A hospital has made changes after two patients were accidentally given medical air instead of oxygen.
The two incidents, which took place at the Norfolk and Norwich University Hospital (NNUH), were classed them as "never events" meaning they were serious but preventable.
They happened to patients in November who were being handed over to the hospital by the East of England Ambulance Service.
The patients should have been given oxygen but were given medical air instead which only contains 20pc oxygen.
The ambulance service said in a message to staff: "Severe harm or death can occur, if medical air is accidentally administered to patients instead of oxygen.
"As per NNUH's request, with immediate effect, when handing over at the NNUH, all medical equipment and oxygen should be swapped only by an emergency department doctor or registered nurse."
A spokesman for the NNUH said no harm was caused to the two patients.
An EEAST spokesman said: "The hospital's senior clinical and management team have put in place new procedures regarding hospital oxygen supplies.
Although no patients were injured in these incidents, we take all patient safety matters seriously and, in compliance with the NNUH's procedures, we have published an operational instruction requiring EEAST staff to not connect patients to the hospital oxygen supply on handover."
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