Larger hospitals have a LOX (Liquid Oxygen) storage tank with evaporator which feeds the internal ring main with gaseous oxygen. The tank is topped up by visiting road LOX tanker truck.
There is usually a gaseous oxygen charging point(s) for refilling portable O2 cylinders manned my hospital technicians.
Be aware that gas cylinders require a periodic pressure test, usually 5 yearly from the date of first charge stamped on the neck of the cylinder. The correct current colour code is green with white neck.