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MJA Volume 185 Number 7 2 October 2006 349
Medical staff working the night shift: can naps help?
R Doug McEvoy and Leon L Lack
Napping at night may benefit both health professionals and their patients
elivering medical care is a 24-hour business that inevita-
bly involves working the night shift. However, night shift
requires the health professional to work when the bodys
clock (circadian system) demands sleep. Added to this is the
problem of “sleep debt”, arising from both prolonged prior
wakefulness on the first night shift and cumulative sleep debt
after several nights’ work and repeated unsatisfactory daytime
sleeps. A further aggravation, particularly for trainee medical staff
in teaching hospitals, has been the demand for excessive work
hours across the working week. As has been dramatically shown
in recent well controlled studies, the net result of this assault on
the sleep of health professionals can be impaired patient safety,
and the health and safety of health professionals themselves.
The good news is that health organisations and regulators are
beginning to treat the matter seriously. In Australia, the United
States and Europe, work hours of medical staff have recently
been shortened by government regulation, and bodies such as
the Australian Medical Association and professional colleges are
advising their members on strategies to improve their sleep
health and thus work safety. A recent publication prepared by the
Royal College of Physicians (London) (RCP), Working t he night
shift: preparation, survival and recovery. A guide for junior doctors, is
an excellent example.
One proposed countermeasure for exces-
sive sleepiness is the use of strategically placed naps both before
and during the night shift. But does napping either before or
during the night shift reduce sleepiness and improve perform-
ance, and, if so, how practical is it?
There are two important, independent mechanisms of sleep
and sleepiness that hold the key to these questions.
Probably the
more potent mechanism impairing night-shift alertness is the
circadian system. For most individuals, even those working
permanent night shift, the circadian system is in sleep mode
during the night. This causes slowed reactions, increased feelings
of fatigue, impaired concentration, and increased sleep propen-
sity. The second important mechanism affecting night-time alert-
ness is homeostatic sleep drive. This increases in intensity the
longer we are awake and, like appetite which is sated by eating,
homeostatic sleep drive is reduced by sleeping. If the first night
shift starts at midnight following a normal wake time at about
8 am, about 16 hours of wake sleep debt has already been
accrued and the rest of the night shift will be performed under
intense homeostatic, in addition to circadian, sleep drive. Per-
formance decrements during this night period can be similar to
those measured in the daytime with a blood alcohol concentra-
tion of 0.05%–0.10%.
Day sleep in the home environment is
likely to be shorter and less effective than night sleep so, even
though second and subsequent night shifts may follow fewer
wakeful hours (8–10 hours), homeostatic sleep drive is likely to
remain elevated during night shifts because of incomplete repay-
ment of the previous sleep debt.
To a limited extent, it is possible to “bank” sleep (or pay off
residual sleep debt) before the first night shift, potentially reducing
subsequent night-time homeostatic sleep drive and improving
alertness and work safety. A long (1–2 hours) nap in the afternoon,
350 MJA Volume 185 Number 7 2 October 2006
as recommended in the RCP report, is best. Afternoon sleep is
more efficient than early evening sleep as it uses the natural
afternoon “dip” in circadian physiology
and avoids the risk of
post-sleep grogginess or sleep inertia impinging on the start of
night duty. Between subsequent night shifts, the aim should be to
maximise daytime sleep length (at least 7 hours) and efficiency by
including the afternoon sleepy period (1–4 pm).
What about napping during a night shift to improve alertness
and reduce errors and accidents? Brief afternoon naps of 10–30
minutes (so-called power naps) improve alertness and perform-
ance. We compared afternoon naps of 5, 10, 20, and 30 minutes
of total sleep.
The 10 minute sleep (about a 15 minute nap
opportunity) produced improvements over the 3 hour post-nap
period in all eight alertness and performance measures, without
any of the post-nap impairment of sleep inertia that followed the
20 and 30 minute naps. Whether these results would be
replicated at, say, 3 am in a night-shift environment, with
considerably greater homeostatic and circadian sleep drive, is
now being tested.
Only a few studies have measured the effects of night-shift
napping. Long naps of about 2 hours appear as effective at about
3 am as at 3 pm.
However, 1–2 hour naps were followed by
sleep inertia, during which alertness was impaired for up to an
Longer naps, although beneficial once sleep inertia has
been dissipated, may be used reluctantly by medical staff wishing
to maintain continuity of patient care.
Briefer naps (18–26
minutes) have also improved performance in night-shift environ-
Therefore, the picture emerging from night-shift nap-
ping studies is similar to that from the afternoon studies. Very
brief naps (10–15 minutes of sleep) may improve alertness
immediately without the negative effects of sleep inertia. How
long this improvement lasts and what is the optimal nap length
on the night shift remains to be determined.
In the meantime, as recommended in the recent RCP guide,
health professionals who work night shift should, for the sake of
their own health and safety and that of their patients, consider
the benefits of night-shift napping. Optimal benefit and a higher
take-up rate are likely for sleep lengths of 10–15 minutes.
Author details
R Doug McEvoy, MD, FRACP, BMedSc, Professor,
Leon L Lack, BA, PhD, Consultant Psychologist,
1 School of Medicine, Flinders University, Adelaide, SA.
2 Adelaide Institute for Sleep Health, Repatriation General Hospital,
Adelaide, SA.
3 School of Psychology, Flinders University, Adelaide, SA.
Correspondence: doug.mcevoy@
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... Besonders betroffen sind Tätigkeiten im Gesundheitswesen, in der Industrie oder im Transportwesen, in welchen die Folgen von Erschöpfung und falschen Entscheidungen weitreichende Konsequenzen haben (Mitler et al., 1988;Philip & Åkerstedt, 2006;McEvoy & Lack, 2006). Besonders drastisch zeigen sich damit einhergehende Probleme am Beispiel einiger Katastrophen, wie den Reaktorunglücken in Tschernobyl und Three Mile Island, dem Öltankerunglück der Exxon-Valdez vor Alaska oder der Chemiekatastrophe von Bhopal, welche sich in der Nacht oder den frühen Morgenstunden ereigneten, wo die niedrige Leistungsfähigkeit der Entscheidungsträger zu dieser Uhrzeit vermutlich zum fatalen Verlauf der Geschehnisse beigetragen hat (Folkard & Tucker, 2003;Mitler et al., 1988). ...
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... Sleep opportunities at work for our trainees were sporadic. Moreover, with interrupted sleep there is sleep inertia with its detrimental impact on performance immediately upon waking 10,11 . Our findings suggest that unless there are designated adequate sleep periods, napping at work should not be relied upon to reduce fatigue. ...
Night shifts expose anaesthesia trainees to the risk of fatigue and, potentially, fatigue-related performance impairment. This study examined the workload, fatigue and coping strategies of anaesthesia trainees during night shifts. A blinded survey-based study was undertaken at a major single centre metropolitan teaching hospital in Australia. All ten anaesthesia trainees who worked night shifts participated. The survey collected data on duration of night shifts, workload, and sleep patterns. Fatigue was assessed using the Karolinska Sleepiness Scale (KSS). There were 93 night shifts generating data out of a potential 165. Trainees tended to sleep an increasing amount before their shift as the nights progressed from 1 to 5. Night 1 was identified as an 'at risk' night due to the amount of time spent awake before arriving at work (32% awake for >8 hours); on all other nights trainees were most likely to have slept 6-8 hours. The KSS demonstrated an increase in sleepiness of 3 to 4 points on the scale from commencement to conclusion of a night shift. The Night 1 conclusion sleepiness was markedly worse than any other night with 42% falling into an 'at-risk' category. The findings demonstrate fatigue and inadequate sleep in anaesthesia trainees during night shifts in a major metropolitan teaching hospital. The data obtained may help administrators prepare safer rosters, and junior staff develop improved strategies to reduce the likelihood of fatigue.
... Most experts agree that napping is the most effective fatigue countermeasure. [28][29][30][31][32][33] A brief nap of 10 min can improve subjective alertness and cognitive performance following a night of restricted sleep. 34 Smith-Coggins et al. demonstrated improved reaction time, alertness, fatigue and i.v. ...
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Physicians worldwide are working round the clock to meet the demands of healthcare systems, especially in acute medical settings such as EDs. Demanding shift work schedules cause fatigue and thus deterioration in mood and motor performance. This article explores the effects of sleep deprivation, focusing on cognition, executive decision-making and the implications for clinical care. Humans are capable of functioning and even adapting to sleep restriction; however, clinicians should be aware of pitfalls and absolute minimums for sleep. Fatigue management training shows promise in enhancing safety in aviation and might have a role in medical shift work. Strategic napping improves performance during night shift in the ED, but does not fully negate fatigue. Drugs offer limited benefit for performance under sleep-deprived conditions, and whenever possible, sleep and/or strategic napping takes precedence.
... For example, Macchi, Boulos and Ranney et al. studied the effects of afternoon nap on nighttime alertness and performance [2]. McEvoy & Lack studied the effects of nap (happens in the night shift) on work efficiency [3]. Mednick, Nakayama and Cantero et al. studied the restorative effects of afternoon naps on perceptual deterioration [4]. ...
30 college students who have the habit of lunch time napping (LTN) participated in experiments under two different conditions: Having lunch time napping and not having lunch time napping. They were asked to complete three tasks in-cluding vigilance reaction, short-term memory, addition arithmetic; their performance was re-corded automatically by computer during 3 dif-ferent periods in the afternoon and early eve-ning. The analysis about the experimental data showed that: as for habitual nappers, midafter-noon nap zone existed, LTN played a very im-portant role in overcoming it, and did great help in enhancing their vigilance in the afternoon and early evening, however, LTN didn't bring sig-nificant positive effect to executing complex tasks (such as short-term memory and addition task) at the periods of time 16:30-17:30, 20:00-21:00. Finally, this article discussed the conclu-sions and its significance.
... [13][14][15][16][17] In order for restorative napping to occur, it has been suggested that managers of health care facilities provide a safe and comfortable resting place for nurses working night shift, ensure that nurses do not miss breaks, and use strategies to combat shift work issues such as fatigue. [18][19][20][21][22] Historically, napping by health care staff during night shift has not been condoned by management, with anecdotal evidence to suggest this still may be the case in some jurisdictions. 23,24 Although critical care nurses may nap on breaks in some facilities during night shift, this phenomenon may not be acknowledged and, moreover, has not been fully explored. ...
Nurses working night shifts are at risk for sleep deprivation, which threatens patient and nurse safety. Little nursing research has addressed napping, an effective strategy to improve performance, reduce fatigue, and increase vigilance. To explore nurses' perceptions, experiences, barriers, and safety issues related to napping/not napping during night shift. A convenience sample of critical care nurses working night shift were interviewed to explore demographics, work schedule and environment, and napping/ not napping experiences, perceptions, and barriers. Transcripts were constantly compared, and categories and themes were identified. Participants were 13 critical care nurses with an average of 17 years' experience. Ten nurses napped regularly; 2 avoided napping because of sleep inertia. The need for and benefits of napping or not during night shift break were linked to patient and nurse safety. Ability to nap was affected by the demands of patient care and safety, staffing needs, and organizational and environmental factors. Nurses identified personal health, safety, and patient care issues supporting the need for a restorative nap during night shift. Barriers to napping exist within the organization/work environment.
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The data of the monitoring of the birth defects of the neural tube for 1985-2007 years from Crimean Republic Medical Genetic Center has been analyzed. The group of comparison: 127 cases of the neural tube defects. The control group: 127 cases of birth of healthy children closest by the time and place of birth (for each case from comparison group). By the method of superposed epochs the weekly values of the hellogeophysical indices (Ap index of geomagnetic activity, Wolf Numbers - index of Solar activity, interplanetary magnetic field polarity) during the gametogenesis and embryo period of prenatal development. The statistical significance of the values of heliogeophysical Indices in the comparison and control groups was calculated using the statistical Wilcoxon criterion for the independent groups. It was founded that during 12-18 days of embryogenesis embryos with neural tube defects the increased geomagnetic activity is probable, comparing with the control group. Since the forming of the major part of the neural tube defects takes place during 2-3 weeks of embryo growth, the increase of geomagnetic activity during or before this stage may be one of the ecological risk factors for this pathology.
Society today works 24 hours a day, forcing organizations and their employees to submit work schedules that go against the natural rhythm of life. Shift work and night work, is an issue that is becoming important, as there are important consequences in physical and mental health of those who work this way. Objective: Analyze the existing scientific evidence of the influence of shift work and night shifts in the onset of burnout syndrome among physicians and nurses. Method: Several databases have been reviewed (Medline, Pubmed, Lilacs, Cochrane), with specific descriptors and bibliography has been obtained according to the criteria of inclusion. Results: 40 articles were located, of which 16 (40%) were studies of nurses and 24 (60%) of physicians, mostly physicians studying their specialty. There seems to be a relationship of the influence of shift work and night shifts with the appearance of burnout syndrome in doctors and nurses. Conclusions: The identification of psychosocial risk factors to which physicians may be exposed will allow us to take preventive measures that can be usefull to improve health and quality of life of this professional group.
To develop a guideline to help guide healthcare professionals participate effectively in the design, construction, and occupancy of a new or renovated intensive care unit. A group of multidisciplinary professionals, designers, and architects with expertise in critical care, under the direction of the American College of Critical Care Medicine, met over several years, reviewed the available literature, and collated their expert opinions on recommendations for the optimal design of an intensive care unit. The design of a new or renovated intensive care unit is frequently a once- or twice-in-a-lifetime occurrence for most critical care professionals. Healthcare architects have experience in this process that most healthcare professionals do not. While there are regulatory documents, such as the Guidelines for the Design and Construction of Health Care Facilities, these represent minimal guidelines. The intent was to develop recommendations for a more optimal approach for a healing environment. Relevant literature was accessed and reviewed, and expert opinion was sought from the committee members and outside experts. Evidence-based architecture is just in its beginning, which made the grading of literature difficult, and so it was not attempted. The previous designs of the winners of the American Institute of Architects, American Association of Critical Care Nurses, and Society of Critical Care Medicine Intensive Care Unit Design Award were used as a reference. Collaboratively and meeting repeatedly, both in person and by teleconference, the task force met to construct these recommendations. Recommendations for the design of intensive care units, expanding on regulatory guidelines and providing the best possible healing environment, and an efficient and cost-effective workplace.
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Napping can enhance alertness during sustained wakefulness, but the importance of the temporal placement of the nap between days and within the circadian cycle remains controversial. To resolve these issues, a between-groups study was conducted with 41 healthy, young adults permitted a 2-h nap at one of five times during a 56-h period otherwise devoid of sleep. Naps were placed 12 h apart, near the circadian peak (P) or trough (T), and were preceded by 6, 18, 30, 42, or 54 h of wakefulness. Visual reaction time (RT) performance, Stanford Sleepiness Scale (SSS) ratings, and sublingual temperature were assessed every few hours throughout the 56 h, which took place in an environment free of time cues. All groups displayed a circadian-modulated decline in RT measures and increases in SSS functions as sleep loss progressed. A nap placed at any time in the protocol improved RT performance, particularly in the lapse domain, but not SSS ratings. Comparisons within groups of circadian temperature cycles for the first versus second day of the protocol indicated that early naps (P6, T18, P30) tended to prevent the mean drop in temperature across days. The earlier naps (P6, T18) yielded more robust and longer lasting RT performance benefits, which extended beyond 24 h after the naps, despite the fact that they were comprised of lighter sleep than later naps. Circadian placement of naps (P vs. T) did not affect the results on any parameter. In terms of temporal placement, therefore, napping prior to a night of sleep loss is more important for meeting subsequent performance demands than is the circadian placement of the nap. SSS ratings suggest that the napper is not aware of these performance benefits. Because the longest lasting RT gains followed early naps, which were composed of less deep sleep than later naps, napping during prolonged sleep loss may serve to prevent sleepiness more readily than it permits recovery from it.
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Reduced opportunity for sleep and reduced sleep quality are frequently related to accidents involving shift-workers. Poor-quality sleep and inadequate recovery leads to increased fatigue, decreased alertness and impaired performance in a variety of cognitive psychomotor tests. However, the risks associated with fatigue are not well quantified. Here we equate the performance impairment caused by fatigue with that due to alcohol intoxication, and show that moderate levels of fatigue produce higher levels of impairment than the proscribed level of alcohol intoxication.
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Following the implementation of the European Working Time Directive Regulations, almost all junior doctors in the UK now work full night-shifts. An RCP 50-member working group was established to develop a practical guide to help junior doctors prepare, survive and recover from working night shifts. The guide, set out in this paper, examines the evidence concerning the hazards of shiftwork, and techniques that can be used to reduce risk. The main advice is to minimise sleep debt by taking additional two-hour sleeps in the afternoon before a shift, and 20- to 45-minute naps during the night shift. It is hoped that the advice will make the challenge of night shift work not only easier to tolerate, but also safer for both hospital patients and their doctors.
Background: Naps during extended work shifts are effective in reducing fatigue in other industries, but the use of a nap as a countermeasure to prevent fatigue in residents is uncertain. Objective: To assess the effects of a call-night nap on resident sleep and fatigue. Design: 1-year, within-participant, paired trial with crossover at midmonth. Setting: Academic teaching hospital. Participants: 38 of 40 internal medicine interns. Measurements: Sleep was measured by using wristwatch actigraphy. By using the experience sampling method on a personal digital assistant, random alerts prompted interns to rate fatigue on the 7-point Stanford Sleepiness Scale (7 is most tired). Hospital paging logs and structured interviews provided information on use of coverage. Intervention: For 2 weeks of every month, interns were assigned to the nap schedule, which provided coverage to on-duty interns from midnight to 7:00 a.m. so that they could finish their work and take a nap. The other 2 weeks of the month constituted a standard schedule. Results: Interns received 41 more minutes of sleep while on call with the nap schedule (185 minutes vs. 144 minutes; P< 0.001). When interns with the nap schedule used coverage, they received 68 more minutes of sleep (210 minutes vs. 142 minutes; P< < 0.001). Despite these small increases in sleep, interns reported less overall fatigue while on the nap schedule than while on the standard schedule (1.74 vs. 2.26; P = 0.017). Postcall fatigue with the nap schedule was lower by nearly 1 point (2.23 vs 3.16; P= 0.036), which is almost equivalent to the difference between on-call and postcall fatigue with the standard schedule (2.06 vs. 3.16). However, use of coverage by interns on the nap schedule was impaired by their desire to care for their patients and concerns about discontinuity of care. Limitations: This was a single-institution study that did not have the power to examine outcomes related to intern or patient well-being. Conclusions: Coverage to allow a nap during an extended duty-hour shift can increase sleep and decrease fatigue for residents.
Two processes play a dominant role in sleep regulation: a sleep-dependent process (Process S) and a sleep-independent circadian process (Process C). The time course of Process S was derived from the spectral analysis of slow wave activity in the human EEG. Its level shows an exponential decline during sleep and an increase during waking. The level of Process S at sleep onset is therefore a function of prior waking time. Process C is reflected by the rhythmic variation of sleep propensity during prolonged sleep deprivation, and is assumed to be controlled by a circadian oscillator. In the model, sleep propensity and the duration of sleep are determined by the combined action of the two processes. The model is able to simulate the variations of sleep duration as a function of sleep onset time. Since the amount of REM sleep is little influenced by prior sleep or waking and shows a marked circadian rhythmicity, it is assumed to reflect largely the level of Process C. The cyclic alternation of nonREM and REM sleep is assumed to result from a reciprocal interaction between the two sleep states. In contrast to previous models, only a single circadian oscillator is required to account for the sleep-wake cycle and the sleep organization under entrained and non-entrained schedules. The model also encompasses sleep regulation in animals and may provide indications as to the phylogenetic origin of sleep.
Evidence from human free-running studies has suggested a close relationship between the timing of the circadian rhythm of core body temperature and the rhythm of sleep propensity. However, this relationship may be questioned by variations of sleep and wakeful activity which could have masked the endogenous temperature rhythm. A constant routine was used here to 'unmask' the endogenous temperature rhythm in addition to frequent sleep trials across a 24-h period to confirm the relationship between temperature and sleep propensity rhythms. Of the 14 healthy, good sleeping subjects 13 had significant 24-h cosine rhythms of sleep propensity. Eight of these also had a significant 12-h cosine rhythm. The eight subjects with both 24-h and 12-h rhythms showed a minor peak of sleep propensity in the early afternoon followed by a though in the early evening (20.00 hours). Sleep propensity then rose rapidly at about midnight to a major peak in the early morning. This was followed by a second trough of sleep propensity in the late morning. The average times of the sleep propensity phases relative to the circadian temperature rhythm were very similar to the earlier free-running studies. Furthermore, the times of the sleep propensity phases were highly correlated with the body temperature minimum. These results suggested the possibility that a common oscillator determines the timing of both the body temperature rhythm and the phases of the sleep propensity rhythm.
This study aimed at examining the effects on the subjective symptoms in nurses of both timing and length of a 2-h nap during a 16-h night shift. Compared to pre-nap levels, sleepiness, fatigue, and dullness increased immediately after napping. Afterwards, sleepiness decreased significantly, and the other symptoms returned to the pre-nap values. The nurses' subjective symptoms after napping were not associated with the timing of the nap and post-nap fatigue lasted longer as the nap time increased (> 1.5 h). These results suggest that for effective napping during long night shifts, the nap length should be determined carefully to avoid persistent sleep inertia.
The purpose of this workplace evaluation was to assess the effects on performance, alertness and subsequent sleep of strategic napping on 12-h overnight shifts. In a counterbalanced crossover design, 24 male aircraft maintenance engineers working in a forward rotating 12-h shift pattern volunteered to take part in the study for two work weeks. During the experimental week, each subject was given the opportunity to take a 20-min nap at work between 01:00 and 03:00 h on each of their two overnight shifts. On the control week no naps were taken on the night shifts. A computerized neurobehavioural test battery was employed to assess performance and subjective levels of fatigue at the beginning and end of each night shift, and pre- and postnap. Subjects were also asked to rate how near they had come to falling asleep while driving to and from work. The results revealed that taking a single 20-min nap during the first night shift significantly improved speed of response on a vigilance task measured at the end of the shift compared with the control condition. On the second night shift there was no effect of the nap on performance. Taking a short nap during either night shift had no significant effect on subjective ratings of fatigue, the level of sleepiness reported while driving to and from work, or subsequent sleep duration and sleep quality. Overall the results suggest some promise for a short duration nap taken in the workplace to counteract performance deficits associated with the first night shift.
Although sleep deprivation has been shown to impair neurobehavioral performance, few studies have measured its effects on medical errors. We conducted a prospective, randomized study comparing the rates of serious medical errors made by interns while they were working according to a traditional schedule with extended (24 hours or more) work shifts every other shift (an "every third night" call schedule) and while they were working according to an intervention schedule that eliminated extended work shifts and reduced the number of hours worked per week. Incidents were identified by means of a multidisciplinary, four-pronged approach that included direct, continuous observation. Two physicians who were unaware of the interns' schedule assignments independently rated each incident. During a total of 2203 patient-days involving 634 admissions, interns made 35.9 percent more serious medical errors during the traditional schedule than during the intervention schedule (136.0 vs. 100.1 per 1000 patient-days, P<0.001), including 56.6 percent more nonintercepted serious errors (P<0.001). The total rate of serious errors on the critical care units was 22.0 percent higher during the traditional schedule than during the intervention schedule (193.2 vs. 158.4 per 1000 patient-days, P<0.001). Interns made 20.8 percent more serious medication errors during the traditional schedule than during the intervention schedule (99.7 vs. 82.5 per 1000 patient-days, P=0.03). Interns also made 5.6 times as many serious diagnostic errors during the traditional schedule as during the intervention schedule (18.6 vs. 3.3 per 1000 patient-days, P<0.001). Interns made substantially more serious medical errors when they worked frequent shifts of 24 hours or more than when they worked shorter shifts. Eliminating extended work shifts and reducing the number of hours interns work per week can reduce serious medical errors in the intensive care unit.
Long work hours and work shifts of an extended duration (> or =24 hours) remain a hallmark of medical education in the United States. Yet their effect on health and safety has not been evaluated with the use of validated measures. We conducted a prospective nationwide, Web-based survey in which 2737 residents in their first postgraduate year (interns) completed 17,003 monthly reports that provided detailed information about work hours, work shifts of an extended duration, documented motor vehicle crashes, near-miss incidents, and incidents involving involuntary sleeping. The odds ratios for reporting a motor vehicle crash and for reporting a near-miss incident after an extended work shift, as compared with a shift that was not of extended duration, were 2.3 (95 percent confidence interval, 1.6 to 3.3) and 5.9 (95 percent confidence interval, 5.4 to 6.3), respectively. In a prospective analysis, every extended work shift that was scheduled in a month increased the monthly risk of a motor vehicle crash by 9.1 percent (95 percent confidence interval, 3.4 to 14.7 percent) and increased the monthly risk of a crash during the commute from work by 16.2 percent (95 percent confidence interval, 7.8 to 24.7 percent). In months in which interns worked five or more extended shifts, the risk that they would fall asleep while driving or while stopped in traffic was significantly increased (odds ratios, 2.39 [95 percent confidence interval, 2.31 to 2.46] and 3.69 [95 percent confidence interval, 3.60 to 3.77], respectively). Extended-duration work shifts, which are currently sanctioned by the Accreditation Council for Graduate Medical Education, pose safety hazards for interns. These results have implications for medical residency programs, which routinely schedule physicians to work more than 24 consecutive hours.