Shift work and quality of sleep: effect of working in designed dynamic light

Prospective intervention study where the effect of the designed dynamic light was examined. ICU staff working in designed dynamic light (intervention group) was compared with staff from a similar ICU with ordinary light (control group).

Primary outcomes were differences in sleep efficiency, level of melatonin, and subjective assessments of sleep quality. Secondary outcome was assessment of work environment.

The main clinical hypotheses were as follows: (1) sleep efficiency and the melatonin level at night would be higher for the intervention group compared to the control group and (2) the intervention group would subjectively assess their sleep as more effective compared to the control group.

In 2011, a Danish ICU was renovated. As part of the renovation, designed dynamic light that changes colour and intensity with time of the day and the work rhythm was installed. The aim was to create lighting conditions as close to daylight variations as possible. The lighting during the day imitated natural daylight, while the light in evening and night changed colour to prevent the suppression of melatonin production. Artificial daylight was made by using warm and cool white fluorescent light tubes with Ra >90, supplemented with tubes of the three primary colours red, green, and blue. Equally spaced 60 × 60 cm ceiling luminaires were Kelvin temperature-controlled using light tubes of the colours 827 and 965, while indirect lighting was provided by 4 × 54 W RGBW up lights, colour 60, 66, 67, and 965 to imitate the reflection of the sun on surroundings in patient rooms and the observation area. All luminaires were glare- and shadow-free with micro prismatic covers. The light changed colour and intensity with time of the day and the work rhythm. Between 5 a.m. and 6 a.m., the light setting gradually shifted from a nightlight to a daylight scenario, which was white in appearance and generally well lit. At 2 p.m., the light intensity decreased slightly to levels just exceeding the light requirements for hospitals (Danish Standard 703 1983). Between 8 p.m. and 10 p.m., a change occurred towards a mix of primarily red, green, and white light. The nightlight between 10 p.m. and 5 a.m. was dim, and the melatonin suppressing blue light was diminished causing the light to appear unnaturally red. In addition, it was in the patient rooms possible to overrule the general electrical lighting by selecting a number of specialised settings: acute, calming, IV catheter, ultra sound, and surveillance, thereby providing safe lighting conditions for all aspects of care. None of the personal computers were modified with diminished blue light during night shifts.

Warm fluorescent light from tubes of the colour 830 placed in equally spaced 60 × 60 cm ceiling luminaires provided the general lighting at the control-ICU with a Ra >85. The ceiling luminaires could be controlled by manual switches in three levels: off, 66 and 100 %. Unlike the corridors, daylight was available during daytime in the observation rooms and patient rooms from windows, but without direct sunlight due to tall buildings close by. The general lighting in the observation rooms was furthermore supplemented by movable desk lamps at each workstation. Movable task lamps and white fluorescent dimmable up lights were used in the patient rooms.

The intervention-ICU was a secondary general ICU with 11 ICU beds, three intermediary care beds, and 14 recovery beds. The ICU received patients from medical and surgical specialities including trauma patients and cardiovascular surgery patients. In the intervention-ICU, the staff had their observation area in a central room with patient rooms all around. The central room was integrated with the corridors connecting to sluice rooms, drug room etc.

The control-ICU was likewise a secondary general ICU with eight ICU beds, one intermediary care bed and 14 recovery beds. Apart from the medical and surgical specialities, this ICU also received patients from the oncology speciality but no trauma patients. In the control-ICU, the staff was divided into two groups with one observation room each located between the patient rooms. The corridor linking the two groups and other rooms was separated from the observation rooms.

Daylight in the intervention-ICU was not present in the clean and unclean sluice room, negligible in the observation work areas, in the work desk areas, and corridors, but slightly present at the patient bedrooms. At the control-ICU, daylight was not present in the clean and unclean sluice room, and negligible in the corridors, but slightly present in the patient bedrooms, the observation rooms and the work desk areas.

At both ICUs, the whereabouts during work hours varied substantially from shift to shift, especially during night shifts, depending on number of patients and their severity of illness. With delirious or severely ill patients, much more time would be spent in the patient rooms for the individual staff member, whereas with stable sleeping or sedated patients, it would be a lot less. Table 1 shows an average estimation of distribution of time spent at different locations in the ICUs.

Nursing staff (registered nurses and nursing assistants) working evening or night shifts, either full time or as part of their work rota, were included. Participants, normally working both evening and night shifts, participated in the project as belonging to either the evening or the night group, depending on which shifts they worked most. All staff who did not work in shifts (supervisors, management etc.), staff not having all of their work during shifts in the ICU (physicians), and staff not working in the designed dynamic light in their shifts were excluded.

All nursing staff eligible for participating in the study received oral and written information about the study and was asked individually if they wanted to participate. Each participant was part of the study for ten consecutive days in which the participant each night slept with a sleep monitor and after each sleep period filled in a sleep diary. Furthermore, each participant provided saliva samples for a melatonin profile on either an evening shift (four samples) or night shift (five samples) and either on a day shift or a day off (two samples). Finally, during the 10-day period, all participants once filled in a general questionnaire about personal characteristics, experiences of quality of sleep both working shifts and not working shifts, and experienced effect of shift work on private life, health issues etc. Additionally, participants from the intervention-ICU filled in a questionnaire about use and experiences of the designed dynamic light.

In both ICUs, the shifts lasted 8 h and 15 min during weekdays and for some of the participants (equal in both ICUs) for 12 h during weekend. Due to the severity of illness of ICU patients, the number of staff at evening and night was close to the number of staff needed during daytime and therefore staff members had a median of 7–8 evening or night shifts a month. In both ICUs, staff overall planned their own work schedule based on individual wishes regarding number of shifts in a row etc., and in both ICUs day shifts began at 7 a.m., evening shifts at 3 pm, and night shifts at 11 p.m. except weekend 12-h shifts which began at 7 a.m. and 7 p.m.

Data collection was conducted from end of February 2013 until mid-May 2013. Participants were enrolled in the project due to availability of sleep monitors (ten available for each ICU) and to when they had a 10-day period with at least two evening or night shifts in a row, 2 dayshifts or 2 days off in a row, and with the possibility to return saliva samples collected at home within 48 h.

When enrolling in the study, each participant received an individual project package containing a sleep monitor (ready for use, coded with the individual’s project code number), a sleep diary with the appropriate dates already entered, information about how to collect saliva samples, a table showing which specific dates to collect saliva samples, and a kit for each saliva sample. All items were marked with the individual’s project code number. The project package was presented by either the project leader or one of the three nursing staff members of the project group. Each part of the project and each item of the package were orally described, using an average of 20 min per participants. The participants also had access to a mobile number they could call at all times if they had any questions during the data collection period. When enrolling in the study, the participants also received an e-mail with a link to the electronic questionnaire (questionnaires for participants from the intervention-ICU). When the participants finished their 10-day data collection period, the sleep monitor and the sleep diary were returned, data from the sleep monitor were downloaded, and the monitor was then coded for the next participant. Data collection quality was monitored throughout the data collection period.

All participants monitored their sleep during the 10-day period using Actisleep Monitors from ActiGraph. The sleep monitors recorded latency (time to sleep onset), number of awakenings, length of awakenings, and an overall sleep efficiency (measured in a percentage, where more than 85 % was considered a normal sleep). The recorded data were analysed using ActiLife software version 6.0. All participants received a copy of their individual sleep monitoring results.

During the sleep monitoring period, the participants filled in a sleep diary daily, recording when they went to sleep, when they got up, how long it took to fall asleep, and what kind of shift (or day off) they had before the sleep period in question. Furthermore, they daily rated the overall quality of their sleep (from level 1 to 5), the level of feeling rested (from level 1 to 5), and the level of feeling awake (from level 1 to 9) of each night’s sleep; each scale had 1 as the best level. They also recorded if they had slept at other times during the day and if there were specific reasons for a disturbed sleep (illness, noise, sick children etc.). The sleep diary was originally developed by the National Research Centre for the Working Environment (NRCWE), Copenhagen, which granted permission for the use in this project. The sleep diary was in Danish, but a non-validated English version is available as supplementary material.

All participants gave saliva samples for melatonin analysis during (1) either an evening or a night shift and (2) either a day shift or a day off. Night shifts samples were collected at 9 p.m., at midnight, at 3 a.m., at 6 a.m. and before the participants went to sleep (or at the latest, 9 a.m.). For evening shifts, samples were collected at 9 pm, at midnight, at 3 am, and when the participants woke up. For day shift or day offs, samples were collected when the participants got up in the morning and just before they went to bed. The saliva samples were collected on the second shift in a row or the second day off and all samples consisted of between 1½ and 2 ml of saliva. The samples were immediately placed in a refrigerator either at the ICU or at home, and within 48 h transferred to the hospital laboratory where it was frozen to minus 80 °C. When data collection was completed, all samples were checked, sorted, and sent for analyses at the laboratory at Gelderse Vallei Hospital, the Netherlands.

During the 10-day period, the participants electronically filled in a general questionnaire with personal characteristics, experiences of quality of sleep both working shifts and not working shifts, and experienced effect of shift work on private life, health issues etc. The questionnaire was originally developed for night shift workers by NRCWE, which granted permission for its use in this project. Two versions were used; one for night shift workers and one adapted for evening shift workers. Additionally, a few questions were added regarding the participants’ general exposure to light and their perception of their work light. The adapted questionnaires were pilot-tested for face and content validity among a small group of nurses and based on their comments and a floor and ceiling effect a few changes were made, among other things an extension of response categories from three (originally: always, sometimes, never) to five (changed version: very often/always, often, sometimes, rarely, never). The updated questionnaires were then again pilot-tested.

Furthermore, the participants from the intervention group filled in a short questionnaire on their experiences of working in the designed dynamic light and how they used the different functions. This questionnaire was developed by The Danish Building Research Institute/Aalborg University, Energy and Environment, Copenhagen (SBi).

The questionnaires were in Danish, but non-validated English versions are available as supplementary material.

Each of the two ICUs was divided into subareas, wherein measuring points in space were selected for doing both horizontal and vertical measurements of photopic illuminance (lux) using a Hagner E4-X Digital Luxmeter, Instr. No. 4111, with corresponding Hagner Detector (B. Hagner AB, Solna, Sweden). The subareas covered the area where the ICU staff worked during shifts and with more than two measuring spots/subareas per room. Comparable subareas and measuring points at the intervention-ICU and control-ICU, respectively, were selected and matched and further used for comparable analysis of the light environments. Comparable subareas at each ICUs included (1) two observation room areas, (2) two patient bedrooms, (3) the clean sluice room, (4) the unclean sluice room, (5) two working desks, and (6) the corridors. Light measurements were performed on a representative day (24 h) on strategically selected time points in accordance with the daily rhythm of light change at the two ICUs.

Horizontal and vertical lux measurements, referring to the orientation of the sensor, were taken 85 cm above the floor at the different selected subareas. Moreover, in the observation rooms, light was measured at the edge of two representative work desks horizontally at 85 cm and vertically at typical eye height of 120 cm above the floor when seated. These measurements can be considered to be a measure of the light on the work desk for office tasks (working light) and the light perceived by a person sitting at a work desk, respectively.

Actiwatch Spectrum™ devices were used to document the diurnal rhythm of the light change being mounted vertically on the walls at a height of 1.5 m and spaced to cover the areas. Further specification about the light measurements can be found as supplementary material.

A pilot study with six participants (three from each ICU) was conducted in 2012, testing sleep monitoring, sleep diary, and collection, transportation and quality of saliva samples.

Twenty sleep monitors were used in the project, and before data collection, all monitors were tested in random intervals between 2 and 10 nights by the study group and their relatives; based on the monitored data, the data analysis software was also tested. Furthermore, all monitors were tested for concordance by being placed on a rotating device for 22 h. The mean registration of rotations was for two different axis, 587.960 (CI 579.386; 596.534) and 591.884 (CI 580.658; 603.111), respectively.

Background characteristics and questionnaire: univariate comparisons between the control and the intervention groups were done by the Mann–Whitney U test, Chi-square test, or Fischer’s exact test where appropriate for a range of key statistics. Data were analysed using Stata version 13 (Juul 2006).

For data from sleep diary (ordered variables), sleep monitoring and melatonin samples, various regression types were used for addressing the questions posed by the clinical hypotheses and analyses were performed using R (R Development Core Team 2014).

The project was approved by The Regional Scientific Ethical Committees for Southern Denmark (S-20110140) and was registered with the Danish Data Protection Agency. Informed consent was obtained from all individual participants included in the study. All procedures performed in the study were in accordance with the ethical standards of the Regional Scientific Ethical Committees and with the 1964 Helsinki declaration and its later amendments.