after 4 weeks of a light rotation (averaging 44 hours of rotations/week); after 4 weeks of a heavy rotation (averaging 80 hours of rotations/week); after 4 weeks of a heavy rotation with a 0.05% blood alcohol level; and after 4 weeks of a light rotation with a 0.05% blood alcohol level.
Performance measures included the PVT and a simulated driving task. Findings of the Arnedt et al. (2005) experiment indicate that performance impairment after a heavy-call rotation is comparable to the impairment that is associated with a combined 0.04% to 0.05% blood alcohol level and a light-call rotation. Results of this experiment demonstrate that decrements that are created by extended work shifts are similar to the decrements that are created by elevated blood alcohol levels.
Work hours and sleep loss were shown to impact performance in a Category III evaluation by Rogers et al. (2004). A total of 393 registered nurses logged scheduled hours worked, actual hours worked, time of day worked, overtime, days off, and sleep/wake patterns. Questions concerning errors and near-errors were also included. Analysis showed that work duration, overtime, and number of hours worked per week significantly affected the number of errors. The likelihood of making an error increased with longer work hours, and was three times higher when the nurses worked shifts lasting 12.5 hours or more. Working overtime increased the odds of making at least one error, regardless of the originally scheduled length of the shift. Working more than 40 and more than 50 hours per week significantly increased the risk of making an error.
Similar findings were attained in a subsequent Category III evaluation of 2,737 medical interns (Barger et al., 2006). A Web-based survey was conducted across the U.S. in which interns completed 17,003 confidential monthly reports. These 60-item reports contained information concerning work hours, sleep, and activities during the month, number of days off, and the number of extended-duration work shifts (defined as at least 24 hours of continuous work). These interns were also asked to report whether they had made significant fatigue-related or non-fatigue-related medical errors. Other questions assessed how often they had nodded off or fallen asleep during patient care or educational activities.
Analysis revealed a significant relationship between the number of extended-duration work shifts and the reported rates of fatigue-related noteworthy medical errors. Specifically, the number of reported fatiguerelated medical errors increased as the number of extended-duration shifts per month increased. At least one fatigue-related significant medical error was reported in 3.8% of months with no extended-duration work shifts; and at least one fatigue-related significant medical error was reported in 9.8% of months that had between one and four extended-duration work shifts and in 16% of months that had five or more extended-duration work shifts (Barger et al., 2006). Furthermore, the frequency of attentional failures was strongly associated with the frequency of extended-duration work shifts. Evidence from this study further corroborates the negative impact that extended-duration work shifts may have on performance, as well as increased accidents and injuries (Barger et al., 2006; Ayas et al., 2006).
Working extended hours or overnight shifts also poses the added difficulty of requiring performance from an individual at a time when the body is driven to sleep by the circadian system. Sleep, alertness, and cognitive functioning are determined by the interaction of two processes: the endogenous circadian pacemaker and the homeostatic drive for sleep (Czeisler et al., 2001). The endogenous circadian pacemaker generates the 24-hour circadian rhythm that regulates subjective alertness and sleep propensity as well as core body temperature, cognitive functions, and melatonin secretion, as described above (Czeisler, 2006). It is also highly sensitive to light, which is its primary synchronizer. Misalignment of the circadian rhythm results in disturbed sleep, impaired performance alertness, waking-hour melatonin secretion, and reduced levels of nocturnal secretion of growth
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Risk of Performance Errors Due to Sleep Loss, Circadian Desynchronization, Fatigue, and Work Overload
