Sleep and Alertness in Medical Interns and Residents: An Observational Study on the Role of Extended Shifts

Abstract

Study objectives: Fatigue from sleep loss is a risk to physician and patient safety, but objective data on physician sleep and alertness on different duty hour schedules is scarce. This study objectively quantified differences in sleep duration and alertness between medical interns working extended overnight shifts and residents not or rarely working extended overnight shifts.

Methods: Sleep-wake activity of 137 interns and 87 PGY-2/3 residents on 2-week Internal Medicine and Oncology rotations was assessed with wrist-actigraphy. Alertness was assessed daily with a brief Psychomotor Vigilance Test (PVT) and the Karolinska Sleepiness Scale.

Results: Interns averaged 6.93 hours (95% confidence interval [CI] 6.84-7.03 hours) sleep per 24 hours across shifts, significantly less than residents not working overnight shifts (7.18 hours, 95% CI 7.06-7.30 hours, p = .007). Interns obtained on average 2.19 hours (95% CI 2.02-2.36 hours) sleep during on-call nights (17.5% obtained no sleep). Alertness was significantly lower on mornings after on-call nights compared to regular shifts (p < .001). Naps between 9 am and 6 pm on the first day post-call were frequent (90.8%) and averaged 2.84 hours (95% CI 2.69-3.00 hours), but interns still slept 1.66 hours less per 24 hours (95% CI 1.56-1.76 hours) compared to regular shift days (p < .001). Sleep inertia significantly affected alertness in the 60 minutes after waking on-call.

Conclusions: Extended overnight shifts increase the likelihood of chronic sleep restriction in interns. Reduced levels of alertness after on-call nights need to be mitigated. A systematic comparison of sleep, alertness, and safety outcomes under current and past duty hour rules is encouraged.

Trial registration: ClinicalTrials.gov NCT00874510.

Keywords: actigraphy; alertness; effects of sleep restriction on cognition and affect.; fatigue; medical education; medical interns; psychomotor vigilance performance; shiftwork; sleep deprivation.

Figure 1

Percent of interns sleeping by time of day and shift type. Interns obtained significantly less sleep during on-call nights but recovered some of the sleep lost during post-call days. Interns retired later prior to days off, but also slept later on days off. Interns retired somewhat earlier on nights prior to and in anticipation of on-call days.

Figure 2

Post call napping in interns. (A) The prevalence of napping in the period 9 am–6 pm on the first day post-call was inversely related to the amount of sleep obtained during the on-call night. (B) Sleep lost during the on-call night was partially recuperated by interns through naps on the first day post call. The more sleep interns lost during the on-call night (9 pm–9 am), the more sleep they obtained during the first day post call (9 am–9 pm). However, compared to a regular shift day (7.11 hours sleep per 24 hours), interns were only able to fully recuperate the sleep lost during on-call nights during post call days if they obtained more than 4 hours sleep during on-call nights. All error bars reflect 95% confidence intervals.

Figure 3

Psychomotor Vigilance Test (PVT) response speed analyses. A 3-minute PVT was performed each morning in the hospital (average time PVT was taken was 07:56 am). Higher response speed values reflect faster reaction times on the PVT and higher levels of alertness. The 3/s starting point of the ordinate was chosen as 97% of the observed response speed values fell above this value. Error bars reflect standard errors (SE). (A) PVT response speed was significantly slower in interns after on-call nights compared to all other shifts (all p < .001). (B) PVT response speed in interns depending on minutes elapsed after waking up and relative to those who did not sleep in the 12 hours prior to PVT administration. Response speed was lowest in those who did not sleep at all. In those who did sleep on-call, response speed was decreased in the first hour after waking up due to sleep inertia. It did not differ significantly during this first hour compared to response speed of interns who did not sleep at all (p > .18). (C) PVT response speed in interns and residents increased strictly monotonic with sleep obtained in the 12 hours prior to PVT administration. It was lowest in those who did not sleep at all (0 hours).