Sleep strategies of 12-hour shift nurses with emphasis on night sleep episodes.

Objectives: Episodes of sleep during a nightshift are frequently reported in various types of jobs. This phenomenon has been seldom documented so far. This field study investigated individual differences in the sleep-wake behavior of nurses.

Methods: A group of eight nurses working in an intensive care unit on a two 12-hour shift system kept a "sleep diary" for 1 month, recording main sleep periods and naps. They subjectively assessed sleepiness, sleep quality, and the need for sleep at various times of the day and night. Continuous actimetric measurements provided an evaluation of the rest-activity patterns and of the sleep parameters.

Results: Half of the nurses chose to take naps in 75% of their nightshifts. No differences between the night-nappers and nonnight-nappers were found for either total sleep length or the temporal patterns of subjective sleepiness at night but, during nightwork, night-nappers needed sleep earlier than nonnight-nappers. They had long naps during a worknight and short daytime sleep, sometimes followed by a late afternoon nap. This strategy probably favored the maintenance of a diurnal orientation. Nonnight-nappers had long daytime sleep and took preventive naps to anticipate sleepiness during nightwork. However, their readjustment to diurnal life seemed more difficult than that of night-nappers.

Conclusions: Nurses use different sleep-wake strategies to cope with nightwork. These different strategies may be due to circadian influence although social factors cannot be totally excluded.