The effect of working serial night shifts on the cognitive functioning of emergency physicians

Study objective: We sought to determine whether working 5 serial night shifts in the,emergency department results in a decline in physician performance as measured with an intelligence test. Methods: This study compared the cognitive functioning of emergency physicians who worked the day shift (7 AM to 5 Pm) with those who worked 5 consecutive night shifts (11 Pm to 7 AM). The Fluid Scale of the Kaufman Adolescent and Adult - Intelligence Test (KAIT) was administered to 16 emergency medicine residents. Half of the residents (group A) were tested while working day shifts, and the other half (group B) were tested after working 5 consecutive night shifts. After a minimum interval of 2 months, the residents were retested in reverse order, with group A tested after working night shifts and group B tested while working day shifts. Results: A total of 16 emergency medicine residents were tested. A paired t test was used to determine whether day-shift KAIT scores are different from night-shift KAIT scores. The mean day-shift KAIT score was 119.1 (SD=7.7), and the mean night-shift KAIT score was 107.2 (SD=10.2). This difference was significant (mean difference=11.9; 95% confidence interval 7.0 to 16.8; P < .001), with the day-shift scores being statistically higher than the night-shift scores. Conclusion: Working a series of 5 night shifts results in a substantial decline in cognitive performance in physicians working in the ED.