Priming system

A method of depleting a deleterious or undesirable substance from a patient's fluid comprising:

• passing a priming fluid through a bypass connected in parallel with an unprimed fluid treatment element,
• wherein the fluid treatment element includes at least one porous medium suitable for removing a deleterious or undesirable substance from the patient's fluid;
• exhausting the gas displaced by the priming fluid through a vent;
• passing the priming fluid through the fluid treatment element;
• withdrawing a fluid containing a deleterious or undesirable substance from a patient through the primed bypass;
• and
• then passing the patient's fluid through the primed fluid treatment element to deplete the deleterious or undesirable substance from the fluid.

A fluid processing device comprising:

• a fluid treatment element, which includes a porous medium;
• a bypass assembly connected in parallel with the fluid treatment element through a first junction and a second junction;
• a syringe in fluid communication with the second junction;
• and
• a gas outlet, which includes a bacterial barrier membrane, in fluid communication with the syringe through a vent junction.

A method for processing cerebrospinal fluid comprising:

• passing a priming fluid through a bypass connected in parallel with an unprimed fluid treatment element including at least one porous medium;
• venting gas;
• passing the priming fluid through the porous medium of the fluid treatment element;
• and
• passing cerebrospinal fluid through the bypass and then through the primed porous medium to treat the cerebrospinal fluid.