Evaluation of a rapidly rotating shift system for tolerance of nurses to nightwork.

Fifteen female nurses, aged between 21 and 29 years and employed in an intensive care unit, were examined with the aim of evaluating their psychophysical adaptation to one of the most commonly used, rapidly rotating shift systems, the "metropolitan rota" (2-2-2-2), with the length of the shifts modified according to the work load (including night shifts of 10h) and with the start of the morning shift delayed (to 7 a.m.). Subjective evaluations of work load and psycho-physical conditions as well as performance measures (reaction time, search and memory test), blood pressure and heart rate were recorded at the start, middle and end of the work shifts on the last 4 days of the shift cycle, comprising one morning, one afternoon and two consecutive nights. During the shifts, plasma cortisol and urinary excretion rate of 6-sulphatoxymelatonin, adrenaline and noradrenaline were also recorded, as well as oral temperature and activity-sleep logs. The results showed that this rapidly rotating shift system including two consecutive night shifts does not significantly alter the normal circadian rhythms of the body, particularly as concerns performance levels, body temperature and hormone excretion. Moreover, the lengthening of the night shift to 10h can be considered acceptable in terms of work efficiency, provided that work load is reduced and there are sufficient rest pauses available to compensate for tiredness and sleepiness. On the other hand, the shortening of the day shifts to 7h and the delayed start of the morning shift to 7 a.m. appeared convenient in relation to both work load and sleep duration.