Effects of rotating night shifts: literature review

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1 INTEGRATIVE LITERATURE REVIEWS AND META-ANALYSES Effects of rotating night shifts: literature review Sandy Muecke BN GradDipNurs RN PhD Student, Department of Critical Care Medical, Flinders University, Adelaide, South Australia, Australia Accepted for publication 17 September 2004 Correspondence: Sandy Muecke, Department of Critical Care Medicine, Level 3, Flinders Medical Centre, Flinders Drive, Bedford Park, South Australia 5042 Australia. MUECKE S. (2005) Journal of Advanced Nursing 50(4), Effects of rotating night shifts: literature review Aim. This paper reports a review examining the concept of sleep and its antithesis of fatigue, and considers the evidence on nurses ability to cope with the demands of continually changing hours of work, their safety, and the impact any manifestations of sleep disruption may have on the care of their patients. While many aspects of this paper may apply to nursing in general, special consideration is given to nurses in the critical care environment. Background. Night duty rotations are common practice in nursing, and particularly in specialist units. It is essential that nurses working in these environments are able to maintain careful and astute observation of their vulnerable patients, and concern arises when they may be unable to do so. Research suggests that fatigue can negatively affect nurses health, quality of performance, safety and thus patient care, and that the effects of fatigue may be exacerbated for nurses over 40 years of age. Method. The literature was examined for the 10-year period up to December The databases searched were Ovid, Proquest, Blackwell Science, EBSCO Online, Australian Health Review and WebSPIRS, using the keywords of, shiftwork, rosters, intensive care, fatigue, sleep deprivation and sleep studies. Findings. There is consensus amongst researchers on the adverse psychological and physiological effects of night rotations on nurses when compared with their permanent night duty peers, particularly for those over 40 years of age. Evidence also suggests that the effects of fatigue on nurse performance may negatively affect the quality of patient care. Conclusions. The literature reinforces concerns about the adverse relationship between fatigue and performance in the workplace. Optimal standards for patient care may be difficult to achieve for more mature nurses, who may suffer from sleep deprivation and health problems associated with rotational night work and disrupted physiological rhythms. Keywords: nursing, shiftwork, fatigue, sleep deprivation, literature review Introduction Night duty rotations are common practice in nursing. This review shows how poor daytime sleeping may affect normal homeostatic body mechanisms and how fatigue can negatively affect nurse health, quality of performance, safety and thus patient care. Insufficient restorative daytime sleep and inadequate recovery time from nightwork, as described in many studies, may lead to sleep deprivation that may affect nurses abilities to provide the high standard of care that nurses aspire to give to their patients. Compelling evidence is found in the literature about the relationship between fatigue and performance in the workplace, both from a nursing perspective and that of other 7-day rostered occupations. Although nursing and occupational health and safety aspects are acknowledged in the literature, there is little focus on the specific characteristics of some nurses that may make them more susceptible to the adverse Ó 2005 Blackwell Publishing Ltd 433

2 S. Muecke health effects of night duty rotations and hence put at risk patient care and safety. Thus far, however, little research has explored issues of competency, quality of performance and emergent patient and nurse safety issues during night duty rotations, particularly within a critical care setting. Indeed, Poissonnet and Veron (2000) concede that little information exists on the effects of shiftwork on health care professionals. After investigating the concepts of sleep and its antithesis fatigue, consideration is given to the evidence on nurses abilities to cope with the demands of continually changing hours of work, the safety of these nurses and the impact of these issues on patient care. As the literature demonstrates, disruption of circadian rhythms is exacerbated for those over 40 years of age, and so the bodily responses to fatigue on this group of nurses are the focus of this review. Problems associated with lack of sleep have been classified by Barton (1994) and Reid et al. (1997) into three groups, encompassing disturbance of circadian rhythm, physical and psychological problems because of fatigue, and problems associated with a disruption to family life. This categorization is well supported by the literature (Dingley 1996, Learhart 2000). However, because of the complex nature of sleep deprivation, the review will concentrate on the first two of these manifestations, with emphasis on the circadian cycle and the physiological disharmony resulting from fatigue, although psychological disturbances will be briefly acknowledged. Search methods The English language literature was reviewed in early 2002 and late 2003 for papers published from 1992 onwards. The databases searched were Ovid, Proquest, Blackwell Science, EBSCO Online, Australian Health Review and WebSPIRS. The keywords used were shiftwork, rosters, intensive care, fatigue, sleep deprivation and sleep studies. Papers were selected based on their content, relevancy, author, and research validity or rigour. Papers published within the past 10 years were sought, and some were found by searching for specific authors considered by peers to be experts within this domain of knowledge. Other papers were identified from citations and reference lists of already accessed professional literature. Results Sleep In an excellent and comprehensive review of sleep wake cycles citing experiments and theories that evolved from the turn of the 20th century, Lavie (2001) describes the physiological processes of sleep as accepted today. It was not until the 1970s that scientists first noted that sleep propensity seemed to occur in a cyclic fashion that appeared to be controlled by endogenous mechanisms in conjunction with exogenous factors, rather than being solely controlled by environmental factors as previously believed. This cyclical pattern involves a major drive for sleep in the evenings and a lesser drive in the middle of the day. Initially, scientists believed the endogenous cycle had a period of 25 hours, but Lavie (2001) describes recent research showing that this period is almost exactly 24 hours, with only a few minutes deviation. This 24-hour cycle is known as the circadian rhythm, from the Latin circa meaning about and dies meaning day. Many authors (Grossman 1997, Humm 1997, Reid et al. 1997, Fox 1999, Lavie 2001, Turek et al. 2001) state that sleep is controlled by the hypothalamus in the brain. Within the hypothalamus lies the suprachiasmatic nuclei (SCN) that directly communicate with the retina of the eye through the retinohypothalamic nerve pathway. Significantly, Turek et al. (2001) reveal that in 1997 the discovery of the circadian clock gene Clock in mice occurred, linking the gene to SCN diurnal homeostasis in these animals, although the presence of this gene is as yet unproven in humans. The hormone melatonin is very important in relaying environmental information to the brain. Secreted by the pineal gland only during times of environmental darkness, melatonin has receptors located in the SCN and, when injected into the body, it causes drowsiness and inhibits several endocrine functions (Fox 1999, Perkins 2001). Conversely, the cyclical release of the hormone cortisol, a glucocorticoid, helps with day waking. Cortisol, which regulates metabolism and is released in response to stress, is released primarily in the morning and has low levels in the evening (Reid et al. 1997, Perkins 2001). Thus, the pattern of day and night is very important in regulating the circadian clock and sleep wake mechanisms, as normal sleep wake patterns rely on the recognition of day and night by the retina. In a comprehensive synopsis of many studies, Fox (1999) details that during sleep the metabolic rate is lowered, as are the heart rate, respiratory rate and blood pressure as the brain s cortical activity is depressed. Likewise, depressed muscle tone and reflexes also occur. The importance of sleep is further detailed by Fox (1999), who notes that protein synthesis, growth hormone release and cognitive restoration all occur during sleep. Lavie (2001) reviewed the association of normal cyclical temperature changes within the body and circadian rhythms. 434 Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

3 Integrative literature reviews and meta-analyses Normally, people experience a temperature peak in the late afternoon or early evening and a temperature low during the early morning. Experiments reviewed by Lavie (2001) showed a marked correlation between temperature and ability to sleep in that, if sleep commences at about the temperature peak (i.e. in the evening) rather than at the temperature low (i.e. early morning), sleep times almost double. Likewise, performance generally peaks around the time of the evening temperature peak, between 16:00 and 18:00 hours. Therefore, the desire for sleep is at its lowest in the morning as the core temperature begins to rise. Reid et al. (1997) summarize this relationship by stating that: Sleep is of short duration if it starts at the body temperature s low point; sleep is longer if it starts near the peak of the body temperature rhythm, with wake time 2 3 hours after the subsequent minima in core temperature. (p. 442) This is supported by Perkins (2001), who concludes that people who sleep during the day obtain about 4 hours less sleep than night sleepers. Thus, temperature cycles in the body also affect the sleep wake cycle. The circadian-driven propensity for sleep is therefore strongest at night. Night workers must work during the nocturnal release of melatonin and sleep during the day without it, and also against the cortisol-induced desire for morning wakefulness (Perkins 2001, Lamond et al. 2003). Fletcher and Dawson (1997) state that sleep that occurs during times when an individual is biologically driven to be awake tends to be shorter and of decreased quality (p. 474). Many sleep studies have shown that night sleep is the most restful and restorative. Nightworkers are therefore subject to two types of sleep deprivation, as described by Fletcher and Dawson (1997). The first, experienced as a night shift progresses and normal night-time sleep is omitted, is continuous sleep deprivation. The second is cumulative sleep deprivation that occurs over successive days and nights because of shortened sleep times during circadian wake times. Perkins (2001) also discusses this notion of a cumulative sleep debt. Given that day sleeps are often 1 4 hours shorter than night sleeps, night nurses may accumulate a significant number of hours sleep debt even in just 1 week, contributing to long-term exhaustion. Fatigue can therefore be described as a function of the amount of sleep obtained and the time of day when it is received. Although the longer a person works, the more they will tire, it is also vital to relate work to the time of day at which it is performed as, according to Fletcher and Dawson (1997), fatigue accumulates faster during nightwork compared with daywork. Indeed, Fletcher and Dawson (1997, p. 475) contend that no more than two or three night shifts should be worked consecutively in any work block. Fatigue Effects of rotating night shifts The literature links some of the world s worst disasters with fatigue. Rogers et al. (1997) and Harrington (2001) are just some of many authors who attest that the Chernobyl nuclear reactor catastrophe, which occurred at 01:35 hours, was because of human error as a result of nightwork. The environmental disaster of the Exxon Valdez oil spill is also linked to human error and fatigue in many publications, including that of Rogers et al. (1997). Reinforcing these undesirable consequences of sleep deprivation is research by Dawson, an eminent researcher of sleep disorders, and Reid et al. (1997). Their frequently-cited, quantitative experiment compared psychomotor performance of 40 people who were deprived of sleep for 28 hours and then at a later time were asked to consume g of alcohol. Both groups performance deteriorated significantly and, after 17 hours of wakefulness, performance was equivalent to that of a blood alcohol level of 0Æ05% and after 24 hours without sleep, performance was equivalent to that of a blood alcohol level of 0Æ10%. Transferring these findings to nursing practice, would suggest that, if a nurse was to get up at 07:00 hours on the first day of a period of night duty, 24 hours later that nurse would be completing the night shift with performance levels equivalent to those associated with a blood alcohol level of 0Æ10%. Many studies note that staff who work permanent night duty are less likely to suffer sleep-deprivation effects with such acute severity. Dingley (1996) attributed this to the ability of the cycle to adjust itself if given sufficient time. In a comparative study of two groups of nurses, one group working permanent nights and the other rotational nights, Dingley (1996) asked them to assess their levels of alertness using a visual analogue scale and a reaction time test using a computer, over four consecutive nights. Although only a small sample size was used (10 nurses in each group) and the nurses worked in different clinical areas, results clearly showed that alertness improved up to the fourth night as the number of nights progressed, reinforcing the notion of circadian rhythm shifts and adaptation. Not surprisingly, test performance was better at the start of the night shift than at the end, as fatigue progressed. This circadian adaptation is also supported by Lamond et al. (2003), who propose that circadian adjustment is very slow, may take several days or weeks, and may never achieve completion. The Dingley (1996) and Lamond et al. (2003) findings thus undermine the case for rotating night shifts, as Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

4 S. Muecke they highlight the fact that circadian adaptation to nightwork often occurs just in time to return to the day roster. Barton (1994), reviewing several previous studies, noted the fact that permanent night workers choosing rather than being obliged to work at night, in combination with differing personality types, greatly influenced the ability to cope with night duty. This interesting observation could be attributed to the fact that not everyone has the same timing in their circadian clock (Reid et al. 1997, Poissonnet & Veron 2000). Some people appear to have circadian rhythm periods of longer than 24 hours and may have a longer time period between temperature peaks and troughs. Those with such cycles may find that they are more able to cope with nightwork, because of a natural preference for either mornings or evenings (Reid et al. 1997, Learhart 2000). A morning person gets up early, has an active morning and an early night. The night owl sleeps later, is more active in the evening, cannot get to sleep at night and may be more suited to nightwork. When sleep is deprived, the natural circadian rhythm is disrupted and sleep is craved. Perkins (2001) describes the phenomena of micro-sleep, because of continuous or cumulative sleep deprivation when a person may uncontrollably experience altered states of consciousness for periods up to 30 seconds. During this time, there is loss of concentration and no response to environmental stimuli, and this can happen during any activity and becomes more frequent as sleep deprivation continues. Effects of fatigue on health Physiological effects The literature has conclusively identified a relationship between biological body rhythms and the natural propensity for night-time sleep and day-time wakefulness. The power of the circadian pacemaker is best seen when the sleep wake cycle is disrupted and other rhythms of the body become chaotic (Turek et al. 2001). Many cyclical hormone releases in the body are aligned to the circadian sleep cycle, such as those of melatonin and cortisol. Given that nightwork and in particular rotational night work is disruptive to the circadian drive, inter-dependent rhythms of the body are likely to suffer similar physiological upheaval. Higher rates of sick leave are noted amongst rotational shiftworkers (Panton & Eitzen 1997, Reid et al. 1997). Cardiovascular status and haemodynamic functions influence renal perfusion and urine production, digestive tract function, reproductive hormone release and red and white blood cell production. Immune response, too, is diminished in proportion to the amount of sleep debt accumulated (Perkins 2001). Digestive enzymes are secreted in a cyclical fashion, and the unusual eating and fasting times of nightwork are in disharmony with this cycle. Specifically, some of the health problems experienced by shiftworkers because of disrupted biological synchronism include obesity with associated cardiovascular disease and a sixfold increase in the incidence of gastrointestinal disorders such as peptic ulcers, indigestion, nausea, diarrhoea and constipation (Reid et al. 1997, Learhart 2000, Perkins 2001). The circadian pattern of lowering of blood pressure and heart rate at night may result in a higher incidence of ischaemic heart disease in nightworkers. Harrington (2001) concurs and describes Scandinavian studies that support this observation. These studies suggest that the propensity for cardiovascular pathology amongst shiftworkers is not only related to circadian disruption, but also to stress and a poor diet and exercise regime that may be associated with the social upheaval linked with irregular working hours. A higher risk of miscarriage and premature labour is noted amongst shiftworkers (Reid et al. 1997, Perkins 2001). Commonly, menstrual problems (another biological cycle) are also noted among these workers. Perkins (2001) proposes that nurses who suffer from diabetes, heart disease, and some gastro-intestinal disorders, such as Crohn s, disease should avoid night shifts. Asthmatics may also suffer more on nights as, according to Perkins (2001), respiratory irritation is most likely to occur between 04:00 and 07:00 hours. Ageing and night shifts The ability of the circadian cycle to adjust constantly to the changing sleep patterns that must be endured by the rotational night nurse is diminished with age (Reid et al. 1997, Learhart 2000, Poissonnet & Veron 2000, Reid & Dawson 2001, Lamond et al. 2003). This inability to tolerate shiftwork has also been attributed to the diminished ability of older people to achieve sleep that is uninterrupted and of sufficient length, even under optimal conditions. This is typically seen at around years of age and may be exacerbated by other health problems. Interestingly, it seems that even permanent night staff may have difficulty with nocturnal schedules once they reach 40 or 50 years of age (Learhart 2000). Reilly et al. (1997) suggest that there is a natural tendency for older people to become morning people rather than night-owls which makes night work difficult for mature permanent nightworkers, and may contribute to their resignation from permanent nightwork. Given that older nurses are often the most senior and experienced, this has serious ramifications for efficient hospital management, the general standard of patient care and education of junior nurses. 436 Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

5 Integrative literature reviews and meta-analyses Psychological effects of fatigue Problems because of diurnal disruption are not solely physiological. Psychological imbalance can be experienced also (Reid et al. 1997). Fatigue has been well-documented in the literature. In the Maastricht Cohort Study that began in 1998, questionnaires were distributed to 26,978 employees, of whom 12,161 returned the first of the eight questionnaires. Of these respondents, 61Æ9% returned the eighth and final questionnaire (n ¼ 7482) (Jansen et al. (2003). Forty-five different workforce populations were represented and results showed that fatigue may be an underlying cause of cessation of shiftwork in favour of working during daylight hours. Irritability and strain are also noted in the literature (Lushington et al. 1997, Reid et al. 1997). Lushington et al. (1997) also identified that nurses and their partners found shiftwork to be disruptive to their family and social lives. Poissonnet and Veron (2000) describe studies showing that nurses on rotating schedules experienced less job satisfaction and were more likely to leave, when compared with those working fixed shifts. Effects of fatigue on safety The literature shows that sleep deprivation of 24 hours can result in performance levels associated with those of blood alcohol levels of 0Æ10% (Dawson & Reid 1997). Reid and Dawson (2001) suggest that mature people will reach performance levels equivalent to a blood alcohol level of 0Æ10% in less time than their younger workmates. This may mean that a nurse may drive home from work in an unfit state that is detrimental to both the well-being of the nurse and other road users. Hart et al. (2003) concludes that rotating shift workers, probably because of the diminished performance associated with circadian disruption, are at particular risk of having an accident at work. In particular, Swaen et al. (2003) used the Maastricht Cohort Study data to determine if prolonged fatigue and inadequate recovery were precursors of occupational accidents. They found that, while the likelihood of being injured varied amongst different groups of employees, shiftwork (especially nightwork) was strongly linked to an increase in workplace accidents. Participants who worked nights were three times more likely to be injured in a work related accident than day-time workers. The evidence presented clearly describes working conditions that may be fatal. Indeed, Baker et al. (1997) assert that shiftwork should be viewed and managed as a hazardous place to work (p. 452), while Dawson (1997) declares that there is clear scientific evidence that shiftwork is an identified workplace hazard (p. 412). Effects of fatigue on patient safety Effects of rotating night shifts A summary of the hazards of night work is given by Dingley (1996), p. 1248), based on data gathered from many sleep studies. She states: sleep loss, along with the need to work at the low point of circadian cycle, increases the risk of night nurses being less alert than would ideally be the case. This may impair the efficiency with which they carry out their duties and in an extreme case could possibly endanger the life of a patient. Aspects of performance related to disrupted circadian rhythms and deleterious to patient safety have been described by Reid et al. (1997), and include slowing reaction time; delaying responses; failing to respond at the correct time; giving false responses; and causing slowed thinking and diminished memory (p. 442). The implications of fatigued nurses working in any patient care area are undoubtedly important, but the effects of impaired nurse performance in the critical care environment may be more profound. Indeed, Rogers (2002), in a paper addressing sleep deprivation in an emergency department, suggests that small yet vital changes in a patient s condition or medication order errors may be overlooked by a sleepstarved nurse. Given that Bond and Dax (2000, p. 1914) describe critical care nurses as responsible for diagnosing life-threatening conditions and instituting appropriate treatment in an environment equipped for technically advanced methods of assessing and managing patient problems, the necessity for an alert and focused patient care nurse is obvious. This need for nurse astuteness is further supported by the Confederation of Australian Critical Care Nurses Inc. in their document outlining Competency Standards of Specialist Critical Care Nurses. This organization defines a critically ill patient as one characterized by the presence of actual and/or potential life threatening health problems and that the needs of these patients include the requirement for continuous observation and intervention to prevent complications and restore health (Confederation of Australian Critical Care Nurses Inc. 1996, p. viii). A study by Lee et al. (2003) investigating the mortality rates of babies admitted to a neonatal intensive care unit showed that babies born between 24 and 32 weeks of gestation during the study period were 60% (risk-adjusted) more likely to die if born at night, when compared with those of the same gestational age born during the day. That is, 29 extra deaths per 1000 births of babies of less than 32 weeks gestation might have been averted. Three possible reasons were given. First, infants admitted at night were thought to be sicker than those admitted during the day. Second, expert physician care was Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

6 S. Muecke What is already known about this topic There is an adverse relationship between fatigue and quality of performance. Older nurses, specifically those over 40 years of age, may exhibit inferior performance skills compared with those of younger night workers. Fatigue has been implicated in some of the world s worst disasters. What this paper adds Disrupted body rhythms caused by shiftwork lead to major physiological and psychological effects for nurses that may affect patient safety and the quality of care provided. These effects are greater in those over 40 years of age and may be more profound in a critical care setting. The findings of the review raise important questions for the organization and management of a 24-hour health care service. both the young and not quite so young, are physically able to administer the high standards of care that they are obliged both personally and professionally to give. However, this may not be achievable at all times, given that they may be suffering the effects of sleep deprivation that may intensify as they age. The intimate and indivisible relationships between performance, fatigue, recovery, and age that have been shown in this review to contribute decisively to the quality of care during night shifts, and the possible implications of the evidence presented are disturbing for both patients and nurses, particularly in the critical care environment. Acknowledgements Construction of this paper follows the completion of a Bachelor of Nursing Honours degree at the School of Nursing and Midwifery, Flinders University, Adelaide. Special thanks to Dr Lindy King, Senior Lecturer at Flinders University for sharing her extensive research expertise, and particularly for her assistance with drafts and the research process. more readily available during the day. The third reason related to the inferior levels of alertness and performance of medical and nursing staff during nightshifts, linked to fatigue and circadian dis-synchronism. This study clearly supports the notion that patient safety may be at risk during nightshifts in some instances. Conclusion Despite evidence in the literature describing the vital role sleep plays in health maintenance and homeostasis, the adverse consequences of sleep deprivation on nurses health and patient safety have been poorly explored. Furthermore, there is little on the implications of nurse fatigue in specialized settings such as the critical care unit. The literature has shown that fatigued nurses working rotating night shifts, especially those over 40 years of age, may not function at optimal performance levels during the latter hours of a night shift or over successive night shifts as fatigue accumulates. Thus, there are concerns about the health and safety of nurses and the undesirable manifestations of fatigue on the care and safety of patients, particularly in specialist care settings. As professionals in a caring vocation, nurses strive to give safe and effective nursing interventions 24 hours a day, and to treat and support patients in order to achieve the most favourable outcomes. It is therefore essential that nurses, References Baker A., Roberts T. & Dawson D. (1997) Improving shift work management, iii: changing hours of work. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Barton J. (1994) Choosing to work at night: a moderating influence on individual tolerance to shift work. Journal of Applied Psychology 79(3), Bond E. & Dax J. (2000) Critical care in medical surgical nursing. In Assessment and Management of Clinical Problems (Lewis S., Heitkemper M. & Dirksen S., eds), Mosby, St Louis, USA. Confederation of Australian Critical Care Nurses Inc. (1996) Competency Standards for Specialist Critical Care Nurses. Ink Press International, Subiaco, Australia. Dawson D. (1997) Managing shiftwork: not just the roster. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Dawson D. & Reid K. (1997) Fatigue, alcohol and performance impairment. Nature 388(6639), 235. Dingley J. (1996) A computer-aided comparative study of progressive alertness changes in nurses working two different night duty rotations. Journal of Advanced Nursing 23(6), Fletcher A. & Dawson D. (1997) A predictive model of work-related fatigue based on hours of work. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Fox M. (1999) The importance of sleep. Nursing Standard 13(24), Grossman V. (1997) Defying the circadian rhythm: the emergency nurse and the night shift. Journal of Emergency Nursing 23(6), Harrington J. (2001) Health effects of shift work and extended hours of work. Occupational and Environmental Medicine 58(1), Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

7 Integrative literature reviews and meta-analyses Effects of rotating night shifts Hart C., Ward A., Haney M. & Foltin R. (2003) Zolpidem-related effects on performance and mood during simulated night shift work. Experimental and Clinical Psychopharmacology 11(4), Humm C. (1997) The rhythms of life: chronobiology and nursing. Nursing Standard 11(31), Jansen N., van Amelsvoort L., Kirtensen T., van den Brandt P. & Kant I. (2003) Work schedules and fatigue: a prospective cohort study. Occupational and Environmental Medicine 60(Suppl. 1), i47 i53. Lamond N., Dorrian J., Roach G., McCulloch K., Holmes A., Burgess H., Fletcher A. & Dawson D. (2003) The impact of a week of simulated night work on sleep, circadian phase, and performance. Occupational and Environmental Medicine 60(11), e13. Lavie P. (2001) Sleep wake as a biological rhythm. Annual Review of Psychology 52, Learhart S. (2000) Health effects of internal rotation of shifts. Nursing Standard 14(47), Lee S., Lee D., Andrews W., Baboolal R., Pendray M., Stewart S. & the Canadian Neonatal Network (2003) Higher mortality rates among inborn infants admitted to neonatal intensive care units at night. The Journal of Pediatrics 143(5), Lushington W., Lushington K. & Dawson D. (1997) The perceived social and domestic consequences of shiftwork for female shiftworkers (nurses) and their partners. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Panton D. & Eitzen G. (1997) Dynamic rosters: addressing fatigue and recovery issues in the workforce. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Perkins L. (2001) Is the night shift worth the risk? RN 64(8), 65 66, 68. Poissonnet C. & Veron M. (2000) Health effects of work schedules in healthcare professions. Journal of Clinical Nursing 9(1), Reid K. & Dawson D. (2001) Comparing performance on a simulated 12 hour shift rotation in young and older subjects. Occupational and Environmental Medicine 58(1), Reid K., Roberts T. & Dawson D. (1997) Improving shiftwork management ii: shiftwork and health. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Reilly T., Waterhouse J. & Atkinson G. (1997), Aging, rhythms of physical performance, and adjustment to changes in the sleep activity cycle. Occupational and Environmental Medicine 54(11), Rogers A. (2002) Sleep deprivation and the ED night shift. Journal of Emergency Nursing 28(5), Rogers N., Roberts T. & Dawson D. (1997) Improving shift work management. 1: understanding shiftwork. Journal of Occupational Health and Safety Australia and New Zealand 13(5), Swaen G., van Amelsvoort L., Bultmann U. & Kant I. (2003) Fatigue as a risk factor for being injured in an occupational accident: results from the Maastricht Cohort Study. Occupational and Environmental Medicine 60(Suppl. 1), i88 i92. Turek F., Dugovic C. & Zee P. (2001) Current understanding of the circadian clock and the clinical implications for neurological disorders. Archives of Neurology 58(11), Ó 2005 Blackwell Publishing Ltd, Journal of Advanced Nursing, 50(4),

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