Hospitals are warning of potential disruption to services once they get back up and running later.
Industrial action by nurses ends at 8am but there is no sign of any breakthrough in the dispute between their unions and the Government.
Yesterday, 37,000 nurses walked off the job and onto the picket line.
That action ends at 8am.
While contingency arrangements were put in place, 25,000 patients had their appointments cancelled.
The HSE says there could be a surge in patients in emergency departments today due to people who may have stayed away yesterday.
It says having full staff working will help with the surge.
But it is far from the end of the industrial action as the nurses dispute with the government over pay and staffing is no closer to being resolved.
The INMO is planning a further five 24-hour stoppages, beginning next Tuesday.
Liam Woods, HSE Director of operations, says preparing for that begins today: "We will be getting into discussion with the INMO in terms of the potential action next Tuesday following that we will be advising hospitals in terms of elective work for next week.
Separately, 6,000 psychiatric nurses will refuse to work overtime today and tomorrow as they too are on a collision course with the government.
