A paramedic with East Midlands Ambulance Service (EMAS) has said crews do not have enough time to prepare their vehicles in between calls.
It means that portable oxygen cylinders are often so depleted by the end of the week that paramedics sometim
es cannot give patients the care they need.
Ambulances in Northamptonshire have even had to arrange to meet crews from quieter areas of the county to transfer oxygen to the busier vehicle.
The paramedic, who did not want to be named, told the Chronicle & Echo: "When we see a patient in their home, we often want to make them stable where they are before taking them to the ambulance, but we are sometimes not getting the option.
"You are always thinking about whether to hold a bit back in case someone later on will have to go without. The point is that patient care is not the priority; getting to jobs within the 18-minute target time is the only thing that seems to matter."
Oxygen for the use of ambulance crews is delivered to Northampton General Hospital and other stations around the county by British Oxygen. Crews are ideally supposed to fill their cylinders between jobs but they say a low number of ambulances in service means they get fewer chances to do so or perform other checks.
Although the ambulances always carry one large cylinder of oxygen it is not suitable to be carried to an emergency patient.
The paramedic said: "The big one is about 50 kilos so it's not much use if you need to take it quickly to someone who's broken his leg on a rugby pitch."
A spokesman for EMAS said crews had not so far raised the problem obtaining supplies of oxygen with its management team.
He said: "If crews need re-supplying, the procedure is for them to request to return to base.
"A well-established contract and process for the replenishment of all medical gases is in place."
nick.spoors@northantsnews.co.uk
The full article contains 366 words and appears in Northampton Chron & Echo newspaper.