Alberta Health Services is promising patient safety won't suffer under hospital reforms which will see health-care aides take on a much larger role.

"We've worked with the care providers to establish a set of indicators that we'll look at in real time and we're working to make sure we've got safety nets in place in case we need to enact them," said Deb Gordon, AHS chief nurse.

The reform is part of an effort to keep the cost of health care in Alberta sustainable, the province said.

The United Nurses of Alberta said the number of registered nurses will be reduced by half in some units, with duties taken up by lesser-trained and lower-paid health-care aides.

Part of the problem is that there are no professional standards or requirements for aides who need only take a six-month college course, or be trained in house, nurses say.

AHS won't reveal how many RNs will be on each hospital unit after the transition, but the United Nurses of Alberta says it has been told that medical units at the University of Alberta Hospital will have two RNs on each shift, down from three.

In some cases, a licensed practical nurse may be added, but more often health-care aides will be hired.

"There'll be mistakes made," said veteran nurse Mary Jane Winch. "I mean there are mistakes made by RNs as well, but with less training there's more mistakes and that's a big fear."

Gordon said the province is working on those concerns.

"We've just started on this journey." she said. "(We) still need to evaluate how it all works out and need to tweak it, along the way, so it wil be a period of years before this transformation is complete, but we need to start now."

AHS maintains it is not replacing nurses with aides and while it has laid off about 200 registered nurses over the past few months, most of those have been offered news jobs.

AHS also says there are currently job postings for 300 registered nurses across the province.

With files from CBC's Kim Trynacity