Shiftwork - Fundamentals and Assessment Tools for Occupational Ergonomics - page 645

and performance abilities of the worker. There are now several well-controlled studies which document
the pathological sleepiness levels exhibited by many shiftworkers, both at work 35 and on the drive home
after work. 36 Indeed, one could argue that the latter represents the most dangerous activity that most
shiftworkers ever engage in, and one which, in aggregate, represents a major public safety concern invol-
ving significant loss of life. 37 Prophylactic naps have shown to be beneficial in reducing sleepiness in night
workers before starting a run of night duty (a 2-h nap after lunch is recommended), and some experts
favor short naps during the night shift itself, although controls have to be in place for the worker to
recover from the grogginess of sleep inertia, before operating dangerous machinery or monitoring
equipment.
Many shiftworkers assert that if only they could solve their sleep problem, then everything else
would be quite tolerable. However, because of the impact of the circadian system on sleep, disrupted
sleep may be as much a symptom of shiftwork maladjustment as a cause of it. This idea is demonstrated
clearly in a study by Walsh and colleagues 38 who brought actual shiftworkers into a sound-attenuated,
electrically shielded bedroom for their sleep periods, with the subjects commuting to their work from
the laboratory rather than from home. Even in this closely protected environment, there was a highly
significant difference in duration between the day sleep of night workers and the night sleep of day
workers (306 vs. 401 min). In addition, there were reliable differences between the polysomnographic
characteristics of the sleep, with a smaller amount of REM sleep and a greater proportion of slow-
wave sleep for the night workers. Thus, even if it were economically feasible, the complete soundproofing
and lightproofing of all shiftworkers' bedrooms would not eradicate the problem of sleep for
shiftworkers.
Circadian factors are not the only ones having an impact on a shiftworker's sleep, however. Domestic
and social factors (see Section 33.4) are also crucial in determining the patient's sleep quality and dur-
ation. First, the sleep of the shiftworker is not as protected by society's taboos as that of a day worker; for
example, no one would think of phoning a day worker at 2 am, but few would have qualms about
phoning a night worker at 2 pm. Similarly, unless the shiftworker is in a well-adjusted household, his
(and more especially her) sleep is liable to be truncated by the demands of child care, shopping, and
household management. In viewing the sleep of shiftworkers, one must therefore consider both endogen-
ous and exogenous factors that are going to limit sleep time.
Sleep demands may also be as much of an influence on the other two factors in the triad as a product of
their influence. Much domestic disharmony can be attributed to the shiftworker's need for sleep at a time
when households are usually rather noisy, and impaired mood is a classic symptom of partial sleep loss. 39
Prescribed circadian rhythm coping strategies may not work because the weary shiftworker may be asleep
when he or she would ideally be experiencing bright light and activity.
Finally, in discussing the sleep of shiftworkers, one must address the issue of caffeine to promote alert-
ness, and hypnotics (sleeping pills) to promote sleep. In a study of rotating shiftworkers, Walsh and col-
leagues 40 found that triazolam 0.5 mg could improve the quality and duration of day sleeps. However, the
study was also important in demonstrating that the drug had no significant “phase-resetting” effects.
Thus, on the third- and fourth-day sleeps in a run of night duty, for which no medication was given,
there were no significant differences between those who had been given triazolam on day sleeps 1 and
2 and those who had been given placebo. Moreover, when drug and placebo groups were compared in
terms of nighttime alertness and performance, no reliable differences emerged, even on the days in
which medication was given. 41 One must therefore recognize that hypnotics will probably ameliorate
only the sleep factor of the triad. As a general rule, the use of hypnotics is thus inadvisable for shiftworkers
because problems of tolerance and dependence are likely to occur. It is noteworthy that most hypnotics
are intended only for “occasional transitory insomnia,” and are thus not intended to be taken daily for
months or years at a stretch. The recently available short-acting hypnotics such as zaleplon are unlikely to
be helpful to the shiftworker who is usually suffering from a problem of remaining asleep, rather than
falling asleep. One situation in which hypnotics might be sometimes appropriate is in rapidly rotating
shift systems, in which the occasional day sleep may be improved by hypnotics, and no phase resetting
is required.