"Night-float" systems, which use residents on night shifts to allow physicians working extended work shifts protected time for sleep, have been adopted in many institutions prior to the introduction of ACGME work hour regulations. Night float schedules typically involve a resident being scheduled for night time coverage from a single night to many consecutive nights.  The HWHHSG conducted a study of the impact of sleep and performance when a night float system was used to provide protected time for residents to sleep while on call.  The schedule illustrated below depicts an example of this type of schedule.

Our group used ambulatory EEG recording equipment and a standardized computer-based performance test to monitor sleep and alertness over the course of a 36-hour call day, to examine the extent of sleep deprivation during a typical call night, the workload factors predictive of sleep loss, and the extent to which protected time for sleep within the call night can blunt sleep loss and consequent daytime sleepiness (Richardson 1996). Comparisons were made between interns provided with 4 hours of protected time for sleep by a night float resident and interns without such coverage.  Interns in both conditions spent an average of less than 5 hours attempting to sleep and obtained an average of 3.67 hours of sleep. Provision of the night-float for 4 hours did not significantly change total sleep time.  Sleep efficiency was significantly improved and night float covered interns obtained significantly more slow-wave sleep than the uncovered interns. However, measures of alertness and performance were not significantly different between the two groups. These data suggest that significant chronic sleep deprivation is relatively unaffected by a short sleep obtained in the hospital. 

A potential advantage of a night float system that provides coverage while the day resident sleeps in the hospital at night is that a resident on call can be called upon to deal with patient care when necessary.  Unfortunately this “advantage” is also one of the primary disadvantages of such a system.  In addition, night-float residents often know patients less well than do other team members (particularly if multiple residents share responsibilities as night floats over the course of a week, or if night floats are responsible for an increased number of patients), which may lead to problems due to discontinuity of care, and an increased risk of needing to awaken the sleeping on-call resident.  Frequent awakenings for the resident on call leads to a probable increase in lapses due to sleep inertia.   In addition, residents acting as night floats may themselves be sleep-deprived and error-prone (Cavallo 2003).  If an institution schedules a single person to act as a night float for several consecutive nights, chronic sleep debt builds and shift work sleep disorder may result.  A separate study of the night float system found that increased disturbances of sleep, depressed mood and decreased alertness were present among residents covering the night-float rotation (Cavallo 2002)  Another issue to consider is that in a busy hospital the night float system may lead to the time intended for protected sleep time instead becoming a time when an overworked resident can catch up on charting and other responsibilities.