Long work hours and unpredictable shifts can leave nurses so fatigued that they risk jeopardizing the safety of their patients, according to researchers at the University of Pennsylvania's School of Nursing.

The researchers found that nurses who worked more than 12 hours at a clip were three times more likely to make errors, such as giving the wrong medication or dosage, than nurses working eight-hour shifts. Putting in overtime at the end of a shift also increased the risk of errors.

The finding is especially important because of the national nursing shortage. Many hospitals have used mandatory overtime, the practice of forcing healthcare workers to stay beyond their scheduled shifts, as a way to cover staffing vacancies. The practice is not only controversial but potentially dangerous, the authors warn.

"When nurses are forced to work overtime after their already grueling shift, error rates soar and the quality of patient care declines precipitously," says AFT president Edward J. McElroy. "The findings of the University of Pennsylvania report are extremely important because nurses nationwide are faced with untenable working conditions."

The findings suggest that the routine use of 12-hour shifts should be curtailed, and overtime to compensate for the shortage of nurses should be eliminated, the researchers say.

The Penn study is one of the first national efforts to examine the effect of long hours and fatigue on nurses' performance on the job. The results of the study, based on logs kept by nurses who volunteered to participate, are reported in the July/August 2004 healthcare policy journal Health Affairs.

Data collected from 5,317 shifts revealed that nurses rarely left work at the end of their scheduled shift, even when scheduled to work 12 hours. In the four-week period studied, there were a total of 199 errors and 213 near-errors reported, most of which involved medication administration. Other mistakes included procedural, charting and transcription errors.

In recent years, AFT Healthcare locals have successfully lobbied for laws that prohibit mandatory overtime for health professionals in Connecticut, Maine, Maryland, New Jersey and Oregon.

"Despite their best intentions to stay with their patients as long as necessary, nurses are not immune to the effects of fatigue," says Ann E. Rogers, the lead author of the study and a nursing professor at Penn.