Routine operations have been cancelled for a second day in a row by one health board.
Hywel Dda University Health Board said the continued cancellations were “in the interest of patient safety”.
Operations were cancelled at Bronglais, Glangwili, Prince Philip and Withybush hospitals in mid and west Wales on Monday and Tuesday.
Medical director Dr Phillip Kloer apologised and said there had been more ill patients than last year.
He added: “Last year we were able to carry on operating through the winter months but this year it has been even more challenging and I really want to thank our staff on the front line who’ve gone the extra mile.
“At the moment though the hospitals are under significant pressure – all four of our hospitals – so it will take a few weeks naturally to get back to that routine business.”
All outpatient appointments are continuing as normal.
The health board said emergency surgery and urgent cases were not being cancelled whenever possible and day surgery was continuing everywhere but Bronglais Hospital.
Affected patients are being directly contacted.
“This situation remains challenging with the health board operating in line with our escalation procedures to help manage patient flow and maintain patient safety,” a spokesman said.
The Community Health Council said about 30 to 33 operations were cancelled on Monday across the four hospitals.
The British Medical Association in Wales said it was concerned lives could be needlessly lost unless there was urgent action to tackle winter pressures.
Its consultant committee chairman Dr Phil Banfield said members were “extremely concerned about the current pressures facing the Welsh NHS”.
“Patients are being left in an intolerable situation and care will suffer if something isn’t done about this now,” he added.
First Minister Mark Drakeford said “there were very few operations scheduled this week” and this week was “always the busiest week for unplanned admissions to our hospitals”.
He said the system “has proved resilient” to pressures in the past two weeks “because of the plans put in place by the health boards, supported by the Welsh Government and that additional investment we have put in place”.
The health board plans to implement its broader winter plan, designed to help reduce demand for hospital admission and prioritise patients for care at home over the winter period.
“Over the next few weeks, a number of staff taking on new and different roles will be coming into post to support patients to receive the most appropriate care for their needs in the most appropriate setting,” the health board said.
“These are resourced through the winter planning monies supported by Welsh Government, in addition to the money we invested ourselves as a health board.”
Richard Johnson, director of the Royal College of Surgeons in Wales, said cancelling planned operations and delaying treatment was “unfair and potentially devastating for patients”.
“We need to find a long-term solution to restore their right to timely treatment,” he added.
Helen Whyley, director for the Royal College of Nursing in Wales, said the NHS in Wales was under more pressure than ever.
“What it means is, on the frontline for staff every day, it is a real battle to make sure patients get the care they require,” she said.
She called for “everyone to get back in the room” to see “what more can be done to make sure these pressures are alleviated” across Wales.
Hywel Dda said on Monday that “critical pressures” had been felt across A&E departments, GPs and community services over the weekend.
Ceri Phillips, a professor of health economics at Swansea University, said “winter pressures are not new” but unplanned hospital admissions were “very difficult to plan for”.
What are winter pressures?
Although the NHS is under pressure all year round, the period after Christmas and the first few weeks of new year is often the most difficult as staff try to deal with significant numbers of seriously ill patients.
There are several reasons for this – as a result of the festive season’s bank holidays, there has been reduced access to community services such as GPs and social care, which can cause logjams to develop in hospitals.
During the holiday period, people might also put off getting a potential health problem checked out.
Pressures are also caused because of winter bugs, with the current flu season already looking worse than last year.
The Welsh Government said it had given £30m to health boards to provide extra capacity this winter.
Helen Mary Jones, Plaid Cymru’s spokeswoman on health and AM for Mid and West Wales, said added pressure, such as hospital patients unable to be discharged into the community, had created “a real crisis” for staff and patients in Hwyel Dda health board area.
She said Wales’ health boards should be allowed to share staff to pool resources.
“We spend a huge amount of our budget on health, rightly, here in Wales… and we are still not getting it right and that can’t be allowed to carry on,” she said.
Figures published last month showed accident and emergency performance at hospitals in Wales was at a record low for the third month running and the Welsh Ambulance Service failed to meet its response time target for the first time in four years.
Angela Burns, the Welsh Conservatives’ shadow health minister, said: “It seems that Wales’ NHS suffers from extraordinary pressures month in, month out.”
Cardiff and Vale health board and Swansea Bay health board said services were busy but planned operations were continuing as usual.
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