Abstract: A device and a procedure for the extemporaneous preparation of an individual quantity of sterile treatment fluid that may be compressible, in particular a treatment gas, the device comprising a rigid cartridge (3) with an outlet valve, an administration syringe (4) and a filtration-type connection/sterilization device (5, 6). The cartridge (3) simply contains an individual quantity of treatment fluid under pressure, and the cylinder of the syringe (4) is adapted to contain this individual quantity.