Intensive care units provide specialised care for critically ill patients around the clock. However, intensive care unit patients have disrupted circadian rhythms. Furthermore, disrupted circadian rhythms are associated with worse outcome. As light is the most powerful ‘re-setter’ of circadian rhythm, we measured light intensity on intensive care unit. Light intensity was low compared to daylight during the ‘day’; frequent bright light interruptions occurred over ‘night’. These findings are predicted to disrupt circadian rhythms and impair entrainment to external time. Bright lighting during daytime and black out masks at night might help maintain biological rhythms in critically ill patients and improve clinical outcomes

Blaikley, J

Clark, R

Dark, P

Durrington, HJ

Greer, R

Lucas, RJ

Martial, FP

Ray, DW

Ray, David

Oxford University Research Archive

LETTER TO THE EDITOR Open Access‘In a dark place, we find ourselves’: lightintensity in critical care unitsHannah J. Durrington1*, Richard Clark2, Ruari Greer3, Franck P. Martial4, John Blaikley1, Paul Dark1,5, Robert J. Lucas4and David W. Ray6* Correspondence:Hannah.durrington@manchester.ac.uk1Division of Infection, Immunity andRespiratory Medicine, Faculty ofBiology, Medicine and Health, AVHill Building, University ofManchester, Manchester M139PT,UKFull list of author information isavailable at the end of the articleAbstractIntensive care units provide specialised care for critically ill patients around the clock.However, intensive care unit patients have disrupted circadian rhythms. Furthermore,disrupted circadian rhythms are associated with worse outcome. As light is the mostpowerful ‘re-setter’ of circadian rhythm, we measured light intensity on intensive careunit. Light intensity was low compared to daylight during the ‘day’; frequent brightlight interruptions occurred over ‘night’. These findings are predicted to disruptcircadian rhythms and impair entrainment to external time. Bright lighting duringdaytime and black out masks at night might help maintain biological rhythms incritically ill patients and improve clinical outcomes.BackgroundICU provides specialised care for critically ill patients around the clock; however,patients on ICU have disrupted circadian rhythms [1]. Disrupted circadian rhythms areassociated with impaired survival from critical illness [2].Circadian rhythm disturbances drive impairments in cognition (episodes of delirium)and alter the timing, duration and consolidation of sleep [3].Mechanical ventilation, sedation, severity of illness and the ICU environment (24-hlight and noise) may all cause circadian disruption. It is now clear that light is the mostpowerful environmental influence on the circadian clock, acting through retinal photore-ceptors [4]. Evidence suggests that disruption of a regular 24-h light-dark cycle increasesmorbidity and mortality [2]. It may be possible to ‘reset’ circadian rhythm in critically illpatients using bright light during the day and so improve clinical outcome. The thera-peutic administration of morning bright light has been used for decades in psychiatry totreat seasonal affective disorder. Evidence from neonates suggests that cycled lightimproves sleep, alertness during the day, overall well-being and shortens time untildischarge [5]. A longitudinal study in critical care implemented non-pharmacological en-vironmental changes designed to reduce disturbing patients during the night (noise andlight reduction by use of blackout masks) and demonstrated an impressive reduction indelirium and an improvement in sleep [6]. However, a recent clinical trial of continuousbright light therapy during the daytime in ICU (maximum light intensity 700 lux)concluded that there was no improvement in clinical outcome [7]. Current ICU guide-lines recommend natural daylight for every patient room and artificial light that can beIntensive Care MedicineExperimental© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 InternationalLicense (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, andindicate if changes were made.Durrington et al. Intensive Care Medicine Experimental  (2017) 5:9 DOI 10.1186/s40635-017-0122-9dialled up and down; currently, there is no indication as to what daytime light intensityshould be achieved. The ICU at Central Manchester Foundation Trust opened in 2013and employs windows and artificial, dial up and down, lighting systems. We measuredlight intensity in three different bed locations (a typical bay bed space, a side room with awindow and a side room without a window Fig. 1a) within this newly built ICU, bothduring the day and night.MethodsLight intensity was measured in three different bed locations on ICU (a typical bay bed space,in a side room with a window and in a side room without a window Fig. 1a) over 24–48-hperiods from August to October 2015. A small battery-operated light meter (made in house)was positioned at the patient’s eye level as close to the patient as possible and within 1 m.The light meter recorded ambient light intensity every 15 s. The light sensor of the lightacbd e fFig. 1 Artificial overhead lighting is present throughout the ICU and angle poise lighting is available on a stackat every bedside (a). A typical bed space in an open bay (bed absent). Note the window (i). A typical side-roomwith window (blind is down) (ii). A typical side-room without a window. Note the wall-mounted light box inplace of a window (iii). Mean (±SEM) light intensity across ICU by day and night (b). Mean (±SEM) light intensitymeasured in different locations on ICU during the day and night (c). Fluctuating levels of light intensity are seenin an open bay bed space, which then gradually reduce over the day (d). Typical pattern of artificial lighting ina windowless side-room; a constant day-time light intensity of 180 lux, which abruptly reduces at night-time(e). A side-room with a window demonstrates a combination of natural and artificial lighting during the day (f).A low-intensity night-light has been left on for intervals overnight in (e) and (f). Overnight, there are severalbright ‘pulses’ of light, indicating lights being switched on and off (d), (e) and (f)Durrington et al. Intensive Care Medicine Experimental  (2017) 5:9 Page 2 of 5recorder was optimised for human vision (infrared filtered and peak sensitivity in the greenpart of the spectrum). No change in clinical practice was implemented.Lighting on the ICU is provided by overhead ceiling lights for each bed space (ApolloMulticare, light intensity can be varied 150–500 lux). Overhead lights are switched on at08:00 h and switched off at 23:00 h. Pendant operating lights are used for interventionalprocedures (Trumpf, light intensity up to 160,000 lux). Low-level lighting overnight isprovided by Apollo Lunar.StatisticsLight intensity measurements were analysed as mean ± SEM across time and then bylocation of the light probe. An unpaired t test was used to compare the difference inmeans with significance p < 0.05.ResultsOverall, the mean illuminance across all locations on ICU during the daytime was158.9 ± 0.468 lux (mean ± SEM) and during the night-time was 10.44 ± 0.153 lux (mean± SEM) Fig. 1b. Light intensity was then analysed by location of the probe on ICU.There was significantly increased light intensity during the daytime in the side-roomwith a window (175 ± 0.7614) compared to the open bay bed (166 ± 0.9106) and theside room without a window (138.8 ± 0.5933) Fig. 1c. Over night-time there wassignificantly lower light intensity in the side-room without a window (6.768 ± 0.3589)compared to the open bay bed (12.95 ± 0.2455) and the side-room with a window (11.6± 0.2278) Fig. 1c.Distinct patterns of lighting in different locations on ICU can be recognised. Lightrecordings made in the open bay with window demonstrate gradual increases anddecreases in light intensity at dawn and at dusk Fig. 1d. Light intensity within thewindowless side-room reflects a typical pattern of artificial lighting: a constant ‘block’of daytime light intensity at 180 lux, which abruptly reduces at ‘lights-off ’, around23:00 h Fig. 1e. Overnight, there are several bright ‘pulses’ of light (up to 300 lux),indicating lights being switched on and off as a procedure or check is being carried outFig. 1e and f.DiscussionWe present a description of 24-h profiles of light intensity to which patients in a typicalICU are exposed. Two important features of the ICU environment are apparent in ourdata: significantly low light intensities during the day and frequent overnight lightinterruptions.Starlight on a clear night has an illuminance of ~0.001 lux and moonlight ~0.2 lux .In comparison, sunlight may be as intense as 100,000 lux, and on a heavily overcast,day will still be ∼ 1000 lux. A light intensity of 1000 lux is enough to entrain circadianrhythm [8]. The mean daytime light intensity measured across ICU in this study waslow in comparison to natural daylight at 158.9 ± 0.468 lux (mean ± SEM). This is be-tween 10 and 1000 dimmer than daylight. The consequence for circadian rhythms ishard to predict, but in the absence of scheduled sleep/darkness/activities (as occurs inICU), an imposed 12-h light 12-h dark (dim light) cycle with domestic light at a similarintensity (200 lux) has been reported to be insufficient to maintain circadian phaseDurrington et al. Intensive Care Medicine Experimental  (2017) 5:9 Page 3 of 5position with some individuals drifting to later or earlier times relative to clock time[9]. A recent randomised controlled trial of continuous bright light therapy in ICU [7]failed to find an effect on the incidence of delirium. However, the maximal light inten-sity they achieved for the intervention was 700 lux (substantially below daylight levels)which may not have been a sufficiently large increase to observe an effect.For bright light therapy to be effective in entraining circadian rhythm, it does notneed to be continuous; in fact, exposure to three consecutive bright light ‘pulses’ forjust 15 min can be more effective than continuous bright light [10]. This may also bemore practical for use on ICU. Interestingly, despite the fact that many patients onICU have their eyes closed, it is well recognised that bright light can entrain circadianrhythm through non-visual pathways via the retina [4].Bright light at night can shift the phase of circadian rhythms and reduce their ampli-tude [11]. Such high-intensity light interruptions are necessary for the 24-h care givento critically ill patients; however, wearing a black out mask overnight might minimisethis potential disruption to circadian rhythm.In conclusion, this study has demonstrated significantly low light intensities during the dayon a modern ICU, with frequent overnight light interruptions. With no clear guidelines as towhat daytime light levels should be on ICU, a definitive clinical trial of bright light therapy(>1000 lux) during the day and black out masks at night is required to determine if there is apositive clinical outcome and also if circadian rhythms are re-established.AbbreviationsGAfREC: Governance Arrangements for Research Ethics Committees; ICU: Intensive care unitFundingHD holds an Asthma UK Senior Clinical Academic Development Award. Ref: AUK-SCAD-2013-229.Availability of data and materialsThe datasets generated during the current study are not publicly available but are available from the correspondingauthor on reasonable request.Authors’ contributionsHD conceived the idea for the study, implemented the study design, collected the data, analysed and interpreted thedata and wrote the manuscript. RC and RG collected the data. FM made the light intensity sensor and helpedinterpret the data. RL and DR analysed the data and helped to write the manuscript. PD and JB helped to write themanuscript. All authors read and approved the final manuscript.Competing interestsThe authors declare that they have no competing interests.Consent for publicationNot applicable.Ethics approval and consent to participateConsent—where possible, the purpose of the light recording was explained to patients and relatives. This studyinvolved the use of NHS premises only; therefore, under the Governance Arrangements for Research EthicsCommittees, a REC review was not required. This study received R&D approval from Central Manchester UniversityHospitals NHS Foundation Trust (R03718). The University of Manchester acted as the Research Governance Sponsor.Author details1Division of Infection, Immunity and Respiratory Medicine, Faculty of Biology, Medicine and Health, AV Hill Building,University of Manchester, Manchester M139PT, UK. 2Manchester Emergency and Intensive Care Research Group,Central Manchester Foundation Trust, Oxford Road, Manchester M139WL, UK. 3Intensive Care Unit, Central ManchesterFoundation Trust, Oxford Road, Manchester M139WL, UK. 4Neuroscience and Experimental Psychology, Faculty ofBiology, Medicine and Health, AV Hill Building, University of Manchester, Manchester M139PT, UK. 5Greater ManchesterCentre for Acute Tissue Injury and Trauma, Manchester Academic Health Science Centre, Division of Critical Care,Salford Royal NHS Foundation Trust, Greater Manchester, UK. 6Division of Metabolism and Endocrinology, Faculty ofBiology, Medicine and Health, AV Hill Building, University of Manchester, Manchester M139PT, UK.Durrington et al. Intensive Care Medicine Experimental  (2017) 5:9 Page 4 of 5Received: 20 January 2017 Accepted: 28 January 2017References1. Gazendam JAC, Van Dongen HPA, Grant DA et al (2013) Altered circadian rhythmicity in patients in the ICU. Chest144:483–4892. Carlson D, Chiu W (2008) The absence of circadian cues during recovery from sepsis modifies pituitary-adrenocortical function and impairs survival. Shock 29:127–1323. Fitzgerald JM, Adamis D, Trzepacz PT et al (2013) Delirium: a disturbance of circadian integrity? Med Hypotheses81:568–5764. Lucas RJ, Peirson SN, Berson DM, Brown TM, Cooper HM, Czeisler CA, Figueiro MG, Gamlin PD, Lockley SW,O’Hagan JB, Price LL, Provencio I, Skene DJ, Brainard GC (2014) Measuring and using light in the melanopsin age.Trends Neurosci 37(1):1–9. doi:10.1016/j.tins.2013.10.0045. Morag I, Ohlsson A (2013) Cycled light in the intensive care unit for preterm and low birth weight infants.Cochrane Database Syst Rev Issue 8. Art. 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Lucas RJ, Freedman MS, Muñoz M, Garcia-Fernández J-M, Foster RG (1999) Regulation of the mammalian pinealby non-rod, non-cone, ocular photoreceptors. Science 284:505–50711. Dunlap JC, Loros JJ, DeCoursey PJ (2011) Chronobiology. Sinauer Associates Inc, USASubmit your manuscript to a journal and benefi t from:7 Convenient online submission7 Rigorous peer review7 Immediate publication on acceptance7 Open access: articles freely available online7 High visibility within the fi eld7 Retaining the copyright to your article    Submit your next manuscript at 7 springeropen.comDurrington et al. Intensive Care Medicine Experimental  (2017) 5:9 Page 5 of 5

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‘In a dark place, we find ourselves’: light intensity in critical care units

‘In a dark place, we find ourselves’: light intensity in critical care units

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