The HSE has defended the use of non-critical care nurses in intensive care units (ICUs) saying it is "better than the alternative".
Ireland's ICUs are coming under huge pressure due to the surge in admissions of patients with Covid-19.
Last night there were 169 people in ICU as well as around 210 patients in ordinary wards who require non-invasive advanced respiratory support.
The Herald yesterday reported on the concerns of senior ICU medics that non-specialist staff were being deployed to help the most critically ill patients.
Dr Enda O'Connor, director of ICU in St James's Hospital said he was happy to have the staff - who have been given training in the core aspects of ICU care - but they are "working outside their comfort zones".
At the Mater Hospital, Serena O'Brien, clinical nurse manager in critical care, hospital said the situation is "scary".
She spoke of how critical care nursing is a highly skilled profession and said: "You are asking a nurse to come in and look after a ventilator.
"They have never seen one. They haven't a clue. How would they?
"They have a different skillset out on the ward."
At a HSE press conference the organisation's chief clinical officer, Dr Colm Henry said the core capacity in ICU is 286 beds and that there is up to 350 available to cater for a surge in admissions.
He said the HSE believes the same quality of care can be provided for if the full 350 capacity is used, but it is reliant on redeploying staff from other services.
Dr Henry added: "Clearly we would be in a better position if we never had to expand intensive care capacity to go into surge with Covid-19."
But he said the development of that capacity with redeployed staff "enables us to provide care".
"It's better than the alternative," he said.