Thousands of patients around the country have been impacted by a fourth day of disruption to health services.
The cancellation of appointments is adding to an already significant backlog of cases in the public system as a result of the pandemic.
Cora McNally's 20-year-old daughter has special needs and has been waiting several months for an MRI scan on her leg.
Ms McNally said she checked if the scan would proceed this morning, only for it to be cancelled later, due to difficulties with the computer system at University Hospital Galway.
She said her daughter is anxious as a result of the cancellation and in a lot of pain.
She contends that had she been told in advance that the scan would not proceed, it would have eased the burden. Now, today's events have things "up in a fizzle".
Ms McNally said the impact of the malware attack is hugely frustrating for her daughter and the effort to resolve the difficulties she’s experiencing.
The CEO of the Saolta Hospital Group, Tony Canavan, said people with appointments should assume they are cancelled, unless they hear otherwise.
He said there has been a very significant impact on hospitals in the west and north west, with just chemotherapy, maternity and dialysis services unhindered.
He said the hospitals in the region expect to have "significant problems" for the remainder of the week.
Mr Canavan said he was particularly concerned for patients, many of whom have already experienced delays for treatment or diagnostic services as a result of the pandemic.
The upheaval being experienced in the west has been replicated elsewhere.
This afternoon in the Ballyfermot area of Dublin, Natasha White said she was furious at the fact that her son's appointment was cancelled. And she said the problem was compounded by the lengthy delays many experienced in order to be seen in the first place.
Ms White was meant to be bringing her 13-year-son to a hospital appointment at Crumlin Children's Hospital's rheumatology department today.
Andre, who has Down Syndrome, was diagnosed with an aggressive form of arthritis nearly five years ago.
His mother said doctors are still trying to figure out what medication works best to relieve some of the discomfort.
''Last October, [the doctors] changed his medication and we were supposed to be seen in January to review the situation but because of the backlog with appointments, we didn't get seen.
"That meant a lot of ringing around trying to get this appointment for today. It was only confirmed last week and I was absolutely delighted because his medications are not working.''
But Andre's appointment, like thousands of others, did not go ahead.
''I'm so annoyed and upset for Andre because he's the one living with this pain on a daily basis," Ms White said.
"His mobility is gone downhill, he finds everyday things very heard. Now going out on his scooter, or his bike, even for walks, cause him an awful lot of pain''
She wants an appointment as soon as possible, but right now, there is no certainty. ''I don't know when we're going to be seen,'' she says.
Additional reporting: Conor Hunt
