The effect of chronotype on sleepiness, fatigue, and psychomotor vigilance of ICU nurses during the night shift

Abstract

Purpose: In general, sleeping and activity patterns vary between individuals. This attribute, known as chronotype, may affect night shift performance. In the intensive care unit (ICR), night shift performance may impact patient safety. We have investigated the effect of chronotype and social demographics on sleepiness, fatigue, and night shift on the performance of nurses.

Methods: This was a prospective observational cohort study which assessed the performance of 96 ICU night shift nurses during the day and night shifts in a mixed medical-surgical ICU in the Netherlands. We determined chronotype and assessed sleeping behaviour for each nurse prior to starting shift work and before free days. The level of sleepiness and fatigue of nurses during the day and night shifts was determined, as was the effect of these conditions on psychomotor vigilance and mathematical problem-solving.

Results: The majority of ICU nurses had a preference for early activity (morning chronotype). Compared to their counterparts (i.e. evening chronotypes), they were more likely to nap before commencing night shifts and more likely to have young children living at home. Despite increased sleepiness and fatigue during night shifts, no effect on psychomotor vigilance was observed during night shifts. Problem-solving accuracy remained high during night shifts, at the cost of productivity.

Conclusions: Most of the ICU night shift nurses assessed here appeared to have adapted well to night shift work, despite the high percentage of morning chronotypes, possibly due to their 8-h shift duration. Parental responsibilities may, however, influence shift work tolerance.

Fig. 1

The theoretical effect of chronotype on sleepiness. Sleepiness of morning chronotypes (blue) and evening chronotypes (red) is moderated by arousal systems. In this example, on free days (a), the morning chronotype naturally wakes up (sleep offset) at 0700 hours, and the evening chronotype 3 h later. From this point onward, sleepiness steadily increases (dashed line). At some point of low circadian arousal (sleep onset) sleep is enabled to reduce sleepiness. Note the difference in sleepiness between chronotypes at any given time; this is due to the phase difference of the sleep–wake cycle. During night shifts (b), sleepiness keeps increasing despite low arousal. In this example, however, the morning chronotype has a short nap at 2000 hours, which undercuts the projected sleepiness (dashed line) during the night shift. As a result, both chronotypes experience similar sleepiness during the night shift. Afterwards, both chronotypes sleep for approximately 5 h, rapidly decreasing sleepiness, but due to their misalignment with circadian arousal, they both wake up near the peak of circadian arousal

Fig. 2

Sleep times for individual nurses. Sleep onset, offset and mid-sleep times for all 96 participants are displayed for free days (a), sleep before day shifts (b) and sleep before and after night shifts (c). Individual lines represent sleep duration on an average day with the specified shift, starting at sleep onset and ending at sleep offset, dots on lines represent mid-sleep times. Participants are sorted by their MSF^sc (a). The horizontal dotted line separates morning (blue) from evening (red) chronotypes. Note that three participants regularly started day shifts much later than the rest of the cohort