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The definition of work for the purposes of the European Working Time Directive includes being resident whilst on-call even though asleep. In August of this year, doctors in training will have their working hours reduced to 58 per week. It is therefore inevitable that shift working will replace the present on-call rotas [1]. Where night work forms a major element of the specialty, shift work has already arrived, and it will be imposed on those specialties where those on duty during the day cover for the night hours. Continuity has been provided traditionally by those in training at the expense of long working hours and excessive fatigue.

The benefit of continuity was to be fewer handovers and less cross-cover, both significant contributors to error [2]. However, both sleep deprivation [3] and shift working [4] are potent contributors to error rates in clinical practice. Consequently, the relentlessly increasing demand for shift work has led to the replacement of disquiet by mounting concern for the health of doctors as well as their productivity and error rates. In an effort to minimise the damaging potential the Association of Anaesthetists of Great Britain and Ireland convened a working party to study the impact of fatigue on anaesthetic practice and a report of their deliberations has recently been published [5].

Despite over half a century of research into the effects of shift work, there remain many unresolved issues. Space in this editorial does not permit detailed coverage of the subject. The interested reader, however, is referred to two reviews, which have achieved almost cult status [6,7]. These reviews were subject to further scrutiny [8], and were later updated and considered in the light of the implications of the Working Time Regulations [9]. Despite the age of these publications, they remain as pertinent today as when they were first written. All four reviews support the premise that, in respect of the effects of shift work on health, there are two main areas of concern: gastrointestinal dysfunction and the effects of chronic sleep deprivation.

Commonly, gastrointestinal dysfunction in shift workers presents in vague, non-specific ways, with bowel movements, vague stomach pains and loss of appetite. These complaints are two to five times more common in those workers required to work either permanent or rotating night shift as opposed to workers required to work day time or shift work not involving night duty [10].

In view of the poor quality of catering facilities at night, staff frequently rely on snacks and deny themselves an adequate source of nutrition. Digestive disorders in shift workers may therefore reflect such matters as irregular mealtimes and poor quality food. For example there may be undue reliance on prepacked meals and caffeinated drinks. Coffee and cigarettes are used in an effort to keep awake and alcohol to promote sleep whenever it is disrupted. In addition to these issues, other factors might come into play, including lack of appetite, unprotected times for meals, being unused to eating during the middle of the night and inadequate opportunities to socialise with friends and colleagues.

There may also be differences in metabolism between day and night. During the day, food intake results in marked insulin release associated with glucose metabolism and fat storage. At night, glucocorticoids are released and growth hormone secreted. In view of the fasting that takes place, these will lead to fat metabolism and glucose conservation. As physiological adjustment is rarely complete, these hormone profiles are not fully reversed, with the result that glucose is less readily metabolised at night. It has been suggested that this is associated with a rise in plasma LDL-cholesterol. It is this presumed mechanism that potentially links with morbidity findings.

The second area of complaint focuses on chronic sleep deprivation, although there is no conclusive evidence that this results in chronic ill health. Relevant mortality and morbidity, especially with respect to the psychoses, remain largely unresolved. Confounding factors include age, smoking habit, weight, etc. Taking all these into consideration, it seems that night workers have a greater incidence of cardiovascular disorders compared to those who work during the day. This is related to the number of years spent doing night work [11–13].

It is widely believed that the generally low incidence of ill-health in shift workers may present a false picture, being possibly due to selection in the group as a whole. Faced with the prospect of prolonged periods of disability and sickness absence, those failing to adjust to shift work are more likely to leave the system. As a result of this process, there may be greater team cohesion on night shift, and it is tempting and probably true to treat this effect as a confounding factor.

What advice can one give to new shift workers? Those who successfully adapt to shift working manage by restructuring their life style, using zeitgebers. These are the personal cues to the appropriate phase of the light-dark cycle and are available for behavioural adjustment to everyone who works shifts. The aim of this process is to attempt to restructure one's day in such a way that the abnormal timing of personal activities becomes irrelevant.

How can this be achieved? There are several available general approaches. Good sleep hygiene is essential. Napping is particularly important and a very useful means of topping up sleep loss [14]. Their effects vary with their intended outcomes, as prophylactic [15], replacement [16] and maintenance [17][18], naps.

On the other hand, the evidence for the use of melatonin is not strong. Some side-effects have been reported, but since the product remains unlicensed, many cases will go unnoticed. Unlike its use to combat the effects of jet-lag, which will, in effect, be brief, acute therapy, it will be used long-term, albeit intermittently, to combat the effects of shift work. Such long-term use has not been investigated.

Weekly rotation of shifts is the commonest pattern in use in the UK at present. It is easy to incorporate into a conventional life style and has therefore become the most socially acceptable. From a physiological perspective, adaptation to night work will never be either complete or totally absent. The result, albeit variable, will be a physiological compromise and the effects unclear and unpredictable.

Adaptation is not possible and should not be attempted when schedules provide for rapid rotation between shifts. This system generally permits one or two days on each shift before rotating to the next one in sequence. The shift worker needs to concentrate on keeping active at work and creating conditions conducive to day-time sleep. These approaches can help minimise performance deficits and sleep loss alike. They can be supplemented by maintaining one's regular routine to avoid risk of disorientation. Naps, particularly in the afternoon, are also useful for dealing with the rigours of this system of rapid rotation. Slow rotation, or permanent night work, permits substantial physiological adaptation if at least 10 consecutive shifts are carried out before rotation to the next shift in sequence. Complete adaptation might be possible if the night worker can develop a work-leisure-sleep cycle and can maintain it in the same manner as a day worker. This requires the organisation and use of sleep periods, meal times and personal zeitgebers, in a completely opposite fashion to the rest of ‘normal’ society. Risks arise, however, on rest days, since physiological adjustment is not only lost, but disappears rapidly. This can be minimised by maintaining some sleep by day and some activity at night, although most workers are likely to find this unacceptable.

When facing an irregular shift schedule, it is always best to maintain a 24-h pattern activity schedule. This usually requires a combined use of personal zeitgebers, meal times and a part of one's sleep at a regular time each day [19].

Giving advice to workers is one aspect of managing the effect of shift work. Some attention can be given to the design of the shift system. Normally, these are designed in response to local needs and rarely is any consideration given to those who will have to work the shift and, in particular, their health. With a little thought and some knowledge, it is relatively easy to manage the impact on health and minimise the effects of shift work on performance. Shifts can be characterised by the number of hours worked per shift, the speed of shift rotation and the direction of rotation of the shifts.

Normally, shifts last for 8 h, but increasingly 12 h is becoming the norm in civilian life, with 6 h on and 12 h off in a military context. Longer shifts are more likely to produce fatigue, loss of sleep and performance decrement. Shorter shifts therefore are often used to reduce fatigue-related error, especially where highly sophisticated equipment might be used. Altering the work undertaken during shift may help to reduce boredom. There is no evidence to support the notion that slow rotation of shifts is better than a more rapid one. A permanent night-shift system or slow rotation is often preferred, as the argument is often made that the principal aim should be the adjustment of circadian rhythm. The rate of rotation should, however, only be slow if there is a reasonable chance that daytime sleep can be taken satisfactorily. If this is at all in doubt, rapid rotation might be more appropriate.

Irregular shifts and those based on non-24-h cycles, such as occur in the military, can lead to disruption of 24-h rhythms and the emergence of one based on 25 h, presumably due to loss of zeitgebers. In the short term, symptoms similar to those of jet lag and shift work become manifest and staff become disoriented. Long-term health effects are unknown.

Slow rotation should be in the phase, delay direction, that is to say, morning-afternoon-night-rest-days. Switching from an advancing schedule to this more appropriate one has been shown to improve well-being and productivity.

The reverse sequence, afternoon-morning-night-rest-days, is often preferred by the work force, as there is an extra day between workdays and the first workday does not begin with an early shift. However, physiological adjustment is harder to achieve by this direction of rotation. Also, whenever there is a shift change, there are only 8 h between the end of one and the start of the next shift, which may be an inadequate length of time to make the shift change effective. This will become more frequent with rapid rotation. Days off should be taken after the night shift, to ensure that any sleep debt can be replaced when it is most needed.

There is little doubt that shift work will affect the health and performance of those who work at night. The Health of Munitions Workers Committee was set up in 1915 to the deal with the production of ammunition on a massive scale. Ninety hours a week was common and a 100-h working week was not unusual [20]. The consequence of the inevitable fatigue was an increased error rate. It was soon noted that if one was to make an error at work, a munitions factory was not the best place to do it. Perhaps the same should be said of hospitals. The committee declared a need for ‘a sympathetic and correct understanding of the physical and mental capacities of each worker and their most satisfactory and economical application’[21]. The Committee became the Industrial Fatigue Research Board, later the Industrial Health Research Board and most recently the Medical Research Council.

Proper consideration must be given to the health management of those required to work shifts either at the start or later on in their careers. Attention also needs to be given to the design of shift rotas, appropriate to the work to be undertaken. This is by no means easy and will require extensive consultation with all interested parties. This should involve a consideration of health aspects and employ an evidence-based approach. Yet again, we have an opportunity to heed Santayana's warning [22], that those who ignore the lessons of history are condemned to relive them. The potential benefits are immense in terms of improved performance, productivity, retention of staff and ensuring the safety of our patients.

References

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