Patient fluid management is carried out by separating plasma from whole blood in vivo via an implantable filter device comprising one or more elongated hollow tubes and a plurality of elongated microporous fibers having an interior lumen extending along the length thereof, each fiber having a first and second end secured to the one or more elongated hollow tubes by passing plasma through the fiber wall from the outer wall surface to the inner wall surface and to the interior fiber lumen, directing the separated plasma to an ultrafiltration apparatus having a sieving coefficient cutoff between about 1.times.10.sup.4 and about 6.times.10.sup.4 daltons, separating plasma water and selected plasma components, from the separated plasma, and directing the treated plasma to the patient.