The Impact of Environmental Risk Factors on Delirium and Benefits of Noise and Light Modifications: A Scoping Review

Purpose: To explore existing literature on the association between environmental risk factors with delirium and to investigate the effectiveness of environmental modifications on prevention or management of delirium. Materials and 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: Thirty eight studies were included, of which, 21 evaluated impact of environment on delirium, and 16 studied the interventions. Interventions targeted reducing noise exposure, improving light exposure to follow circadian rhythm, and promoting sleep. Mixed findings of the reviewed studies yielded to inconclusive results; however quiet-time protocols, earplugs, and bright light therapy might benefit prevention, or management of delirium. Results: Thirty seven 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. Interventions targeted reducing noise exposure, improving day-time 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. Conclusion: 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. Three observational studies 30, 32, 73 and one before-after study 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 delirium 30, 32, 73 demonstrated reduction in delirium duration, comparing patients in private rooms with more natural light versus less bright multi-bed rooms; however, there was no difference in delirium incidence or severity between groups. 32, 73 our results, greatest interventional effect on delirium from bright light therapy. Our review included five studies on BLT, three reporting a significant effect on delirium incidence or severity 51, 53, 55 with sleep promoted in four studies 52-55 . 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 effect 60 . 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 severity 53 . 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 delirium 59, 89 . 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 delirium 15, 49, 50 ; however, they used peak light levels below normal levels.

Included studies were conducted between 1997 to 2019, in the USA 19 Additional records identified through other sources (n =28) 46 . The remaining four studies did not specify a ward and were performed in a general hospital setting 29,34,40,43 . Study details and reported statistical results are in Table 1.

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 development 19,20 . One study assessed A-weighted sound levels with subjective patient reports on ICU noise 20 . 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-disturbing 20 . 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 WHO 17,19,20 . In contrast, a study by Davoudi et al. 45 found average night-time sound pressure levels were significantly higher for patients with delirium 45 . However, they did not provide exact decibel measurements to compare with recommended WHO levels, likely because they were reporting preliminary findings for a larger cohort study unpublished at the time of this review 45 .

Light
Abnormal lighting cycles are another suggested contributor to delirium 59 . Seven of the reviewed studies considered exposure to natural sunlight and any statistical relationships with delirium 13, 29-32, 45, 46 .
There were two approaches to analysis: effects of windows on delirium incidence 13,30,32,45,46 and association with admission season 45,46 . Findings were mixed across the studies, 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, respectively [30][31][32] . Kohn et al. 30 compared windowed versus non-windowed rooms in the medical ICU, and natural versus industrial window views in the surgical ICU. 30 . They also investigated impact of half-sized versus full-sized windows, finding no association between delirium incidence and any of these factors 30 . 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 not 32 . In the seasonal study, Simons et al. investigated effect of admission season with delirium and found no correlation 31 . A simultaneous assessment found no correlation between preadmission cumulative sunlight exposure and delirium incidence for three photoperiods (7,28, and 60 days prehospital admission) 31 .
In comparison to studies showing no association between natural sunlight exposure and delirium occurrence, three window studies and one seasonal study found a significant correlation 13,29,45,46 . In the window studies, Simeone et al. 46 associated lack of natural sunlight with delirium while Van Rompaey et al. 13 found absence of visible daylight led to higher risk of delirium. Davoudi et al. 45 examined pervasive sensing of ICU patients, finding measured light intensity in windowed rooms was significantly different between patients with and without delirium 45 . 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 summer 29 .

Sleep
Disrupted sleep-wake cycles are associated with altered mental state in hospitalized patients, and are connected with delirium 60 . In this review, 14 studies 19, 33-37, 39-46 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 monitor 19,33,35,41,42 , while eight assessed staff reports of behavioral observations and/or self-reports by patients 33,34,36,37,40,[44][45][46] . One study compared both methods [33], and two did not specify their method of measurement, only stating that they evaluated the relationship between sleep deprivation and delirium 39,43 .
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 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) relationship between sleep and delirium: two PSG studies 19,33 , three using subjective measures 33 , and one with unspecified method 36, 39, 45 . One study found no difference in rate of delirium between patients with typical and atypical sleep on PSG 38 , while another by Boesen et al. also found no difference in atypical PSG results between patients who did or did not develop delirium 33 . 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 sleep 33 . 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 sleep 36 .
The study by Davoudi et al. 45 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 disruptive 45 . The last study did not detail their methodology, but found delirium was not significantly related to sleep deprivation 39 .
Of nine studies showing statistical correlation between sleep and delirium, three used electronic sleep monitoring 35,41,42 , five subjective survey measures 34, 40, 44, 46, 61 and one did not specify methodology 43 . One study found atypical sleep on PSG was significantly tied to increased delirium, while another PSG study found delirium was associated with severe REM reduction 35, 41 . A third study used a novel sleep monitoring device and found a relationship between lack of rapid eye movement (REM) sleep and delirium 42 . 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 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 not 34,44 . Two studies used nursing staff observing clinical behaviors and found sleep disturbances were positively linked to higher likelihood of developing delirium 37, 40 . Two studies found an association between delirium incidence and sleep deprivation (methodology not specified) 43 , and between sleeping disorders and delirium development 46 .

Figure2. Environmental Risk Factors for Delirium, and the Mitigation Strategies
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Architectural design
In this review, two of the studies [18,47] explored a modified ICU design. One study altered the acoustical design of the ICU 18 , whereas the other used a multi-aspect architectural design intervention 47 .
Results were mixed, but subtly suggest the benefit of architectural designs that consider acoustic features.
Zaal et al. 47 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 study 18 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. The study deemed feasible, requiring improvements in noise measurements and delirium assessments. Given the small sample size (n=31) and feasibility nature of 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 recommendations 17 .

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 impacts of behavioral modification on delirium as an independent intervention, but this strategy was used as part of an environmental modification bundle in 4 studies 7,14,57,58 . Earplugs were mostly a component of an environmental bundle 7,14,56,57 , though one study evaluated the effect of earplugs as a single-component intervention 48 . One article implemented a combination of behavioral strategies and earplugs to reduce excessive noise 14 . 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 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint targeting environmental risk factors. However, implementation of sustained behavioral changes and tolerability of earplugs remain challenges 56 .
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, minimized alarm volume, and closed room doors. Reported noise levels were still higher than the WHO limit post-intervention 17 , 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 delirium 48 . 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 programs [62][63][64][65][66] , earplugs or noise cancelling headphones [67][68][69][70][71] , and headphones equipped with an alarm filtering system 72 ; 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 (Excluded studies; Supplementary Table 3).

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.

Reduction of nocturnal light exposure
In this review, eye mask use 7,56,58 , and overnight light dimming 7, 57, 58 were encouraged as part of an environmental modification bundle to reduce night-time light exposure. No studies evaluated effects of less nocturnal light exposure on delirium as single interventions.
Improving natural daylight exposure . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint Three observational studies 30,32,73 and one before-after study 47 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 delirium 30,32,73 . Zaal et al. 47 demonstrated reduction in delirium duration, comparing patients in private rooms with more natural light versus less bright multibed rooms; however, there was no difference 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 system 15,49,50 , and five used bright light therapy (BLT) [51][52][53][54][55] . None of the three studies 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 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 receiving circadian lighting and delirium incidence (odds ratio (OR) 1.14; 95% CI 0.55, 2.37; p = 0.73). Pustjens et al. 49 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. 50 measured 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 before reporting final results, but . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) The copyright holder for this preprint this version posted May 28, 2020. . preliminary analysis demonstrated delirium incidence of 38% versus 33% in control versus study patients, with no significant improvement on delirium incidence or duration in the study group.
Four studies investigated use of BLT as a single-component intervention to prevent 51,52,55 or treat 53 delirium, while one study used BLT as an element of a multi-component bundle to manage delirium 54 .
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 lx 51, 52, 55 . Taguchi et al. 51 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 to overall delirium incidence (16% versus 40% study versus control group, p = 0.42).
In another RCT, Ono et al. 52  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. 53 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. 54 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)
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Earplugs and eye mask
One reviewed study explored effects of earplugs and an eye mask on delirium 56 , while two others used earplugs and an eye mask as part of their interventional bundle 7, 58 . All three decreased incidence of delirium, but had different effects on sleep quality. Demoule et al. 56 conducted a RCT on 43 non-sedated ICU patients to investigate impact of sleeping with earplugs and an eye mask from 2200 to 0800 on patient outcomes. They found no improvement in delirium incidence or 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 use of earplugs and eye mask, however those were excluded since none reported results on delirium [74][75][76][77] (Excluded studies; Supplementary Table 3).

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 element 57 or as a part of a sleep promotion bundle 7,58 . Core elements of quiet time were behavioral strategies, minimized bedside activity by clustering care, reduced volume of devices/alarms, and dimmed lights 7,57,58 . The study that implemented daytime quiet time failed to show significant effects on delirium 57 , while two sleep promotion studies decreased delirium incidence using nocturnal quiet time combined with components such as earplugs, eye masks, and pharmacological targets 7,58 . Although the multi-component sleep promotion trials decreased delirium incidence, effectiveness of the separate components is unclear.
McAndrew et al. 57 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 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint Patel et al. 7 studied a nocturnal multidisciplinary environmental sleep promotion program in 338 nondelirious, 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 limits 17 . They additionally reported a significant association between sleep efficiency and 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. 58 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.

Modifiable ICU environmental risk factors for delirium
It is well recognized that ICU environments with round-the-clock activities and a high-tech setting have a negative impact on patients' experience and clinical outcomes due to excessive noise, light, and disturbed sleep and circadian rhythm 13,47,48 .
Noise . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. cognitive function, and lowered comprehension of surroundings associated with high noise levels may contribute to acute confusion and delirium 79,80 . In our review, two of three observational studies investigating association between high noise levels and ICU delirium found no significant effect of high noise levels on delirium incidence 19,20 . 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 was 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 lx 59 . Natural fluctuation of light levels throughout the day contributes to the natural sleep-wake cycle by triggering release and suppression of melatonin. Alteration of the sleep-wake cycle and lack of daylight schedule have been shown to be associated with psychiatric . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint diseases including depression, dementia, and delirium 59 . Day-time light levels in the ICU are below normal daylight levels and above the threshold for sleep disruption at night 59  Abnormal natural light cycles are cited in recent literature as a potential modifiable risk factor for delirium management 59 . 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 summer 29 , while the other found exhaustive evidence ruling out a link between delirium and pre-hospital photoperiod exposure year-round 31 . 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 light 13,46 . 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 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint reports). Recent literature states sleep is disturbed in ICU patients regardless of delirium 19,41 , 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 whether or not they followed 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 with 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.

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 satisfaction 57,81 . 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 (Supplementary   Table 3), 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 management 47,82,83 . Zaal et al. demonstrated a lower delirium duration by modifying ICU design with acoustic considerations, however there was no change in delirium incidence rate 47 . These strategies require major renovation or early construction planning, and further research is required to confirm cost-effectiveness and clinical benefits.
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The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint Staff and family conversations and care-activities are significant sources of ICU noise pollution 16,62,63 . Although behavioral modification might be ineffective as a single-component intervention 64 , lowcost adjustments such as limited bedside conversation, lowered voices, clustered care-activities, minimized TV and overhead use and volume, using vibrating pagers, and visual noise-warning devices may be necessary to achieve better results in sound reduction 7,14,62,63,65,66 , sleep improvement 63 , and decreased delirium 14 . To be successful, continuous awareness, education of staff on the impact of excessive noise exposure, and routine monitoring of implemented strategies is crucial 7 . 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 strategy 65,66 . Use of noise-warning systems has a greater impact on reduction of ambient noise compared with peak noise levels 65,66 . 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 pollution 16,62 , and a large portion are considered false positives 84 . Studies show modifying ICU alarms by lowering volume, optimizing device settings, and filtering false alarms may reduce disturbing alarm noise [85][86][87] . 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 negative consequences of audible alarms 72 . Optimization of alarms was used as an element of a noise reduction bundle and sleep promotion studies of this scoping review 7, 14, 58 .
Abating environmental noise by earplugs or headphones appears feasible and effective to reduce noise and improve sleep in the ICU 48, 56, 67-70 . Here, one study failed to prove benefits of using earplugs and eye masks during sleep on delirium 56 , while another earplug trial decreased risk of confusion, and delayed initiation of cognitive disturbances with no significant effect on incidence of delirium 48 . Given the potential effectiveness and low costs, this method is frequently used in multi-component interventions 7,58 ; however, non-compliancy is a major implementation issue in earplugs studies 56 . A recent metaanalysis 81 reported a 13.1% (95% CI, 7.8-25.4) rate of non-compliancy due to intolerance, anxiety, or . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
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(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint Environmental modification to increase daylight exposure is possible through 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 findings 30,32,73 . 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 severity 51, 53, 55 with sleep promoted in four studies [52][53][54][55] . 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 effect 60 . 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 severity 53 . 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 delirium 59,89 . 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 delirium 15, 49, 50 ; 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-toapply 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 . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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The copyright holder for this preprint this version posted May 28, 2020.  57 . Two neurocritical ICU studies have implemented a two hour quiet time during day and night 93,94 . A significant improvement in subjective sleep and increased staff satisfaction was achieved 93,94 . 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 noise 93 .
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 sleep 58 . It is not clear if improvements in delirium are . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint 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 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.

CONCLUSION
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 study demonstrated overall evidence supporting effectiveness of environmental interventions on delirium is of low confidence. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

(which was not certified by peer review)
The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint recommended to implement these interventions in current practice, especially as multi-component bundles.
. CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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The copyright holder for this preprint this version posted May 28, 2020. .

34.
Bowman AM. Sleep satisfaction, perceived pain and acute confusion in elderly clients undergoing orthopaedic procedures. J Adv Nurs. . CC-BY-NC 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

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The copyright holder for this preprint this version posted May 28, 2020. . https://doi.org/10.1101/2020.05.20.20108373 doi: medRxiv preprint Lifelines, TrackIT screener PP3-S; recording started at noon; PSGs were scored by an EEG technician in 30 second epochs according to the AASM standards; atypical PSGs were re-scored; due to encephalopathy, wakefulness was interpreted using eye-blinking and EEG reactivity Sleep, CBO: 24 hour clinical sleep registration done by attending nurses, noted on a case report form as "asleep" or "awake"; awakenings were registered as transitions from "asleep" to "awake"; measurements included total clinical time awake, total clinical time asleep, and number of hours with logged entries   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.