The service's chief financial officer Andrew Gay said the service was running at a $35 million deficit in December.

The $60 million appropriation in the mid-year budget was the biggest funding announcement in the mid-year budget update.

Mr Gray said without the extra money the service - which oversees Canberra Hospital - would have run out of money by the last quarter of the current financial year.

"The criticality would have been in the later part of the year," he told the hearing.

Health Minister Rachel Stephen-Smith said discussion about the desperate need for extra funding began in October.

It was known the service was running at a $30 million deficit in October.

The plea for extra cash came after the health service had completed a detailed analysis of its financial position.

Canberra Health Services CEO Bernadette McDonald said staff had been asked to find ways to trim the budget wherever possible.

"Some managers have taken it quite literally ... but from our perspective we've said just use common sense," she said.

While some staff have tried to cut down on the use of post it notes or stationery, she said there was no specific instructions to do that.

"We don't want to impact on patient care and we also don't want to make it extremely hard for people to do their job," Ms McDonald said.

Opposition Health Spokeswoman Vicki Dunne said the government had left the community in the dark, knowing the hospital was going to run out of money but failing to disclose it.

"Canberrans pay more than any other jurisdiction for health care and that price is going up," she said.

"Labor's chronic inability to manage money is putting patients at increased risk.

"When you can't manage money, you can't strategically invest in health services Canberrans need. ACT Labor is entirely responsible for Canberra's health crisis."