It also impedes “efficient clinical assessment”, causing clinicians to take longer performing tasks, and the “ability of staff to recognise a patient’s deteriorating condition”, he added.
“Care in corridors and other non-clinical spaces has been normalised, which in the opinion of the consultant who gave evidence is unsafe,” Me Regan said.
“When conducted routinely, care in corridors and other non-clinical spaces reduces the capacity of the emergency department.”
The chief executive will have 56 days to respond to the report.
Copies were also sent to the Welsh government, the chief executive of the Welsh Ambulance Services NHS Trust and the chief executive of Cardiff and Vale Health Board.
In December, the Welsh Ambulance Service declared a critical incident because of significantly increased demand and extensive handover delays.
The service, which covers more than three million people in Wales, said more than 340 calls were waiting to be answered at the time.
