Patients have been told to stay away from hospital Emergency Departments during tomorrow's planned nurses strike unless attendance is "absolutely essential".
All EDs will be open but will have a much reduced number of nurses working with inevitable knock-on effects for how quickly patients can be seen.
Crucially, nurses will not be doing their normal triage duties where they carry out the initial assessment on newly arrived patients to determine the order in which they should be treated.
Children's emergency services are exempt from this part of the industrial action and the HSE said talks would continue at local level today and tomorrow to try to secure exemptions elsewhere but there are no guarantees of further concessions.
If the event of a major accident plan being activated in any part of the country, however, all nurses will respond.
Apart from the impact on EDs, effects of the strike will be felt primarily by some 2,000 people who were due to have elective procedures on the day, around 13,000 people who were due to have outpatients appointments and more than 10,500 people who would normally have contact with community health services.
Other patients and service users may find their appointments are delayed in the coming weeks as HSE staff try to reschedule those missing out tomorrow.
Liam Woods, HSE national director of acute services, said: "This will compromise our ability to attend to other patients in a timely manner."
The strike by some 40,000 members of the Irish Nurses and Midwives Organisation is over pay and conditions with concerns about the professions' ability to attract and retain staff.
If there is a breakthrough in talks today, some outpatient and community services may be restored and the HSE is adivising people to keep following announcements on news services and social media.
There is a small possibility that some elective procedures could also take place but patients are being told not to call the HSE as if there is any late change in plans, they will be contacted directly.