep from 2200 to
0800
Control group: No earplugs
or eye mask
Delirium incidence
(CAM-ICU)

Sleep (PSG on
first day of study,
Self-reported sleep
quality by simplified
visual analogue
scale (VAS; 10 cm
horizontally) at
discharge, and by
Pittsburgh Sleep
Quality Index at
day 90)
No effect on delirium

No effect on sleep
proportion of N3, but
improved sleep quality
only by increasing
duration of N3 stage
and reducing long
awakenings in compliant
subjects.
McAndrew
2016
USA58
To evaluate
effect of quiet
time on delirium,
sedation level,
and physiologic
measures in MV
patients
Prospective
cohort study
MICU

n=72
Mechanically ventilated adults until
extubated
Quiet time from 1400 to
1600; Dimmed lights, closed
window shades, TVs off,
closed doors, clustered care-
activities
Presence of
delirium (CAM-ICU)

Sleep (Nurse
perception of
patient’s sleep by
an investigator
created tool with
uninterrupted sleep
time, and overall
quality of sleep
questions)
No significant effect
on delirium; however
reported no increase in
delirium

Improved sleep
perception moderately

Improved respiratory
rates, and nursing
satisfaction of quiet time
protocol
Patel
2014
UK7
To test a non-
pharmacologic
bundle with
environmental
noise and
light reduction
components on
delirium and
sleep
Pre- post
Intervention
MICU, SICU

n=338: 167 control, 171
intervention
Non-delirious, non-sedated adults
with ≥1 ICU night, and no sleep, or
cognitive, or neurologic disorder
Multidisciplinary intervention
from 2300 to 0700; Limited
bedside conversation,
clustered care-activities,
minimized devices noise
levels, dimmed lights,
earplugs and eye mask,
patient orientation, early
mobilization, and sedation
targets.
Control group: usual care
Delirium incidence
and duration (CAM-
ICU)

Sleep quality (RCSQ,
and the Sleep in
Intensive Care
Questionnaire)

Level of noise, and
light
(Two environmental
meters placed
centrally; mean level
of noise reported
in dB, illuminance
reported in lx)
Decreased delirium
incidence and duration

Increased sleep quality,
decrease daytime
sleepiness

Decreased level noise

Decrease level of light
Kamdar
2013
USA59
To determine
impact of a multi-
faceted quality
improvement
program on ICU
delirium, and
sleep
Pre- post
Intervention
MICU

n=300; 122 control, 178
intervention
Adults with ≥1 night ICU stay, who
discharged to an inpatient ward
bed or pending discharge from
ICU; without ≥1 night in another
ICU during admission, any cognitive
disorder, alcohol or drug abuse,
cardiac arrest during admission,
any ICU discharge>96 hrs prior to
assessment
Multi-faceted sleeping
promotion protocol; 3
additive stages of 1) quiet
time, and realignment of
circadian rhythm, 2) earplugs,
eye-masks, and soothing
music, 3) pharmacological
targets to reduce sedatives.
Control group: usual care
Delirium incidence
(CAM-ICU)

Sleep (RCSQ)
Decreased incidence of
delirium

No effect on quality of
sleep ratings

Abbreviations: BLT: bright light therapy, CAM: Confusion Assessment Method, CAM-ICU: Confusion Assessment Method for the ICU, CCU: coronary care unit, CMMSE: Chinese Mini–Mental State Examination, dB: decibels, DOSS: Dutch version of the Delirium Observation Screening, DRS: Delirium Rating Scale, DRS-98: Delirium rating scale-R98, DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, GMU: Geriatric Monitoring Unit (A specialized delirium management unit), HELP: Hospital Elder Life Program (standardized protocols to manage cognitive impairment, sleep deprivation, immobility, visual impairment, hearing impairment, and dehydration), hrs: hours, ICU: intensive care unit, ISI: Insomnia Severity Index, K: Kelvin, LED: light-emitting diode, lx: Lux, MDAS: Memorial Delirium Assessment Scale, MV: mechanically ventilated, NEECHAM: Neelon and Champagne Confusion Scale, PSG: Polysomnography, RASS: Richmond Agitation and Sedation Scale, RCSQ: Richards-Campbell Sleep Questionnaire, RCT: Randomized control trial.

1 Only outcomes of interest including delirium related outcomes, sleep quality, sound pressure levels, and light intensity levels, has listed in this table.

2 Details of measured noise and light, such as devices, location, and frequency has not been discussed in detail in this table.

Reduction of nocturnal light exposure

The included articles in this review, studied eye masks7,57,59 and overnight light dimming7,58,59 as part of an environmental modification bundle to reduce night-time light exposure. However, the effects of less nocturnal light exposure on delirium, was not evaluated as a single intervention.

Improving natural daylight exposure

Three observational studies31,33,87 and one before-after study48 investigated improved natural lighting via windows. They compared patient outcomes in rooms with a window or larger-sized windows versus windowless or smaller-sized windows, respectively. No observational studies suggested association between improved natural lighting and delirium31,33,87. Zaal et al.48 demonstrated reduction in delirium duration, comparing patients in private rooms with more natural light versus less bright multi-bed rooms; however, there were no differences in delirium incidence or severity between groups.

Improving artificial daylight exposure

Eight studies examined effect of improved daylight exposure via artificial lighting, of which three used an artificial circadian lighting system15,50,51, and five used bright light therapy (BLT)5256. No study implementing artificial dynamic or circadian lighting revealed significant effects on delirium. BLT studies had mixed results; three studies significantly improved delirium prevention or management, while the other two showed a non-significant tendency to reduce delirium rates.

A retrospective cohort study of 183 non-sedated ICU patients by Estrup et al.15 used a circadian lighting system from 0700 to 2300 which varied in intensity and color temperature. During the morning, light intensity was greatest, up to 4000 lux (lx), and the amount of blue light strongest. As the day progressed, light intensity decreased and color temperature shifted towards warmer tones until no blue light was present. There was no improvement in delirium incidence, and no association between circadian lighting and delirium incidence (odds ratio (OR) 1.14; 95% CI 0.55, 2.37; p = 0.73). Pustjens et al.50 retrospectively studied a cohort of 748 non-sedated patients. They implemented a dynamic lighting system consisting of two ceiling-mounted light-emitting diode (LED) panels which delivered variable intensities of light (peak of 750 lx) with a color temperature between 2700 and 6500 Kelvin (K). There was no effect on delirium incidence. Another RCT by Simons et al.51 measured the effects of a dynamic lighting application (DLA) in 734 ICU patients. DLA was administered through ceiling-mounted fluorescent lights which delivered a variety of bluish-white light from 0700 to 2230 with a maximum intensity of 1700 lx and a maximum temperature of 4300 K between 0900 and 1600, except between 1130 and 1330 when light intensity was 300 lx. This study was terminated early, but preliminary analysis demonstrated delirium incidence of 38% versus 33% in control versus study patients, with no significant improvement on delirium incidence or duration.

Four studies investigated the use of BLT as a single-component intervention to prevent52,53,56 or treat54 delirium, while one study used BLT as an element of a multi-component bundle to manage delirium55. BLT consisted of exposure to high intensity light (2000 to 10000 lx) for one to four hours daily. Three studies used a peak intensity of 5000 lx52,53,56. Taguchi et al.52 conducted a randomization pilot study on 11 post-operative patients, utilizing a daily light intensity of 5000 lx from 0730 to 0930 for days 2 through 5 post-surgery. Delirium assessment scores decreased on day 3 of BLT (p = 0.014), but there was no significant effect on overall delirium incidence (16% versus 40% study versus control group, p = 0.42). In another RCT, Ono et al.53 applied BLT on 22 post-operative patients, for two hours from 0730 to 0930 for four days. Light intensity started at 2500 lx, increasing to 5000 lx, then decreasing to 2500 lx. There was a non-significant tendency towards lower rates of delirium in the study group (1 of 10 patients) versus control group (5 of 12 patients), while BLT significantly reduced the amount of activity during sleep on days 4 and 5. Potharajaroen et al.56 studied 62 post-operative patients by implementing BLT at 5000 lx from 0900 to 1100. Eleven of 31 control patients versus 2 of 31 patients in the intervention group developed delirium. There was a significant association between BLT and decreased delirium incidence (OR 0.12, 95% CI 0.03–0.54, p = 0.005). A study by Yang et al.54 on 36 delirious patients used a higher light intensity (10000 lx) over a shorter period (0700 to 0800). This study investigated the use of BLT as an adjunctive treatment of delirium with risperidone. They found a significant decrease in delirium severity in patients receiving BLT in addition to risperidone (DRS 23.9 ± 4.9 versus 20.6 ± 3.6 in control versus study group, p = 0.03). Chong et al.55 studied 228 delirious elderly patients admitted to a delirium management unit. They incorporated lower intensity BLT as part of their multi-component program, and exposed patients to 2000 to 3000 lx of light for four hours from 1800 to 2200 daily. They reported significant improvement in total sleep time and functional outcomes during treatment of delirious patients.

Intervention bundles (combination of light and noise modification)

Earplugs and eye mask

One reviewed study explored effects of earplugs and an eye mask on delirium57, while two others used earplugs and an eye mask as part of their interventional bundle7,59. All three noted decreased incidence of delirium, but observed different effects on sleep quality. Demoule et al.57 conducted an RCT on 43 non-sedated ICU patients to investigate the impact of sleeping with earplugs and an eye mask from 2200 to 0800 on patient outcomes. They found no improvement in delirium incidence, duration or architecture of sleep in the study group, regardless of patient compliance using the equipment. Although compliant study subjects experienced improved sleep with longer N3 (deeper sleep) duration and a lower number of prolonged awakenings, there was no significant change in delirium incidence. There were several articles in our initial screening reporting improved perceived noise or sleep quality with the use of earplugs and eye masks, however those were excluded since none reported results on delirium7877 (Table 9).

Quiet time, and sleep promotion bundles

Quiet time is a specific amount of time during which modifiable noise and light is actively reduced. Our review included three studies installing quiet time as the single interventional element58 or as a part of a sleep promotion bundle7,59. Core elements of quiet time were behavioral strategies, minimized bedside activity by clustering care, reduced volume of devices/alarms, and dimmed lights7,58,59. The study that implemented daytime quiet time failed to show significant effects on delirium58, while two sleep promotion studies decreased delirium incidence using nocturnal quiet time combined with components such as earplugs, eye masks, and pharmacological targets7,59. Although the multi-component sleep promotion trials decreased delirium incidence, effectiveness of the separate components is unclear.

McAndrew et al.58 applied quiet time from 1400 to 1600 among 72 mechanically ventilated ICU patients. In the 24 hours after starting quiet time, there was no increase in delirium rate and 19% of delirious patients improved to a negative CAM-ICU status. However, there was no significant effect on delirium in their analysis. Quiet time did lead to moderately improved sleep quality and less frequently administered sedatives which helped remove patients from mechanical ventilation. A pre-post research by Patel et al.7 studied a nocturnal multidisciplinary environmental sleep promotion program in 338 non-delirious, non-sedated ICU patients. Their program included nocturnal quiet time with earplugs, eye mask, patient orientation, early mobilization, and sedation targets. The study group showed significant reduction in delirium incidence (by 33% p < 0.001), and a decrease in delirium duration (3.4 ± 1.4 versus 1.2 ± 0.9 days, p = 0.021). Sleep quality and night-time light and noise levels were also improved in the study group, however reported noise levels were still higher than the WHO limits17. They additionally reported a significant association between sleep efficiency and a lower risk of developing delirium (OR 0.90, 95% CI 0.84–0.97). A larger pre-post study (n=300) by Kamdar et al.59 initiated a multi-faceted sleep promotion protocol consisting of three additive stages: 1) nightly quiet time and realignment of circadian rhythm, 2) sleeping with earplugs, eye masks, and soothing music, and 3) pharmacological targets to reduce sedatives. They reported decreased delirium incidence (OR = 0.46, 95% CI 0.23–0.89, p = 0.02) and perceived night-time noise in the study group, but no improvements in sleep quality.

Table 8. Effectiveness of environmental interventions on delirium.

InterventionStudiesDelirium
incidence
Delirium
prevalence
Delirium
duration
Delirium
severity
Statistics
Architectural design modification
Acoustic modified ICU
room
Johansson, 201818--NA1----No analysis done due to small sample size
Private room with less
noise and more light
exposure
Zaal, 201348NSE2--3NSEDelirium incidence: 51% control 45 % intervention, (OR 0.6, 95 % CI
0.3–1.6, p = 0.53)
Delirium duration: Decreased number of days with delirium by 0.4
(95 % CI 0.1–0.7, p = 0.005)
Delirium severity: DSI score per day with delirium, mean (SD):
2.3±0.7 control, 2.5±0.8 intervention, p = 0.34
Noise modification interventions
Sound reduction protocol
(Behavioral strategies
and earplugs)
van de Pol, 201714------Delirium incidence decreased by 3.7% per time period (p = 0.02)
EarplugsVan Rompaey,
201249
NSE, Decreased
risk of confusion
------Delirium incidence: 20% control, 19% intervention
Risk of confusion/ early delirium: decreased by 53% (HR .0.47, 95%
CI 0.27 to 0.82)
Median NEECHAM score: 24 (829) control 26 (5-29) intervention
(Mann-Whitney U, p = 0.04)
Time to cognitive disturbance onset: Increased, p = 0.006
Light modification interventions
Artificial dynamic/
circadian lighting
Estrup, 201815NSE------Delirium incidence: 28% control, 30% intervention, (OR 1.14; 95%
CI 0.55-2.37; p = 0.73)
Pustjens, 201950NSE------Delirium incidence, n(%): 19/379 (5.0) control 20/369 (5.4)
intervention, p = 0.802
Simons, 201651NSE--NSE--Delirium incidence, n(%): 123/373 (33) control 137/361 (38)
intervention, (OR 1.24, 95 % CI 0.92–1.68, p = 0.16)
Delirium duration (hours): 2 (1-5) control, 2 (2-5) intervention, p =
0.87
Bright light therapyTaguchi, 200752NSE, Decreased
delirium scores
on day 3 of BLT
------Delirium incidence: 40% control, 16 % intervention, p = 0.42 by
Fisher’s exact probability test. There was a significant difference in
NEECHAM delirium score between the two groups on the morning
of day 3 of BLT by the Mann—Whitney U-test (p = 0.014)
Ono, 201153NSE------Delirium incidence, n(%): 5/12 (42) control, 1/10 (10) intervention,
p > 0.05
Potharajaroen,
201856
------Delirium incidence, n(%): 11/31 (35) control 2/31 (6) intervention,
(OR 0.12, 95 % CI 0.03–0.54, p = 0.005)
Yang, 201254------DRS score: decreased in study group (F=2.87, p = 0.025)
MDAS score: Not significantly different between the two groups
Chong, 201355------NSE,
Improved
functional
and sleep
outcomes
DRS severity score: decreased by 6.2±6.3 (22.5±5.8 versus 14.6±6.1
in initial versus discharge DRS, p > 0.05)
Environmental modification targeting both noise and light
Earplugs & eye maskDemoule, 201757NSE------Delirium incidence, n(%): 2/22 (6) control 2/23 (7) intervention, p =
1
Quiet timeMcAndrew,
201658
--NSE----No significant effect on delirium scores (p = 0.648)
Multi-component sleep
promotion protocol
Patel, 20147----Delirium incidence, n(%): 55/167 (33) control 24/171 (14)
intervention, (OR 0.33, 95% CI 0.19–0.57, p < 0.001)
Delirium duration (length of time spent delirious), mean ±SD:
3.4±1.4 control, 1.2 ±0.9 intervention, p = 0.021
Improved sleep efficiency index was associated with a lower risk of
developing delirium (OR 0.90, 95% CI 0.84–0.97)
Kamdar, 201359------Incidence of delirium/coma, n (%): 76/110 (69) control, 86/175 (49)
intervention, (OR 0.46; 95% CI 0.23-0.89, p = 0.02)

Daily delirium/coma-free status, n (%): 272/634 (43) control,
399/826 (48) intervention, (OR 1.64, 95% CI, 1.04-2.58, p = 0.03)

Abbreviations: OR: Odds Ratio, CI: Confidence Interval, DSI: Delirium Severity Index, SD: Standard Deviation, HR: Hazard Ratio, NEECHAM: Neelon and Champagne Confusion Scale, BLT: Bright light therapy, DRS: Delirium Rating Scale, MDAS: Memorial Delirium.

1 No statistical analysis was done

2 No significant effect

3 Decreased

Table 9. List of excluded studies investigating impact of environmental interventions on delirium risk factors1.

Study
(author,
year)
Short summaryReason for
exclusion
Architectural design modification to improve environmental noise and light
Gabor
200363
Study aim: To identify high noise and its impact on sleep, and test the effect on noise reduced private
vs multi-bed ICU rooms
Study design, and setting: Observational, MICU & SICU (n= 6 healthy subjects)
Intervention: Healthy subjects spent one night in a private room, and one night in a multi-bed room
Findings: Lower mean and mean maximum noise levels, less noise peaks, improved sleep quantity, no
effect on sleep quality in private room
No delirium
report or
measurement
Luetz
201664
Study aim: To investigate the effect of acoustically modified ICU rooms on noise levels
Study design, and setting: Observational, ICU modified vs standard room
Intervention: Work room behind patient’s head (window to patient room, sound protective materials,
drawers opening from both work and patient rooms, place to keep alarm systems, monitors, and
medical devices), noise-protection side boards between beds, automatic room doors, an LED ceiling
from head to foot of each patient for dynamic lighting.
Findings: Decreased mean and maximum nocturnal noise levels, as well as sound peaks>50 dBA
No delirium
report or
measurement
Environmental noise reduction (behavioral modification)
Kahn
199865
Study aim: To identify sources of noise peaks and effect of behavioral modification on noise reduction
Study design, and setting: Pre-post intervention, MICU
Intervention: Behavioral modification program targeting noise reduction
Findings: Identified talking and televisions as the most noticeable noise origins. The number of noise
peaks and mean peak level of noise decreased by 1.9 dBA after intervention
No delirium report or measurement
Monsén
200566
Study aim: To identify sources of sleep disturbance and effect of behavioral modification on sleep and
noise reduction
Study design, and setting:Pre-post intervention, NICU (n=25)
Intervention: Behavioral modification program targeting noise reduction
Findings: Nursing and medical care were the main causes of sleep disturbance. The intervention
decreased identified sources of sleep disturbance, and partly reduced noise levels.
No delirium
report or
measurement
Crawford
201867
Study aim: To identify sources of noise and effect of behavioral modification on noise reduction
Study design, and setting: Pre-post intervention, MICU
Intervention: Behavioral modification program targeting noise reduction
Findings: No clinical effect on noise reduction (<1.0 dBA). They explained that the reason was due to
respiratory devices, heating, ventilation, and air-conditioning systems being the source of high noise
levels.
No delirium
report or
measurement
Guisasola-
Rabes
201968
Study aim: To evaluate the effect of a sound-activated visual noise-warning system on noise reduction
Study design, and setting: Pre-post intervention, SICU (n=148)
Intervention: Using a visual noise display meter (SoundEar 2 device) with colored visual warnings on
noise levels>55dBA &>60dBA
Findings: Reduction in ambient noise. The reduction was sustained for two weeks after switching off
the device.
No delirium
report or
measurement
Plummer
201969
Study aim: To evaluate the effect of a sound-activated visual noise-warning system on overnight noise
reduction
Study design, and setting: Pre-post intervention, MICU, SICU, NICU
Intervention: Using a visual noise display meter (SoundEar 3 device) with colored visual warnings on
noise levels>55dBA & >60dBA
Findings: Reduction in overnight ambient and peak noise. The reduction was sustained for 4 months
after continued use of device
No delirium
report or
measurement
Environmental noise reduction (alarm noise abatement)
Schlesinger
201770
Study aim: Creation of a wearable frequency-selective silencing device to filter alarm noises
Study design, and setting: Interventional, Simulated ICU setting (n=24 healthy subjects)
Intervention: Noise cancelling headphone with frequency-Selective Silencing Device, filtering alarms
while passing other sounds
Findings: Removed the ICU alarm noise while allowing the patient to hear all other environmental
sounds without distortion
No delirium
report or
measurement
Environmental noise reduction (earplugs)
Wallace
199971
Study aim: To test the effect of earplugs on the sleep of healthy subjects in simulated ICU noise
Study design, and setting: RCT- feasibility, Sleep study center with simulated ICU noise (n=6 healthy
volunteers)
Intervention: Earplugs during sleep
Findings: Improved sleep quality by shorter REM latency and increased REM sleep
No delirium
report or
measurement
Scotto
200972
Study aim: To evaluate the effect of earplugs on sleep
Study design, and setting: Quasi-RCT, MICU, SICU (n=88; 49 control, 39 intervention)
Intervention: Earplugs during sleep
Findings: Improved the perception of sleep
No delirium
report or
measurement
Litton
201773
Study aim: To explore the feasibility, effectiveness, and implementation of earplugs on sleep and
delirium in ventilated patients
Study design, and setting: RCT, SICU, (n=40 intubated patients; 20 control, 20 Intervention)
Intervention: Earplugs (All day when on mechanical ventilation, and during sleep when extubated)
Findings: Earplugs were feasible on the basis of acceptability and protocol compliance with a mean
noise abatement of 10 dB, and a reduced perceived noise level by half. No significant effect on sleep
quality
No delirium
report or
measurement
Gallacher
201774
Study aim: Quantifying the ability of headphones with and without active noise control technology on
noise exposure
Study design, and setting: Pre-post Intervention, ICU-CS (n=3 polystyrene model heads placed in
patient bay)
Intervention: Headphones without and with active noise cancelling system
Findings: Headphones with active noise cancellation resulted in 6.8dB reduction in noise exposure,
and decreased exposure to high intensity sounds
No delirium
report or
measurement
Environmental noise and light reduction (earplugs and eye masks)
Richardson
200775
Study aim: To identify sleep disturbing factors, and test the effectiveness of earplugs and eye masks on
sleep
Study design, and setting: post‐test quasi‐experimental, CTICU, (n=64; 28 control, 34 Intervention)
Intervention: earplugs and eye mask
Findings: Improved sleep while noise was reported as an still a disturbing factor
No delirium
report or
measurement
Hu
201076
Study aim: To investigate the effect of earplugs and eye masks in healthy subjects.
Study design, and setting: Randomized cross-over experimental, Sleep study center with simulated
ICU noise (n=14 healthy volunteers)
Intervention: earplugs and eye masks
Findings: Improved architecture and perceived quality of sleep, and higher night levels of melatonin
No delirium
report or
measurement
Jones
201277
Study aim: To study perceived sleep quality with earplugs and eye masks.
Study design, and setting: Pre-post Intervention, ICU, (n=100; 50 control, 50 Intervention)
Intervention: earplugs and eye masks
Findings: Increased sleep duration but no effect on sleep quality
No delirium
report or
measurement
Le Guen
201478
Study aim: To assess the effect of earplugs and eye masks on the sleep of surgical ICU patients
Study design, and setting: RCT, PACU, (n=41; 21 control, 20 Intervention)
Intervention: earplugs and eye mask
Findings: Preserved sleep quality, decreased the need for daily nap, but no effect on sleep duration
No delirium
report or
measurement
Environmental light modification (Nocturnal light modification)
Albala,
201979
Study aim: To evaluate the effectiveness of using nocturnal blue-depleted lighting pods
Study design, and setting: Non-RCT trial-feasibility study, Non-intensive care medical unit (n= 33
nurses and 21 patients)
Intervention: Reduce nocturnal light exposure by using wireless proximity-sensing, blue-depleted
lights for night-time bed-side tasks
Findings: Use of nocturnal blue-depleted lighting pods for overnight lighting purposes found to be
feasible
No delirium
report or
measurement
Multi-component interventions with environmental noise and light modification components
Walder
200080
Study aim: Effectiveness of nocturnal behavioral rules on ICU light and noise levels
Study design, and setting: Pre-post Intervention, SICU (n=17; 9 pre, 8 post)
Intervention: Nocturnal light and noise reduction (Systematic door closures, lowered staff voice and
alarm noise, less use of direct light, limited care activities).
Findings: Lowered mean light disturbance intensity with a greater variability of light. Decreased the
noise level equivalent, and peak noise level. No effect on background noise level. Decreased estimated
sleep duration and higher number of awakenings.
No delirium
report or
measurement
Olson
200181
Study aim: To examine the efficacy of quiet time on frequency of sleep
Study design, and setting: Pre-post Intervention, NICU (n=239; 118 control, 121 intervention)
Intervention: Quiet time from 0200 to 0400 and 1400 to 1600
Findings: Improved quality of sleep, Reported association between improved sleep and decreased
levels of light and noise
No delirium
report or
measurement
Dennis
201082
Study aim: Effectiveness of the Quiet time protocol on sleep, ICU light and noise levels
Study design, and setting: Pre- post Intervention, ICU (n=50)
Intervention: Quiet time including dimmed lights, lowered staff and devices noise, grouped and
limited care activities, limited family visits from 0200 to 0400 and from 1400 to 1600
Findings: Decreased daytime level of light and noise, improved observed sleep
No delirium
report or
measurement
Bartick
201083
Study aim: Effect of the quiet time protocol on sleep
Study design, and setting: Pre-post Intervention, Non-intensive care, Medical-surgical unit (n=
267;161 pre, 106 post)
Intervention: Somerville Quiet time Protocol from 2200 to 0600; automated lights-off, warning
for noise levels >60dBA, lullaby, minimized staff and care activities, Minimized alarms by following a
bedtime routine program
Findings: Decreased reporting of noise as a sleep disruption factor, decreased need of as needed
overnight sedatives.
No delirium
report or
measurement
Li
201184
Study aim: To study the efficacy of nocturnal noise control on sleep quality in SICU patients
Study design, and setting: Interventional (Quasi-experimental), SICU (n=55; 27 control, 28
intervention)
Intervention: Noise and light control guidelines for sleep
Findings: Improved quality of sleep, and significantly reduced average and peak noise levels
No delirium
report or
measurement
Boyko
201785
Study aim: To investigate the effect of an improved ICU environment on sleep quality of ventilated
patients
Study design, and setting: RCT (cross over design), ICU (n= 17)
Intervention: Quiet protocol from 2200 to 0600
Findings: No significant effect on sleep patterns (measured by polysomnography) or noise levels
No delirium
report or
measurement
Goeren
201886
Study aim: To decrease noise levels by quiet time intervention
Study design, and setting: Interventional (Pre-post Intervention), NSICU (4 location of noise
recording)
Intervention: Dimmed lights, lowered staff and devices noise, quiet time signs, and optional earplugs
and eye masks from 0300 to 0500 and from 1500 to 1700
Findings: Reduced noise levels in 2 of the 4 investigated locations by 10-15 dB
No delirium
report or
measurement

Abbreviations: CTICU: cardiothoracic Intensive care unit, dBA: A-weighted decibel, ICU: intensive care unit, ICU-CS; post cardiac surgery intensive care unit, LED; light-emitting diode, MICU: medical intensive care unit, NICU; neurology intensive care unit, NSICU; neurosurgical intensive care unit, PACU; post-anaesthesia care unit, RCT: randomized control trial, SICU: surgical intensive care unit.

1 This table does not provide complete summary of characteristics and findings of these excluded studies. The purpose of this table is only to present a list of excluded studies investigating impact of environmental interventions on delirium modifiable risk factors. These studies were excluded from this review since no delirium outcome was reported.

Discussion

In this scoping review, the existing literature was searched for studies on the impact of environmental risk factors and interventions on delirium: 21 studies were retrieved reporting the effects of environmental risk factors on delirium and 16 studies reported experiments on possible solutions to modify the environment. Small sample sizes, heterogeneous study methods, and inconsistent results among reviewed studies proved the need for expanding research on the impacts of environmental risk factors and efficacy of mitigations related to delirium.

Modifiable ICU environmental risk factors for delirium

ICUs are high-tech environments with round-the-clock activities that have a negative impact on patients’ experience and clinical outcomes due to excessive noise, light, and disturbed sleep and circadian rhythm13,48,49.

Noise. The WHO set recommendations for hospitals not to exceed an average of 30 dBA or a maximum of 35 dBA in treatment areas (maximum of 40 dBA at night)17. A 2016 study by Hu et al. found average sound levels of 62.8 dB, with a mean level of 59.6 dB between 0000–0700, when investigating sound in various ICUs88. Consistently, five reviewed articles measuring ICU sound pressure with or without noise modification interventions reported levels exceeding the WHO recommendations14,1820.

A 2009 WHO report set night-time noise guidelines and reported on relationships between night-time noise, sleep, and health. According to the report, excessive night-time noise (above 35 dB) disturbs sleep, provokes annoyance and agitation, reduces cognition, impairs communication and comprehension of surroundings, and contributes to psychiatric disorders. The combination of sleep disruption, decreased cognitive function, and lowered comprehension of surroundings associated with high noise levels may contribute to acute confusion and delirium89,90. In our review, two of three observational studies investigating the association between high noise levels and ICU delirium found that high noise levels had no significant effect on delirium incidence19,20. This result is surprising as it has been suspected that noise levels exceeding a normal threshold have detrimental effects on patient recovery, especially with regard to sleep and mental status. It is worth considering the difficulty in assessing the true effect of high noise levels in these two studies. First, there is no available baseline research to compare delirium incidence in high noise level ICUs versus those with statistically lower decibel values. It is possible the threshold for adverse effects is lower or higher than the most recently investigated decibel levels. In addition, Knauert et al.19 mentioned a limitation for their study in the inadequate statistical power to detect differences in decibel level between patient comparisons. For the study by Johansson et al.20, their results need to be taken in context of using a non-validated delirium diagnosis protocol.

Light. During the daytime, normal light intensity is around 10000 lx and recommended night-time light levels conducive to sleep are below 30 lx60. Natural fluctuation of light levels throughout the day contributes to the natural sleep-wake cycle by triggering the release and suppression of melatonin. Alteration of the sleep-wake cycle and a lack of daylight schedule have been shown to be associated with psychiatric diseases60. Daytime light levels in the ICU are below normal daylight levels and above the threshold for sleep disruption at night60. In a study by Hu et al. light intensity was measured over 24 hours near windows, in the center of rooms, and at the eye level of mechanically ventilated patients. Average light intensity at these locations were 425 lx, 191 lx, and 388 lx respectively over 24 hours and 84 lx, 103 lx, and 87 lx between 2401 and 075988. Minimal variation in daytime and night-time light levels disrupts the natural sleep-cycle and may contribute to patients becoming unable to distinguish day from night.

Abnormal natural light cycles are cited in recent literature as a potential modifiable risk factor for delirium management60. Seven studies analyzing the impact of natural light on delirium incidence suggest this element of the ICU lacks a definitive causative relationship with development of the condition. Most of these studies enrolled critically ill patients whose condition gives them a higher likelihood of having consistently closed eyes compared to the general hospital population. It should be considered for future research that these patients’ retinas may not receive the same strength light stimulus as other populations, suggesting the need for ICU-specific lighting strategies. For the two seasonal studies, one found delirium was diagnosed significantly more in the winter than summer30, while the other found exhaustive evidence ruling out a link between delirium and pre-hospital photoperiod exposure year-round32. These findings suggest there are factors aside from seasonal light exposure affecting delirium. Additionally, of the three studies with a positive correlation between exposure to natural daylight or season of admission, the two natural daylight studies had vague descriptions of their measurements of patient’s exposure to natural or artificial light13,47. It is hard to assess whether the patient could have received benefits when the proximity of the stimulus to the patient is unclear.

As with excessive noise levels, further research into abnormal natural lighting cycles is necessary to delineate any threshold for adverse effects to patients’ well-being.

Sleep. Similar to our findings regarding effects of noise and light levels on delirium, reviewed articles on sleep showed mixed results for both forms of measure (electronic sleep monitoring and subjective reports). Recent literature states sleep is disturbed in ICU patients regardless of delirium19,42, and this concern is supported by the fact that unmeasurable sleep was found in non-delirious patients in included PSG studies. It is hard to compare results of included wireless monitoring studies, since different methodologies were used for each study, with different devices, leads, and levels of adherence to American Academy of Sleep Medicine standards. Similarly, it is difficult to compare findings from objective sleep monitoring protocols and subjective survey methods, and these need separate consideration. A major concern in analyzing subject sleep quality in delirious patients is patients with an altered mental state and/or confusion may not answer consistently or truthfully, and measures must be taken to assess whether answers are a correct representation of their condition.

Environmental solutions to prevent or manage delirium

Noise modification. The negative impact of patient exposure to noise led to several studies focusing on noise pollution in the clinical environment. Mitigated exposure to noise levels might promote patient outcomes and staff satisfaction58,91. Noise reduction or abatement strategies include architectural features, behavioral alterations, alarm optimization, earplugs, headphones, and noise cancelling devices. Whilst these strategies have been studied in relation with improved noise levels and sleep promotion (Table 9), further research is required to make evidence-based recommendations for the effect of noise reduction on delirium prevention and treatment.

Implementing ICU designs with acoustic features such as sound absorbers, reversible drawers to open both inside and outside the room, or room designs with the ability to locate alarmed devices or transfer alarms away from the patient, might improve exposure to noise and benefit delirium management48,92,64. Zaal et al. demonstrated a lower delirium duration by modifying ICU design with acoustic considerations, however there was no change in delirium incidence rate48. These strategies require major renovation or early construction planning, and further research is required to confirm cost-effectiveness and clinical benefits.

Staff and family conversations and care-activities are significant sources of ICU noise pollution16,65,66. Although behavioral modification might be ineffective as a single-component intervention67, low-cost adjustments such as limited bedside conversation, lowered voices, clustered care-activities, minimized TV and overhead use and volume, use of vibrating pagers, and visual noise-warning devices may be necessary to achieve better results in sound reduction7,14,65,66,68,69, sleep improvement66, and decreased delirium14. To be successful, continuous awareness, education of staff on the impact of excessive noise exposure, and routine monitoring of implemented strategies is crucial7. Technologies that help staff and visitors recognize excessive noise might complement implementation of behavioral strategies. Visual noise-warning devices display colored warnings at higher levels of noise and can be an effective, sustained noise reduction strategy68,69. Use of noise-warning systems has a greater impact on the reduction of ambient noise compared with peak noise levels68,69. This is likely a result of change in staff behavior after visual warning while having no effect on medical equipment or alarms.

Alarms are a significant source of ICU noise pollution16,65, and a large portion are considered false positives93. Studies show modifying ICU alarms by lowering volume, optimizing device settings, and filtering false alarms may reduce disturbing alarm noise9480. Schlesinger and colleagues equipped wearable earbuds with a frequency-selective silencing device, which could successfully filter ICU alarms while allowing patients to hear and communicate effectively without experiencing the negative consequences of audible alarms70. Optimization of alarms was used as an element of a noise reduction bundle and sleep promotion studies of this scoping review7,14,59.

Abating environmental noise by earplugs or headphones appears feasible and effective to reduce noise and improve sleep in the ICU49,57,7174. Here, one study failed to prove benefits of using earplugs and eye masks during sleep on delirium57, while another earplug trial decreased risk of confusion, and delayed initiation of cognitive disturbances with no significant effect on incidence of delirium49. Given the potential effectiveness and low costs, this method is frequently used in multi-component interventions7,59; however, non-compliancy is an issue in earplugs studies57. A recent meta-analysis91 reported a 13.1% (95% CI, 7.8–25.4) rate of non-compliancy due to intolerance, anxiety, or accidental removal of earplugs. Headphones with active noise cancellation technology might improve patient outcomes by mitigating exposure to noise. Gallacher et al. modeled an experiment by embedding sound meters in the auditory meatus of polystyrene model heads located near patients’ beds in a cardiac ICU74. They demonstrated a significant reduction in overall noise exposure and exposure to high intensity noises using noise cancelling headphones.

Despite inconsistent results of the reviewed studies on efficacy of noise modifications on delirium, this review suggests considering physical design features and multi-component noise reduction programs may benefit delirium prevention or management. This is consistent with current recommendations suggesting multi-component interventions to achieve adequate noise reduction91; Van de Pol et al.14 reduced delirium incidence by implementing a noise reduction program consisting of behavioral strategies, device optimization, and earplugs. However, there is a need for high-quality randomized control trials with larger sample sizes to evaluate efficacy, sustainability, and long-term effects of noise modification interventions with a focus on delirium.

Light modification. Optimized circadian rhythm needs bright days and dark nights. Various light modification strategies have been proposed to follow circadian rhythms. These are categorized as such: decreasing night-time light exposure, and increasing daylight.

Round-the-clock ICU activities make nigh-time light reduction challenging to maintain a level of light sufficient for providing care, but not disturbing sleep. Dimming lights as part of quiet time strategies is effective to mitigate intensity of light during quiet time hours, however, this may cause variation in perceived light and consequently cause sleep disturbance80. Possible solutions are clustering care-activities to reduce bedside interruptions7 and use of portable lighting pods with less blue wavelength during the night79. Whilst the trial of sleep masks and earplugs by Demoule at al.57 failed to show benefit to delirium, eye masks are effective in promoting sleep by light abatement7,78,76,77. However, poor compliance in the use of eye masks due to accidental removal, or anxiety/claustrophobia, and the risk of sensory deprivation in mechanically ventilated patients, remains challenging57.

Environmental modification to increase daylight exposure is possible through the architectural considerations of promoting natural lighting or utilizing artificial illumination. Research into whether windows allow enough light to promote sleep-wake cycles and prevent delirium, and whether seasonal light levels contribute to delirium, has been conducted with inconclusive findings31,33,87. From our results, the greatest interventional effect on delirium was from bright light therapy.

Our review included five studies on BLT, three reporting a significant effect on delirium incidence or severity52,54,56 with sleep promoted in four studies5356. BLT has the greatest effect between 2500 and 10000 lx for 30 to 60 minutes, with a shorter duration for greater intensities of light, when administered either at twilight or dawn to obtain a circadian effect61. The BLT in this review applied 2000 -10000 lx of illuminance for between one and four hours. The use of 2000 lx was effective in improving sleep quantity and functional status during management of delirium as part of a bundle. The use of 5000 lx was associated with decreased delirium incidence in two of three studies and the use of 10000 lx, as an adjunctive treatment with risperidone, was associated with a decrease in delirium severity54. While BLT may help regulate sleep-wake cycles and prevent/treat delirium, research into melatonin secretion and circadian rhythms suggests periods of darkness play as large a role as daytime light levels in promoting sleep and preventing delirium60,95. The importance of light and darkness prompts a need for research into effects of dynamic lighting systems. This review included three studies focused on dynamic lighting among sedated and non-sedated patients, using lighting systems which produced cooler blue light in the mornings and shifted towards warmer tones as the day progressed. The lighting systems produced different levels of intensity throughout the day, reaching a peak of between 750 and 4000 lx and a minimum level of 0 lx. None of these studies showed significant effects on delirium15,50,51; however, they used peak light levels below normal daytime levels.

Maintaining a circadian rhythm, by nocturnal darkness and BLT, as a low-cost, low-risk, easy-to-apply intervention can help improve patient outcomes. Research is required to investigate the use of dynamic lighting with higher peak light intensities or the combination of dynamic lighting and BLT. Additionally, there is a need for defining effective characteristics of light modification strategies for sedated and non-sedated patients. Sedated patients may have disrupted circadian rhythm of melatonin96, and application of light therapies might have limited retina stimuli when eyes are closed. Studies comparing efficacy of light modifications on prevention or treatment of delirium among these two groups of patients, with application of different intensity levels of light in closed-eyes patients, might be of benefit.

Intervention bundles (light and noise modification). There is a growing interest in using quiet time interventions to promote sleep. Quiet time protocols have successfully reduced sound pressure, improved sleep quality, and reduced the use of sedatives80,8183, but effects of quiet time on delirium development needs further research. McAndrew et al. implemented a daily quiet time protocol in ICU patients and reported inconclusive results on delirium scores and moderate improvement in sleep perception58. Two neurocritical ICU studies have implemented a two hour quiet time during day and night81,82. A significant improvement in subjective sleep and increased staff satisfaction was achieved81,82. They reported decreased light by 75–85% and noise by 15%, with results being more significant during day-shift quiet time; this might be due to overall lower levels of nocturnal light and noise82.

Sleep promotion protocols utilize noise and light control strategies with other components, such as patient orientation, early mobilization, medication optimization, and sedation targets to improve sleep in quality and quantity. Here we included two sleep promotion studies reporting results on delirium, however future research is needed to evaluate which component of sleep promotions are effective in reducing delirium. Patel et al.7 significantly improved sleep quality and reduced delirium incidence by implementing a non-pharmacological multidisciplinary sleep program. They raised protocol compliance to > 90% by ongoing education, signage and posters, monitoring, and spot-checking program quality by experienced nurse champions. Interestingly, a large sleep promotion study by Kamdar et al., decreased delirium incidence while there was no effect on sleep59. It is not clear if improvements in delirium are attributable to sleep, emphasizing the need for future studies focused on single interventions or single components of multifaceted interventions with regard to delirium results.

The main strength of this review is synthesizing results of both observational association studies and interventional studies. This approach details a broader picture of the current state of this research field and bridges the gap between establishing correlational relationships and continuation of experimental trials. A major limitation of this review is the narrow search method. By searching one database (Pubmed) and the included articles’ reference lists, there is likely additional literature available to expand our findings, however the authors did a hand search within related journals, Embase, and Google Scholar databases to include existing interventional research articles. Another limitation was that the generated data from reviewed studies did not have full details, and quality of evidence was not evaluated among studies; however, this review was intended to be a literature mapping with limited description of relevant publications.

Conclusions

This review of studies investigating the association between delirium and either high noise levels, abnormal amounts of natural daylight, and/or sleep disruptions did not reveal a clear relationship between delirium and these variables. It is recommended to perform additional research into more comprehensive, but related, risk factors to find a stronger predictor. Additional research could include analyses of specific noise sources or a comparison between overcast, rainy, and sunny times. This review revealed the need for further research targeting the effectiveness of environmental interventions on delirium. Current literature lacks randomized control trials with larger sample sizes to evaluate the efficacy of intervention on delirium and its long-term outcomes. Another knowledge gap is the lack of adequate conclusive research on single-component interventions. The interventional bundle studies lead to uncertainty about which component impacts the result. Given the low-cost and non-invasive nature of environmental modifications and their potential beneficial role in reduction of modifiable risk factors, it is recommended to implement these interventions in current practice, especially as multi-component bundles.

Data availability

Underlying data

All data underlying the results are part of the article and no additional source data are required.

Reporting guidelines

OSF: PRISMA-ScR checklist for ‘The Impact of Environmental Risk Factors on Delirium and Benefits of Noise and Light Modifications: A Scoping Review’. https://doi.org/10.17605/OSF.IO/NHWKA29

Data are available under the terms of the ‘Creative Commons Zero "No rights reserved" data waiver’ (CC0 1.0 Public domain dedication).

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Hashemighouchani H, Cupka J, Lipori J et al. The impact of environmental risk factors on delirium and benefits of noise and light modifications: a scoping review [version 1; peer review: 2 approved with reservations]. F1000Research 2020, 9:1183 (https://doi.org/10.12688/f1000research.25901.1)
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Reviewer Report 16 Jul 2021
Annmarie Hosie, The University of Notre Dame Australia, School of Nursing and Midwifery, Darlinghurst, New South Wales, Australia;  St Vincent's Health Network, Sydney, Australia 
Approved with Reservations
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Thank you for the opportunity to review your manuscript, 'The impact of environmental risk factors on delirium and benefits of noise and light modifications: a scoping review'.

Overall, this is a clearly written manuscript reporting a large ... Continue reading
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Hosie A. Reviewer Report For: The impact of environmental risk factors on delirium and benefits of noise and light modifications: a scoping review [version 1; peer review: 2 approved with reservations]. F1000Research 2020, 9:1183 (https://doi.org/10.5256/f1000research.28584.r88467)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Reviewer Report 09 Mar 2021
Ari Ercole, Division of Anaesthesia, Division of Neurosurgery, University of Cambridge, Cambridge, UK 
Approved with Reservations
VIEWS 22
The authors present a systematic scoping review of the literature studying the impact of environmental risk factors on delirium. This is a potentially important area. Delirium is a problem in healthcare and whilst environmental factors have been implicated, they have ... Continue reading
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Ercole A. Reviewer Report For: The impact of environmental risk factors on delirium and benefits of noise and light modifications: a scoping review [version 1; peer review: 2 approved with reservations]. F1000Research 2020, 9:1183 (https://doi.org/10.5256/f1000research.28584.r79721)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.

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