Abstract: The invention relates to a system of performing an evidence Dialysis modality of Batch, Tidal or a combination of both. The system: isolates cavity volume changes due only to ultrafiltrate; determines the volume of a patient cavity; determines a full cavity; determines an objective time to initiate an exchange; and determines an empty cavity. One or more combination of these features provide for evidence base Fill, Dwell, and Drain sequences. The system comprises: a cassette having a heated region and a sensor region for measurements. A valve manifold supplies a patient connection with fluid. A microprocessor receives pressure measurements, controls the heated region and activates a volumetric pump to deliver or extract discrete increments of the fluid to the cassette from bags. Filtering pressure measurements to remove rapid fluctuations determines an accumulated pressure in the patient cavity. The volume of fluid in the patient cavity correlates to the accumulated pressure.