TORONTO — Nearly one-fifth of the nurses in hospitals across the country acknowledge making errors when giving patients medications, with understaffing and working too much overtime primarily blamed for the likelihood of those mistakes occurring, a report by Statistics Canada says.

In its report released Wednesday, Statistics Canada said that in settings in which nurses ended up working beyond their regular shifts due to understaffing and inadequate resources, patients were more likely to receive the wrong medication or dosage.

The study is based on findings from a 2005 survey of 19,000 nurses, which found 19 per cent of respondents reported having made "occasional" or "frequent" drug errors in the previous year while caring for patients.

The study found there was a strong link between medication mistakes and workplace organization and environment, including covering some nursing shifts through overtime, increasing workload, perceived staffing shortages, unsupportive colleagues and poor on-the-job relations with doctors.

"The study is very clear that these errors are not related to the nurses' experience or level of education and that these are truly related to aspects of the work environment," said Lisa Little, acting director of public policy for the Canadian Nurses Association.

"And these aspects are things around role overload, which means that nurses are caring for many more patients than they used to," she said Wednesday from Ottawa.

"So nurses may have had five patients in a medical ward to look after and now they're looking after eight or nine patients. And what does that mean about the time that you have to spend with patients and the quality of care and how rushed you are that can lead to those kinds of errors happening?"

The survey found that nurses face a broad range of physical and emotional challenges in a demanding and often hectic workplace.

"It validates what we know that nursing work environment is inadequate to support quality patient care, so too often nurses are having to work in situations where they're understaffed, where they're working overtime, where they may not have the resources they need," said Prof. Diane Doran, who specializes in patient health at the University of Toronto's faculty of nursing.

"So your workload is higher than what is optimal, and it's a combination of those factors that leads to bad outcomes like medication errors," she said.

The study found that among registered nurses who routinely worked overtime, 22 per cent reported making medication mistakes, compared with 14 per cent of those who did not work extra hours.

"Nurses who are, I don't want to say forced, but are strongly encouraged to come in on their days off and work overtime because they're short-staffed, there's an element of fatigue that probably comes into play on this," said Little, adding that appropriate levels of work hours for nurses need to be looked into.

Dealings with physicians also appeared to affect performance: among nurses whose working relations with doctors were least favourable, 27 per cent reported medication error, compared with 12 per cent among those with good nurse-doctor interactions.

Little said the study showed that most respondents reported good on-the-job rapport with doctors.

"I think that perhaps when there is not a good collegial relationship, the nurses may not feel comfortable to go back and approach the physician to say: 'I'm not really sure what you said there. Can you clarify that."'

The study also found that nurses who perceived they were not getting enough support from co-workers were significantly more likely to report medication errors than were those who felt more bolstered by colleagues.

Low co-worker support might result from inadequate staffing as busy and stressed nurses may be less able or unwilling to help their colleagues, the study authors suggested.

Linda McGillis Hall, associate dean of research for the University of Toronto's nursing department, said she is in the midst of studying the impact of interruptions faced by hospital RNs as they care for patients.

Those concentration-destroying disturbances can include questions from co-workers, meeting demands from patients and the general hubbub of a hospital ward - from the sounds of call bells and pages to noisy equipment.

"When a nurse is preparing a medication and trying to think it through and drawing it up, if you have all kinds of environmental noise, that can cause interruptions as well," McGillis Hall said.

"One of the things we found when I did a pilot test was when nurses were interrupted it was leading to medication errors or delays in procedures or treatments or delays in medication."

Little said there is a nursing shortage across the country that affects hospitals and other health-care facilities, both large and small.

"It's systemic," she said.

"Nurses are telling us it's not healthy for the patients, it's not healthy for them ... they're committed to their patients, but they need the support of the employer and work environment to help them do their jobs safely and effectively."

McGillis Hall said the fact that nurses are admitting to medication errors should be seen as a good thing by the public.

"I think it's really important that we have a climate or a culture where people do come forward and identify errors," she said.

"It means that health-care workers, nurses in particular, are becoming more transparent, and that means they're reporting them and organizations are trying to respond and do something about it."