The study appeared in the Jan. 13 issue of the New England Journal of Medicine.
It is the third in a series of studies on the impact of extended work hours and fatigue on interns conducted by the divisions of sleep medicine at the Brigham and Women's Hospital and the Harvard Medical School in Boston. The three studies were co-funded by NIOSH and the Agency for Healthcare Research and Quality in the U.S. Department of Health and Human Services.
More than 2,700 medical interns participated
For the study, 2,737 first-year doctors -- known as interns -- from institutions around the country filled out detailed monthly surveys recording their work hours; frequency of shifts of more than 24 hours; and driving safety records, including car accidents, near-miss accidents (in which property damage was narrowly avoided) and incidents involving their falling asleep while driving or while stopped in traffic.
More than 17,000 surveys were collected between April 2002 and May 2003. Researchers also randomly selected 7 percent of study participants to keep daily work diaries that were verified through direct observation.
Study participants reported a total of 320 accidents during the 12-month study period, including 133 that resulted in treatment in the emergency room, property damage of more than $1,000 or the filing of a police report. Slightly more than 40 percent of the 320 crashes occurred on the commute from work.
Extended hours translate into dangerous driving
The study found that the majority of interns routinely worked more than 30 consecutive hours and reported they were awake 96 percent of their time in the hospital on average. Interns during the 12-month study period also reported working an average of 80 hours or more during 46 percent of workweeks and 100 hours or more per week during 11 percent of workweeks.
Every extended shift that was scheduled per month increased the monthly rate of accidents on the commute from work by 16 percent and the monthly rate of any car accident by 9 percent, the study found.
Interns also were more than twice as likely to fall asleep while driving or more than three times as likely to fall asleep while stopped in traffic in months in which they worked five or more extended shifts.
Eliminating extended shifts could mitigate accidents
While those findings are sobering, one research associate who helped conduct the study said there's one way to prevent, or at least mitigate, car accidents among medical interns.
"Because nearly 70 percent of medical interns who participated in the study commute to work by car, eliminating extended work shifts could prevent a substantial number of accidents," said Laura Barger, Ph.D., a research associate in medicine at the Brigham and Women's Hospital and Harvard Medical School.
Senior author Charles Czeisler, Ph.D., M.D., who leads the Harvard Work Hours, Health and Safety Group -- the team that conducted all three studies -- said it's simply unsafe to get behind the wheel of a car after working 24 hours straight.
"The health care profession has a duty to protect its young trainees from exposure to the well-known hazard of drowsy driving, which causes more than 100,000 motor vehicle crashes on our nation's highways ever year," Czeisler said.
Suggestions for improving shiftwork schedules
NIOSH, in its 1997 booklet "Plain Language About Shiftwork," offers the following recommendations for employers to mitigate the potential safety and health hazards of shiftwork schedules:
- Avoid permanent (fixed or non-rotating) night shifts.
- Keep consecutive night shifts to a minimum.
- Avoid quick shift changes.
- Plan some free weekends.
- Avoid several days of work followed by 4- to 7-day "mini-vacations."
- Keep long work shifts and overtime to a minimum.
- Consider different lengths for shifts.
- Examine start/end times.
- Keep the schedule regular and predictable.
- Examine rest breaks.
"Plain Language About Shiftwork" includes some basic facts about shiftwork, the health and safety effects of shiftwork, ways to improve shiftwork throughout the organization and coping strategies for the individual. It is available at http://www.cdc.gov./niosh/pdfs/97-145.pdf or by calling 1-800-35-NIOSH.