A continuous renal replacement therapy (CRRT) device is provided that weighs between 2 and 10 pounds. The CRRT device can be portable, mobile or completely worn on the person of the patient. Blood and dialysate are each pumped in a pulsed or pulsatile manner through a dialyzer such that a significant portion of the peak pulse of the blood flow coincides with a significant portion of a low pulse portion of the dialysate flow. An differential pressure between a dialysate inlet of the dialyzer and the blood inlet of the dialyzer periodically changes from a high differential pressure of between 70 and 120 mmHg for a first time period and a low differential pressure of between −10 and 10 mmHg for a first time period and a low differential pressure of between −10 and 10 mmHg for a second time period. The frequency of the high and low differential pressure cycle is between about 0.5 and 4 Hz.
