Efficacy of 24-hour shifts: prepared or impaired? A prospective study

The effect of duty duration on performances is unknown. In a prospective cohort study model using repeated measures, we evaluated the effect of shift length on a battery of neuropsychologic performance indicators using our flight program as the test site.

Flight nurses completing 24- and 12-hour shifts were tested on memory, attention, reasoning, motor, and speed measures. Ratings of stress, fatigue, sleep quality, and logged amount of work and sleep were evaluated from personal journals kept for this purpose. Data were analyzed by linear regression and repeated measures multivariate analysis of variance (MANOVA) and analysis of variance (ANOVA). Clinical significance was set at P < 0.05.

Fifteen subjects completed the testing and evaluation process. Neuropsychologic testing demonstrated that performance was not predicted by shift length, time of shift (day versus night), amount or quality of sleep before or during shift, or fatigue ratings. Age, gender, and education did not mediate shift length/test performance relationships. Uninterrupted sleep, stress ratings, and number of flights per shift modestly reduced some test scores. Predictably, repeated testings resulted in practice effects that reduced analysis power. We found that 24-hour shifts per se do not result in a cognitive decline compared with 12-hour shifts. Inconsistent sleep, number of flights, and the stressfulness of flights may have greater impact.