Principles and Practice of Sleep Medicine

ALTHOUGH MORE THAN 16% OF WAGE AND SALARY WORKERS ARE SHIFT WORKERS,1 FEW DATA ARE AVAILABLE ADDRESSING THE PREVALENCE OF SHIFT WORK SLEEP DISORDER (SWSD) AND THE FUNCTIONAL IMPAIRMENT THAT IS UNIQUELY ASSOCIATED WITH ITS 2 PRIMARY SYMPTOMS, INSOMNIAAND EXCESSIVE SLEEPINESS.2 In contrast, there have been a number of laboratory and field studies that have focused on the effects of shiftwork schedules on sleep and alertness. Overall, these studies have shown that individuals engaged in shift work experience disturbed sleep and excessive sleepiness relative to day workers.3-9 These symptoms are likely due to the fact that shift workers’ behavioral sleep-wake schedules are out of phase and often in direct opposition to their endogenous circadian rhythms.9-12 The human circadian timing system is tightly entrained by exposure to environmental light.13,14 Normally, environmental light maintains circadian entrainment to the 24-hour day. Late evening light will phase delay rhythms while morning light will advance them.15,16 However, shifts in endogenous rhythms are difficult to maintain except under laboratory conditions where light exposure is restricted to atypical periods of the day and night.17-20 Even in tightly controlled experiments using bright light to shift circadian rhythms, more than 30% of shift workers are unable to attain large phase shifts.21,22 Difficulty limiting light exposure to appropriate times of day is a major reason why most shift workers, even those on permanent night shifts, do not fully

Shift Work Sleep Disorder: Prevalence and Consequences Beyond that of Symptomatic Day Workers RAPID PUBLICATION

ContextConcern exists about the effect of extended resident work hours; however, no study has evaluated training-related performance impairments against an accepted standard of functional impairment.ObjectivesTo compare post-call performance during a heavy call rotation (every fourth or fifth night) to performance with a blood alcohol concentration of 0.04 to 0.05 g% (per 100 mL of blood) during a light call rotation, and to evaluate the association between self-assessed and actual performance.Design, Setting, and ParticipantsA prospective 2-session within-subject study of 34 pediatric residents (18 women and 16 men; mean age, 28.7 years) in an academic medical center conducted between October 2001 and August 2003, who were tested under 4 conditions: light call, light call with alcohol, heavy call, and heavy call with placebo.InterventionsResidents attended a test session during the final week of a light call rotation (non–post-call) and during the final week of a heavy call rotation (post-call). At each session, they underwent a 60-minute test battery (light and heavy call conditions), ingested either alcohol (light call with alcohol condition) or placebo (heavy call with placebo condition), and repeated the test battery. Performance self-evaluations followed each test.Main Outcome MeasuresSustained attention, vigilance, and simulated driving performance measures; and self-report sleepiness, performance, and effort measures.ResultsParticipants achieved the target blood alcohol concentration. Compared with light call, heavy call reaction times were 7% slower (242.5 vs 225.9 milliseconds, P<.001); commission errors were 40% higher (38.2% vs 27.2%, P<.001); and lane variability (7.0 vs 5.5 ft, P<.001) and speed variability (4.1 vs 2.4 mph, P<.001) on the driving simulator were 27% and 71% greater, respectively. Speed variability was 29% greater in heavy call with placebo than light call with alcohol (4.2 vs 3.2 mph, P = .01), and reaction time, lapses, omission errors, and off-roads were not different. Correlation between self-assessed and actual performance under heavy call was significant for commission errors (r = –0.45, P = .01), lane variability (r = –0.76, P<.001), and speed variability (r = –0.71, P<.001), but not for reaction time.ConclusionsPost-call performance impairment during a heavy call rotation is comparable with impairment associated with a 0.04 to 0.05 g% blood alcohol concentration during a light call rotation, as measured by sustained attention, vigilance, and simulated driving tasks. Residents’ ability to judge this impairment may be limited and task-specific.

/pdf/neurobehavioral-performance-of-residents-after-heavy-night-3k8ik3a73p.pdf

Neurobehavioral performance of residents after heavy night call vs after alcohol ingestion.

Medical residents in hospitals are often required to be on duty for long hours. In 2003 the organization overseeing graduate medical education adopted common program requirements to restrict resident workweeks, including limits to an average of 80 hours over 4 weeks and the longest consecutive period of work to 30 hours in order to protect patients and residents from unsafe conditions resulting from excessive fatigue.Resident Duty Hours provides a timely examination of how those requirements were implemented and their impact on safety, education, and the training institutions. An in-depth review of the evidence on sleep and human performance indicated a need to increase opportunities for sleep during residency training to prevent acute and chronic sleep deprivation and minimize the risk of fatigue-related errors. In addition to recommending opportunities for on-duty sleep during long duty periods and breaks for sleep of appropriate lengths between work periods, the committee also recommends enhancements of supervision, appropriate workload, and changes in the work environment to improve conditions for safety and learning.All residents, medical educators, those involved with academic training institutions, specialty societies, professional groups, and consumer/patient safety organizations will find this book useful to advocate for an improved culture of safety.

Resident Duty Hours: Enhancing Sleep, Supervision, and Safety

Impacts of shift work on sleep and circadian rhythms.

http://www.pacdeff.com/pdfs/Dawson_McCulloch%20Managing%20Fatigue%20Its%20About%20Sleep.pdf

Managing fatigue: It's about sleep

Aims: To investigate factors that may contribute to performance adaptation during permanent night work. Methods: Fifteen healthy subjects participated in an adaptation and baseline night sleep, directly followed by seven simulated eight-hour night shifts (2300 to 0700 hours). At the end of each shift they were taken outside and exposed to natural light for 20 minutes. They then slept from approximately 0800 hours until they naturally awoke. Results: There was a significant increase in mean performance on a visual psychomotor vigilance task across the week. Daytime sleep quality and quantity were not negatively affected. Total sleep time (TST) for each of the daytime sleeps was reduced, resulting in an average cumulative sleep debt of 3.53 hours prior to the final night shift. TST for each of the daytime sleep periods did not significantly differ from the baseline night, nor did TST significantly vary across the week. There was a significant decrease in wake time after sleep onset and sleep onset latency across the week; sleep efficiency showed a trend towards greater efficiency across the consecutive daytime sleeps. Hours of wakefulness prior to each simulated night shift significantly varied across the week. The melatonin profile significantly shifted across the week. Conclusions: Results suggest that under optimal conditions, the sleep debt that accumulates during consecutive night shifts is relatively small and does not exacerbate decrements in night-time performance resulting from other factors. When sleep loss is minimised, adaptation of performance during consecutive night shifts can occur in conjunction with circadian adaptation.

https://oem.bmj.com/content/oemed/60/11/e13.full.pdf

The impact of a week of simulated night work on sleep, circadian phase, and performance.

Countermeasures to driver fatigue: a review of public awareness campaigns and legal approaches

This study aimed to provide a comparative index of the performance impairment associated with the fatigue levels frequently experienced in workplaces that require night work. To do this, we equated...

Adaptation of performance during a week of simulated night work

Shift workers encounter an increased risk of cardiovascular disease compared to their day working counterparts. To explore this phenomenon, the effects of one week of simulated night shift on cardiac sympathetic (SNS) and parasympathetic (PNS) activity were assessed. Ten (5m; 5f) healthy subjects aged 18-29 years attended an adaptation and baseline night before commencing one week of night shift (2300-0700 h). Sleep was recorded using a standard polysomnogram and circadian phase was tracked using salivary melatonin data. During sleep, heart rate (HR), cardiac PNS activity (RMSSD) and cardiac SNS activity (pre-ejection period) were recorded. Night shift did not influence seep quality, but reduced sleep duration by a mean of 52 +/- 29 min. One week of night shift evoked a small chronic sleep debt of 5 h 14 +/- 56 min and a cumulative circadian phase delay of 5 h +/- 14 min. Night shift had no significant effect on mean HR, but mean cardiac SNS activity during sleep was consistently higher and mean cardiac PNS activity during sleep declined gradually across the week. These results suggest that shiftwork has direct and unfavourable effects on cardiac autonomic activity and that this might be one mechanism via which shiftwork increases the risk of cardiovascular disease. It is postulated that sleep loss could be one mediator of the association between shiftwork and cardiovascular health.

Kirsty McCulloch

Papers

Managing fatigue: It's about sleep

The impact of a week of simulated night work on sleep, circadian phase, and performance.

Countermeasures to driver fatigue: a review of public awareness campaigns and legal approaches

Adaptation of performance during a week of simulated night work

Daytime cardiac autonomic activity during one week of continuous night shift.