Covid-19 patients have been transferred "hundreds of kilometres" to get to an ICU bed.
The Clinical Director of the Mobile Intensive Care Ambulance Service said that 40 critically ill patients have been moved between hospitals this month so far, including 17 this week.
Dr David Menzies said the majority of the patients have Covid-19 and were being transferred because there wasn't an intensive care bed available in the hospital they were in.
The service is already twice as busy as it was last January, and as hospitals and ICU operate in surge capacity, its role has become even more vital.
"We have transferred patients within Dublin, according to their capacity and needs on the day. We have also transferred patients hundreds of kilometres for ICU beds. We are in surge capacity, we can go to nearly 350 beds, we are almost there and we are feeling the pinch", said Dr Menzies.
He said there are around 20 ICU beds available in the system today.
"They're all over the country and patients who need them may not be in the same place so we are transferring patients long distances to access ICU beds."
MICAS is one of three critical care response services within the National Ambulance Service, with teams in Dublin, Cork and Galway serving the whole country.
Before the pandemic, its normal work was to move patients to specialist centres for specialist care.
"In the pandemic, we've moved a huge amount of patients due to ICU capacity issues."
It has also moved critically ill non-Covid patients into private hospitals to alleviate pressure in acute hospitals.
The crews can provide the same level of ICU care on the move as in the traditional intensive care units.
They are kitted out with more than 9,000 litres of oxygen, intensive care monitoring systems, a ventilator and infusion pumps, and are staffed with a combination of staff from the National Ambulance Service and doctors and nurses from hospitals.
A team that travels with the patient includes an emergency medical technician, critical care doctor and nurse.
Some of the critical care staff involved can be seconded from hospitals to do this or work on rotation.
However, as the pandemic progressed and hospitals ICUs became busier, the service trained up extra critical care paramedics as well.
"After the first wave, which was not as bad as this, it was recognised there would be challenges in accessing ICU beds, in staffing them, and at the same time there would be an increase in demand for our service and it was going to be the same group of people trying to provide all that."
Dr Menzies said the service is coping while providing this support to hospitals and patients, but that "it's not an infinite resource".
"Both in the ambulances and the intensive cares, we are reaching the limit of what we can provide, even by moving those patients between hospitals."
He implored people to stay at home.
"We are right to the pin of our collar here in terms of critical care. There is very little more available, and there is no plan B. We have to stay at home," he said.