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Medical residents in Canada may work longer hours per shift and per week than their counterparts in Europe, Australia and New Zealand but there is conflicting evidence whether shorter shifts improve patient safety, a new study has found.

In fact, reducing medical resident duty hours may have unforeseen consequences and changes must be made carefully to ensure both patient safety and resident well-being, says University of Toronto medical resident Dr. Reena Pattani, the chief resident at .

Her analysis of resident duty hours was published May 20 in the (CMAJ).

Pattani said residents work an average of 60-90 hours a week in Canada under agreements negotiated between provincial residents’ associations and employers. Residents are limited to 24 to 26 hours of consecutive work, except in Quebec, where on-call shifts were limited to 16 hours after a provincial arbitrator ruled in 2011 that a 24-hour shift posed a danger to residents’ health and violated the Charter of Rights.

In New Zealand, residents are limited to 72 hours of work in a week and 16 hours of continuous work in any one shift. The Australian Medical Association has said that work in excess of 50 hours a week puts the resident at risk. The European Collective Agreement limits residents to 48 hours of work a week.

In the United States, senior residents may work up to 80 hours a week, averaged over four weeks and up to 24 hours continuously, but junior interns are limited to 16 hours of continuous work.

Last year a National Steering Committee on Resident Duty hours said the status quo in Canada was unacceptable and that shifts of 24 hours or longer without sleep should be avoided. It urged all provinces and health care institutions to develop comprehensive strategies to minimize fatigue and fatigue-related risks during residency.

However, concerns that patient care may suffer under the watch of sleep-deprived residents are not borne out by existing evidence, much of which is conflicting over the perceived benefits of shorter hours. Reducing resident hours would also increase workloads of staff physicians and would reduce time for teaching and for learning the practice of medicine. Some studies suggest reduced hours increases the number of errors because it increases the number of shift handovers.

“Although the National Steering Committee challenged the notion of a one-size fits all solution, in doing so it has left out important details, such as how individual residency programs should design fatigue risk management plans,” Pattani and colleagues said in the report. “Will scheduled naps during 24-hour call shifts be sufficient, or will residency programs inexorably move toward shifts that are no longer than 16 hours?”

Pattani (pictured at right; photo courtesy St. Michael's Hospital) said if residents’ work hours are curtailed, it may mean their overall residency periods have to be lengthened so they can see a wide variety and high volume of patients, or teaching hospitals may have to come up with innovative teaching methods, such as greater use of simulation.

Or, they may have to move toward competency-based programs, such as that used by the University of Toronto to train orthopedic surgeons, who can graduate in three or four years, depending on how quickly they attain the necessary skills.

A recent study by Dr. Najma Ahmed, assistant professor at �Թϱ��� and a trauma surgeon at St. Michael’s, also warned about strictly limiting the number of hours surgical residents can work, saying it has not improved patient outcomes but may have increased complications for some patients and led to higher failure rates on certification exams.

Pattani will attend Harvard University next year to study for her Master of Public Health, with a focus on Health and Social Behavior. She received a prestigious Frank Knox Memorial Fellowship for students from some Commonwealth countries.

Leslie Shepherd is a writer with St. Michael's Hospital, a partner of the University of Toronto.