An object of the present invention is to provide a hollow fiber membrane with enhanced phosphorus-removing performance without impairing antithrombogenicity in order to inhibit in vivo accumulation of phosphate ions in living body that might cause bone metabolism disorders. The present inventors have found that a hollow fiber membrane having a specific membrane structure and a specific membrane composition possesses a very useful range for inner surface charges of the membrane. More particularly, the inventors have discovered that the above object can be achieved in a limited range in which the zeta potential on the inner surface of a hollow fiber membrane measured under given certain conditions is greater than −3.0 mV but less than 0 mV. This finding has led to the completion of the present invention.

A gas exchange system, said system comprising: a plurality of cartridges, each having a casing, said casing having a cartridge inlet adjacent to a first end and a cartridge outlet adjacent to an opposed second end; each casing having a bore in which is placed a gas permeable, liquid impermeable, hollow membrane; each hollow membrane having a membrane inlet arranged to receive a gas from an inlet chamber and a membrane outlet for venting said gas; each cartridge inlet in communication with a concentration zone, and arranged to receive a solvent from said concentration zone, so as to exit said solvent through said cartridge outlet; wherein said bore is arranged to flow said solvent adjacent to said hollow membrane so as to permit the exchange of gas through said gas permeable, liquid impermeable membrane.

A patient fluid removal compensation volume may be determined to make up for the patient fluid removal that does not occur during machine down times, and the patient fluid removal rate may be increased until the compensating volume is satisfied.

An oxygenator has a plurality of porous hollow fiber membranes comprising polypropylene for gas exchange, wherein each hollow fiber membrane has an inner surface that forms a lumen and an outer surface. The oxygenator is manufactured using a method which involves preparing a coating solution containing at least one compound selected from the group consisting of dopamine, salt of dopamine, and oligomer of dopamine; and bringing the inner surface or the outer surface of the hollow fiber membranes into contact with the coating solution for less than ten hours while blowing oxygen gas in the coating solution to form a dopamine polymer layer containing a polymer of the compound on the inner surface or the outer surface.