The purpose of this course is to provide information on fatigue, describe the effects fatigue can have on workers—especially in the healthcare environment—and to suggest ways to lessen or prevent fatigue.
Upon completion of this self-study module, the participant will be able to:
Fatigue may contribute to the human error component of medical errors. Hospitals function around the clock, which necessitates shift work for many personnel. With shortages of some healthcare professionals, some personnel work long hours and are often sleep deprived. Personnel who work during evening hours and at night experience disruptions in circadian rhythms which may aggravate fatigue. Many studies outside the medical field demonstrate the intuitive link between fatigue and degradation in performance. Although both acute and chronic fatigue may have detrimental effects on the health of medical practitioners, the focus of this module is directed at the effects of fatigue and sleep deprivation on patient safety.
One of the most subtle mistakes made is failure to realize that the best-motivated and most highly-trained professionals are also potentially lethal agents. Is working until you drop a badge of honor? Fatigue management in healthcare is a big challenge. Healthcare providers should be made aware that fighting tiredness while trying to provide safe patient care may increase the risk of medical errors. Long before becoming drowsy, fatigue can seriously impair critical thinking ability. This is often referred to as “inattention.” There is a 20 percent decrease in electrical signals after 20 hours of work. However, the actual onset of fatigue occurs somewhere in the spectrum between well-rested and over-worked. At present, some factors in healthcare decrease motivation, and therefore, can bring on fatigue at an early stage. Some of these negative factors include:
Fatigue varies between individuals and may have a synergistic effect with other factors, such as state of mind, motivation, and over-the-counter and prescription medication.
Can you be unsafe to operate a motor vehicle, but still safe to operate on patients? It is doubtful. Research shows 24 hours of wakefulness impairs cognitive performance to the same extent as a blood alcohol level of 0.1 percent, affecting the frontal lobe (memory, attention, concentration, reasoning, sensory recognition, and verbal/nonverbal processes). One study suggested that workers who get two fewer hours sleep than they need are likely to perform at the same level as someone who has had two or three beers. In addition to the serious concerns surrounding the health and safety of the caregivers, caregiver fatigue may also jeopardize patient safety. Although we would never consider allowing colleagues who are alcohol-impaired to set foot on our units, sleep-impaired colleagues are routinely responsible for patients. Healthcare providers who are practicing under the influence of fatigue (PUIF) may not be aware of how tired they are or the seriousness of their impairment. Much like someone who has had too much to drink, sleep-deprived people realize that they are tired but are unaware of the cognitive deficits.
The cognitive processes—how we remember, think, develop and use motor skills to perform activities individually, in teams and within organizational systems—are affected by fatigue.
Fatigue is defined as the state following a period of mental or physical activity characterized by a lessened capacity for work, reduced efficiency, and usually accompanied by feelings of weariness, sleeplessness, or irritability. Fatigue is believed to be related to the degree of sleep deprivation and circadian time of day in a person. Many people simply cannot remain active and productive for an entire workday. This can be devastating to the family breadwinner who cannot hold down a nine-to-five job.
There are two basic types of fatigue: mental and physical. Mental fatigue may occur after some intellectual challenge, such as studying for an exam or giving a speech at work. Physical fatigue may occur after some strenuous physical activity such as mowing the lawn or walking the dog.
Anyone who has ever worked the night shift can quickly conjure up the pervasive sense of fatigue that invades every cell of the body. It is most powerful between the hours of 0300 and 0500. There is a physiological reason for this accelerated sleepiness and the urge to raid the junk food machines in the wee hours of the night. Accelerated sleepiness, associated with staying awake during normative bedtime hours, is primarily driven by a drop in body temperature. This coincides with rapidly rising cortisol concentrations and peak levels of melatonin and thyroid-stimulating hormone. When body temperature reaches its nadir, blood sugar falls. Recovery from maximal sleepiness occurs when the blood sugar stabilizes and body temperature and hormone levels return to pre-sleep deprivation levels.
Sleep deprivation may be described as partial or total, as well as acute or cumulative. The first set of descriptions refers to how much sleep is lost and the second set to the duration of fatigue.
Many individuals believe that they do not need much sleep or that they have adapted to chronic sleep restriction because they do not feel particularly sleepy. This is rarely true. Fatigue is often underestimated, and self-assessments of how sleepy or how alert an individual is are unreliable. The concept of acclimation to sleep deprivation is a myth. Although you can teach yourself to sleep less, you cannot teach yourself to need less sleep. When two to three hours of sleep is missed each 24-hour period, a “Sleep Debt” begins to develop and increases with the accumulation of sleep loss to the extent that one is seldom maximally alert. Missing sleep for one night decreases cognitive performance by 20 to 25 percent. If the sleep debt continues over five to ten days it can result in altered concentration, slowed reaction time, and reduced problem-solving abilities. After 24 hours it is decreased by 70 percent. Reaction time also decreases over consecutive night shifts worked. Although the cognitive deficits associated with sleep deprivation are assumed to be minor or harmless they may have a significant impact on patient safety.
New evidence suggests that sleep deprivation may initiate a chain of events that lead to overeating and obesity. Hyperphagia, or the overwhelming urge to eat, is associated with sleep loss in both rodents and humans. This urge to eat may be related to decreased levels of leptin, an appetite-suppressing hormone secreted by adipocytes. Adequate leptin production is dependent on sleep duration. During sleep deprivation, leptin levels are decreased as much as 20 to 26 percent. Decreased leptin levels signal to the brain that there is a food shortage, prompting an increase in food consumption. The short-term result is increased caloric intake, often well beyond actual caloric needs. The long-term results of high caloric intake, decreased energy and physical activity, and sleep deprivation may contribute to the escalating epidemic of obesity.
The overpowering urge to sleep and the compensatory response--eating to stay awake--are tangible reminders that, although we often take on superhuman tasks and inhumane schedules, we are mere mortals, and as such, our bodies are regulated by a complex series of neurometabolic, hormonal, and circadian rhythms. Although caffeine may help by temporarily enhancing alertness and well-being, it is not the cure, and excessive caffeine use may actually be a large contributor to sleep loss. Caffeine does not treat the root cause (sleep deprivation), and it is also associated with a number of negative health effects.
Shift work usually refers to a schedule in which some employees begin work at times other than the morning. While many of us think of shift work in terms of the midnight-to-eight shift, experts have expanded the definition to include just about any schedule that is outside the nine-to-five routine. That means those people working rotating shifts or having a schedule that involves long, irregular hours are shift workers. In hospitals, up to 35 percent of nurses may be required to work at times other than the day shift. The medical field is just beginning to become aware of the impact of fatigue and shift work on patient safety. Data collected from studies of aviation and space, commercial truck drivers, and the military have demonstrated that the combination of working the night shift and long hours is particularly hazardous. Overall capacity for physical work is reduced at night, short-term memory deteriorates, and on-the-job performance deteriorates.
Ever since the dawn of time, humans have been hardwired to work during the day and sleep at night. Our biology did not change with the invention of the light bulb, even though that made it possible to live and work around the clock. Millions of Americans earn their paychecks by working schedules that are at odds with the body’s biological clock. It is well documented that shift workers have disturbances in their circadian rhythm, as measured by changes in their melatonin and cortisol levels. Because circadian rhythms favor sleeping at night, night shift workers of all types often have difficulties staying awake at night and sleep poorly during the day. Their sleep is shorter, lighter, more fragmented, and less restorative than sleep at night. This leads to cumulative sleep deprivation. Shift workers have poorer quality of sleep, marked by less REM sleep, and are less likely to feel refreshed after awaking. Between 60 and 70 percent of shift workers complain of sleeping difficulties or problem sleepiness. Alertness on the job is also affected, with employees showing less alertness during nighttime shifts. Shift workers tend to perform less well on reasoning and non-stimulating tasks than non-shift workers.
Nurses working the night shift typically average less than four hours sleep per day, with occasional naps, and are awake for periods up to 20 consecutive hours. After nineteen consecutive hours awake, reaction times and other cognitive functions are equivalent to the impairment of that associated with a blood alcohol concentration of 0.1 percent, an amount that is considered unsafe for operating a motor vehicle in many countries. Not only is the first night more hazardous due to the desynchronizing of circadian rhythms, but researchers have shown that the performance of “older” workers, or those of an average age of 40, is more negatively impacted than the performance of younger workers on simulated twelve-hour night shifts.
Circadian rhythms are internally mediated rhythms with frequencies close to 24 hours (e.g. body temperature, sleep/wake cycle). The desire to sleep is the strongest when the body temperature is lowest (e.g. 0300 to 0600), and least likely when the body temperature is at its peak in the late afternoon. Circadian rhythms control virtually every human biological function, including our body’s clock, which determines when we are alert and when we are tired. Basically, humans are programmed for being active in the day and for sleeping at night. The body’s regulation of circadian rhythm is mediated by the effects of light and darkness. Employees who work during dark hours and sleep during daylight hours are often chronically sleep-deprived and may suffer adverse health effects, partially due to poor synchrony of circadian rhythm to work schedules. Scheduled light exposure can produce a phase shift in the endogenous circadian rhythm. The National Aeronautics and Space Administration (NASA) studied the efficacy of bright lights on shuttle astronauts. Their results suggested that alterations in circadian rhythms are obtained by exposure to light at night. The United States Nuclear Regulatory Commission has implemented bright lighting for its night workers and found less fatigue and better alertness on the job. It has not yet been determined how bright artificial light affects objective measures of performance in healthcare workers and medical error. Bright light may not be appropriate for all areas of the hospital, but bright lighting at night may be a relatively inexpensive intervention to decreasing fatigue where possible. Educating workers about the use of heavy shades at home may have an important impact on quality of sleep for night shift workers and may improve job performance on night shift overall.
Fatigue and sleep deprivation are common among medical personnel. Alertness, and ultimately performance, is impacted by the time of day and by the individual caregiver’s alignment of biologic and circadian rhythms; misalignment results in increased fatigue. Multiple studies have documented the impact of fatigue on medical personnel performance. The findings regarding the effects of long work hours on patient safety are straightforward. A recent study established that critical care interns working traditional 24-hour schedules (e.g. 24 hours on and up to 80 hours per week) made 35 percent more errors than those who had schedules limited to shifts less than sixteen hours and who worked less than 60 hours per week. Nurses who work twelve and one-half consecutive hours or more are three times more likely to report making an error than nurses who work fewer hours per day. Working longer than scheduled (overtime), or working 40 hours or more per week, significantly increases the risk of nursing errors.
Although most authorities recommend that adults obtain eight hours of sleep each night (or day for shift workers), recent surveys have shown that most Americans average only 6.8 hours of sleep during the workweek. In a 2005 survey by the National Sleep Foundation, 45 percent of adults report that they sleep less to accomplish more. Individuals differ in their optimal sleep requirements. When adults get less than five hours of sleep over a 24-hour period, peak mental abilities begin to decline. For short periods of time (two to three days) an adult who gets four hours of sleep can function reasonably well, but below peak levels. However, even with sleep deprivation of just a couple of days, slower response times and decreased initiatives are seen. After one night of missed sleep, cognitive performance may decrease 25 percent from baseline. After the second night of missed sleep, cognitive performance can fall to nearly 40 percent of baseline. They are rarely maximally alert, and at some point, general performance, and particularly, cognitive performance, become verifiably worse. Other effects of insufficient sleep include:
Healthcare workers are only human. Humans are by nature fallible and it is unreasonable to expect error-free human performance. Human beings have limited mental and information-processing capabilities, their performance suffers when they are exposed to excessive levels of stress or fatigue, and good intentions are not enough to prevent mistakes from happening. Fatigue and sleepiness affect patient safety in several ways. Physicians and nurses need good vigilance, sound judgment, and quick reaction time, especially in emergency situations. Whether one is evaluating an electrocardiogram or monitoring a patient during general anesthesia, a decrease in attention, memory, or coordination may affect performance and lead to adverse events. Medical errors may be caused by a variety of factors such as calculation errors, lack of knowledge on the part of the nurse or physician, distracting environments, communication breakdowns, and inadequate staffing. In healthcare and other high-risk industries, this human fallibility can have serious and sometimes fatal consequences for patients. Fatigue (from loss of sleep, circadian rhythm changes, and muscular effort expenditure) and long work hours have been identified as contributors to several well-published industrial accidents, such as the explosion at Chernobyl, the Exxon Valdez grounding, Bhopal accident, Three Mile Island nuclear reactor leak and the loss of the Challenger spacecraft. The hazards associated with fatigue and long work hours are often under appreciated by nurses. It is important to understand the signs, prevalence, and impact of sleep deprivation and fatigue.
Healthcare has 24/7 responsibility for continuity of care. How many times have you driven from home to work or work to home and not remembered the last few miles you drove? Some health care providers are especially susceptible to fatigue-related errors:
The 2004 Institute of Medicine (IOM) report, “Keeping Patients Safe – Transforming the Work Environment of Nurses,” advised that the strengthening of patient safety in hospitals, the need for attention to safety defenses, and reinforcing changes in the nursing work environment must involve leadership, the workforce, work processes, and organizational culture changes. IOM recommendations include:
Studies have shown that clinical shifts that extended beyond twelve and one-half hours increased the risk of medical mistakes, such as dispensing the wrong medication or the wrong dosage, at up to three times the normal rate. In non-medical settings, research has shown that shifts that last longer than eight hours lead to more worker fatigue and higher risk of accidents. It has been proposed that work that requires complex cognitive tasks may be ill suited for longer shifts, whereas work with limited cognitive demands may be well suited for longer shifts. Regulation of hours-of-service as an effort to reduce errors due to fatigue is standard in some non-medical fields. Causes for increased errors with long shifts may seem obvious--more overtime equals more physical and emotional exhaustion, less attention to detail and overall burnout.
Any effort to change duty hours for healthcare personnel in an effort to reduce fatigue should factor in and continuously monitor numerous variables, including the potential costs of discontinuity of care, medical complications, and unnecessary hospital days, to ensure that the measures do not compromise patient care. Opponents to changes in work hours argue that restricted working hours will decrease a sense of obligation to patients and will sanction self-interest over the well being of patients. In a perfect world, healthcare professionals would work fewer long shifts and less overtime. But a challenge lies in limiting the time that individuals work at the hospital, especially when most overtime and long shifts are not planned in advance.
The direction of shift rotation may impact worker fatigue. For workers who change from one shift to another, a forward rotation of shift work (morning shifts followed by evening shifts followed by night shifts) may lead to less fatigue on the job than backward rotation (day shift to night shift to evening shift). Forward rotation appears easier to tolerate physiologically since the natural circadian rhythm tends to move forward and it is more difficult to fall asleep earlier than the normal bedtime. Studies have shown that forward rotation allows for better acclimation of the circadian rhythm. However, these studies did not include measurements of error rates with direction of shift rotation.
Another variable in scheduling is the speed of shift-work rotation. Studies suggest that slow rotation (changing from one shift to another every one to two weeks) may allow for better adaptation of the circadian rhythm than fast rotation (e.g. changing shifts every two to three days). Slow shift rotation results in greater sleep length at home, less sleepiness on the job, better self-reported performance, and fewer errors. Shift rotation at an extremely slow rate approximates fixed, non-rotating shifts (permanent night shifts, permanent day shifts). Permanent shifts are associated with better adaptation to changes in the circadian rhythm and better performance than rotating shifts. However, daytime commitments and social obligations often prevent workers form completely adapting to permanent night shifts and worker satisfaction is poor.
The involvement of Joint Commission on Healthcare Accreditation Organization (JCAHO), Agency for Healthcare Research and Quality (AHRQ), Leap-Frog Group, National Quality Forum (NQF), National Patient Safety Foundation (NPSF) and the Institute for Safe Medication Practices (ISMP) in patient safety focus has increased the number of policies and standards of practice to decrease medical errors. Some healthcare providers despise the increase in the number of “rules.” They stress the negative side of policies rather than the goal for increased patient safety. It must be understood that policies and standards of care can benefit them, especially in the event of an adverse patient outcome, and should be supported and followed, not frowned upon.
Because there is no magic bullet for managing sleep deprivation, circadian rhythm disruptions, and fatigue, patient safety advocates recommend a comprehensive program that includes education, alertness strategies, scheduling, and healthy sleep. Health care providers must take personal responsibility for coming to work well rested and encourage colleagues to do the same. The only cure for sleep deprivation is to get more sleep and to do so on a regular basis. On an organizational level, strategies aimed at prevention, recognition, and treatment of fatigue are important. Policies that allow healthcare workers to take sick time or a personal day when sleep problems are unavoidable should be defensible.
Although research says short breaks enhance alertness and concentration, the reality is that less than 50 percent of the time do nurses have a break or meal period free of patient care responsibilities. Even when caregivers are well rested, it is difficult to stay awake for extended periods, particularly on the night shift. It is recommended that units staff for and sanction short naps, scheduled during breaks, on the night shift. To avoid sleep inertia, the naps should be short – between 15 to 40 minutes. Providing fatigued caregivers an alternative mode of transportation home or a place to sleep before the commute may be effective strategies to prevent tragic accidents for those caregivers who have worked an extended shift.
Strong evidence exists to suggest that excessive shift shuffling and doubling back shifts can be harmful to health. Organizations should develop creative staffing models that allow for permanent shift choice and, when possible, minimize excessive rotations. When rotations are necessary, clockwise rotations rather than counterclockwise rotations are easier to synchronize. Mandated rest and recovery days should be provided between off-shift rotations. Exposure to bright light at night may help to reset the nighttime workers’ biological clock and improve mood and energy levels. A fitness program may improve circadian adjustment to non-daytime shifts; it may also help to counteract the risk for obesity and related health problems.
There are no easy answers to the complex issue of what constitutes a safe shift. Some professions already have mandated reductions in continuous work hours. Hospitals should reevaluate both the merits and the perils of extended work shifts, particularly given the impact of fatigue on the aging nursing workforce. At a minimum, strategies are needed to ensure that twelve-hour shifts end on time and to avoid overtime beyond an already extended shift. The use of mandatory overtime is not just controversial, but it is also shortsighted, ultimately a counter-productive pseudo-solution that is potentially dangerous to patients and caregivers alike.
Some healthy suggestions to prevent fatigue from affecting work:
1. Get a good night’s sleep (or day’s sleep for night shift workers). This varies from individual to individual but is somewhere around eight hours per day/night.
2. Schedule regular uninterrupted breaks (about every four hours).
3. Limit caffeine intake. Caffeine is a powerful stimulant, but drinking too much coffee or drinking it late in a shift can interfere with sleep. Also, addiction or tolerance to caffeine leads to its ineffectiveness for fatigue management. Evaluate the amount and timing of caffeine taken on a regular basis. Encourage shift workers to drink coffee at the frond end of the shift and switch to decaf or juice for the rest of the shift.
4. Encourage shift workers to “graze” through their shifts on low-fat, low-sugar snacks such as low-fat crackers, popcorn, pretzels, tossed salads, and veggies with low-calorie dressing/dip.
5. Avoid drugs that may impair work performance.
6. If there is possibility of a sleep disorder, a physician should be consulted. Sleep disorders can result in ineffective or inefficient sleep patterns. This can include sleeping too little or too much. Many of those who suffer from sleep disorders may be able to fall asleep but they nevertheless wake up several times during the night from the slightest noise or disturbance. These people also tend to rise very early in the morning.
7. Improve work culture to support the need for sleep – apply lessons from other industries that minimize shift rotations and excessive work hours. Employ countermeasures such as strategic naps, etc. A 20-minute power nap has been scientifically proven to provide a four-hour boost in alertness and productivity.
8. Exercise, such as a 20-minute aerobic workout, can delay by three to four hours the energy/alertness drop that workers experience during their circadian rhythm low-point and can help workers sleep when their shift is over.
9. Changes to the work environment can reduce physical and mental fatigue. Recent research shows that within certain parameters music is actually a stimulant. Other musts in a work area include bright, full-spectrum lighting, bright colors on the walls, good airflow, and temperature control, as the human brain works best in a 68- to 70-degree environment.
The body’s regulation of circadian rhythm is mediated by the effects of light and darkness. Scheduled light exposure can produce a phase shift in the endogenous circadian rhythm. Manipulation of light and dark is much easier in sleep labs than in the work place, where unintended exposure to bright light is common and may adversely impact attempts to alter workers’ circadian rhythm. The National Aeronautics and Space Administration (NASA) has studied the efficacy of bright lights on shuttle astronauts. Their results suggest that alterations in circadian rhythm can be obtained by exposure to light at night. The United States Nuclear Regulatory Commission has also implemented bright lighting for its night workers and found less fatigue and better alertness on the job. Studies are still needed to determine how bright artificial light affects objective measures of performance in healthcare workers and medical error. Bright light may not be appropriate for all areas of the hospital. Lighting can be a relatively inexpensive intervention using existing equipment. Keeping lights bright at night and educating workers about using heavy shades at home may have an important impact on worker performance on night shift.
Napping is common among shift-workers and is perceived as a way to combat fatigue. The efficacy of naps has been studied in three settings:
There is strong evidence that therapeutic naps and maintenance naps combat the effects of fatigue and sleep loss. They can help subjects adapt better to circadian rhythm disturbances and perform better during acute sleep deprivation. While, prophylactic and therapeutic napping result in loss of social time at home, maintenance napping results in loss of time at work. Napping requires a culture change supported by policy. In most places if you sleep on the job you get fired.
An important consideration in napping is the phenomena of sleep inertia, a period of transitory hypo-vigilance, confusion, disorientation of behavior, and impaired cognitive performance that immediately follows awakening. Sleep inertia is well-documented and lasts up to 30 minutes after awakening. The duration of deep sleep, and the time of the nap relative to the circadian cycle, seems most related to the severity of the sleep inertia. Strategies for napping on the job to reduce fatigue should be designed to avoid possible detrimental effects of sleep inertia. Another potential negative effect of lengthy naps is that they can disrupt the quantity and quality of later sleep periods.
Melatonin is the major hormone responsible for circadian rhythm regulation. Studies on the effect of oral melatonin supplementation on circadian rhythm and adaptation to night shifts have found no effect. Melatonin has been studied for chronic insomnia and other conditions, but there is insufficient evidence to recommend its use to combat fatigue associated with changing work shifts.
Some studies have looked at the potential benefits of benzodiazepines and other sedatives for short-term insomnia associated with shift-work, but there is no data on long-term use. Stimulants and caffeine can boost performance acutely but do not address the underlying sleep deprivation, and thus, are not a viable long-term solution. Concerns over side effects, addiction, and performance degradation with current pharmacologic interventions make their use as a safety practice unlikely.
Sleep deprivation and disturbances of circadian rhythm lead to fatigue, decreased alertness, and poor performance on standardized testing. Although data from non-medical fields suggest that sleep deprivation leads to poor job performance, this link has not been established in medicine. Although the link with fatigue seems intuitive, promoting interventions designed to combat medical errors should be evidence-based. In most high-hazard industries the assumption is that fatigue and long aberrant work hours lead to poor performance and the burden of proof is in the hands of those who believe that such work practices are safe. In healthcare, concerns over discontinuity of care and difficulties in culture change have pushed the burden of proof into the hands of those who wish to change the status quo. Given that healthcare workers, like all human beings, probably function sub-optimally when fatigued, efforts to reduce fatigue and sleepiness should be undertaken and the burden of proof should be placed into the hands of the advocates of the current system to demonstrate that it is safe.
Although twelve-hour shifts are quite popular among both nurses and nurse managers, they may not be appropriate for critical care environments because caring for patients in these units requires a high level of vigilance. Particular attention should be paid to the hours worked by nurses on the night shift, particularly if they are over 40 years of age. Nurses can teach themselves to sleep less, but they cannot teach themselves to need less sleep. Unless severely sleep deprived, healthy adults rarely require over eight hours of sleep per day. Employing good sleep habits, forward rather than backward shift rotation, minimizing shift rotations and excessive work hours, and using strategic naps will reduce the adverse effects associated with fatigue that can put patients, especially the most vulnerable ones, at risk. Fatigue among healthcare workers may not be fully remediable and human errors are, in the end, inevitable. The ultimate solution for health care organizations require a systems based approach that both limits the potential for human error and intercepts errors that do occur before they reach the patient.
Healthcare professionals need to strive to increase awareness and change attitudes so that fatigue and exhaustion are recognized as serious threats to patient safety, rather than a sign of professionalism and dedication. Healthcare providers have a professional responsibility to promote health, happiness, humane working environments, and patient safety.
Buus-Frank, ME. Practicing under the influence of fatigue (PUIF): a wake-up call for patients and providers, Advances in Neonatal Care, Vol. 5, 2005: pp. 55-61.
Dean, Grace E., Scott, Linda D. and Rogers, Ann E., Infants at Risk: When Nurse Fatigue Jeopardizes Quality Care, Advances in Neonatal Care, Vol. 6, No. 3 (June), 2006: pp. 120 - 126.
Gaba, D.M., Howard, S.K., Patient safety: fatigue among clinicians and the safety of patients, New England Journal of Medicine, 2002; 347:1249-1255.
Hughes, R., Stone, P., The perils of shift work: evening shift, night shift and rotating shifts: are they for you? American Journal of Nursing, 2004; 104:60-63
Institute of Medicine of the National Academies. Committee on the work Environment of Nurses and Patient safety. Page A, ed. Keeping patients safe; transforming the work environment of nurses. The National Academy Press, Washington, D.C.: 2004.
National Sleep Foundation. 2005 sleep in America Poll. Washington DC; March 29, 2005. Available at: www.sleepfoundation.org.
National Sleep Foundation. 2003 Sleep in America Poll. Washington DC; March 10, 2003. Available at: www.sleepfoundation.org.
Scott L.D., Rogers, A.E., Hwang, W-T, Zhang, Y., The effects of critical care nurse work hours on vigilance and patients’ safety, American Journal of Critical Care, 2006; 15:30-37.