WASHINGTON -- The Institute of Medicine says doctors in medical residency programs are working too many hours and putting patients at risk. The problem is fatigue-related mistakes. Now the institute recommended limiting hours for doctors-in-training.

The study was requested by members of Congress who are concerned about the threat to patient safety when doctors don't get enough rest.

Medical residents endure 80 hour work-weeks, routinely spending 30 hours on duty at a time. It's a grueling schedule Dr. Marco Cavagna said he is all too familiar with.

"There's certainly a point of diminishing returns. People start thinking less clearly after you've been up a particularly long time," Cavagna said.

An 18-month study by a panel of medical experts shows the chronic sleep deprivation doctors-in-training often suffer through can lead to mistakes.

"We want to eliminate tired, fatigued residents from being in the position of delivering healthcare," said committee chairman Dr. Michael Johns.

So the committee is recommending medical trainees work no more than a 16-hour shift with at least a 5-hour rest period before the next shift begins.

"We think protected sleep is necessary if you're going to work 16 hours straight," said Brian Lindberg, with the Consumer Coalition for Quality Healthcare.

But Cavagna said he worries limiting hours might hurt continuity of care. He said patients benefit when the doctors who admitted them can spend as much time as possible caring for them.

"It is virtually impossible, no matter how succinct you are or how thorough you are to just deliver everything to the next person that's going to come in on call," Cavagna said.

It is not known just how many patients die every year from fatigue-related errors because there's no national reporting system which is something patient advocates said they want to change.

"That evidence does not seem to exist," said David Dinges, with the University of Pennsylvania School of Medicine.

In addition to work hour changes, the panel also recommended limits on patient caseloads and more supervision of medical residents.

There will be some costs associated with implementing the recommendations. The panel said some of the workload will need to be shifted to other personnel so teaching hospitals will need to hire more staff. They put the cost at just under $2 billion. Where the money would come from wasn't part of the study.

A congressional committee requested the study and is urging the medical community to implement the recommendations.