The volume of fluid removed from a patient during ultrafiltration is controlled automatically on the basis of central venous pressure measurements. At least one socket is positioned between the first connector and the second connector and is in electrical communication with the cable. The devices are typically catheter-based having an assessment mechanism fixed to a distal end of the catheter. The radio frequency generator delivers power in a range from about 50 kilowatts to about 2 Megawatts, and a power per unit length of antenna is in a range from about 0.