There are fears oxygen at Altnagelvin hospital may have to be rationed.
It comes as hospitals in Northern Ireland were operating at above-capacity due to the number of patients with Covid-19.
Altnagelvin is using between 800 and 900 litres of oxygen every minute, which is three times higher than the normal level.
A member of the board which manages the hospital has told the BBC that there is not enough oxygen to treat patients.
A green, amber and red alert system is in place to monitor oxygen levels - and the past week it has been moving towards red.
The North's Chief Nursing Officer says the supply of oxygen to hospitals in Northern Ireland is monitored daily, and mitigation measures are in place if the high level of demand continues.