Procedure to increase the safety of a device for extracorporeal blood treatment, which presents a blood inlet tube, which leads from the patient to the entrance of a first chamber of an exchange unit divided by a semipermeable membrane in the first and a second chamber and a blood outlet tube leading from the exit of the first chamber to the patient, an ultrafiltration equipment, to extract a total volume of UFVges ultrafiltrate prescribed from the first chamber of the exchange unit with a UFR ultrafiltration coefficient ( t) during a predetermined time of the UFT treatment, a unit of measurement to determine the volume of the BV blood or a magnitude of the patient's measurement that correlates with the volume of the blood and a regulation unit to prescribe a UFR ultrafiltration coefficient (t) depending on the volume of BV blood, with the following stages of the procedure: determination of an upper limit value for the ultrafiltration rate UFR (t) and limitation of the filtration coefficient UFR (t) prescribed by the regulation unit to the upper limit value UFRlim when the ultrafiltration coefficient UFR (t) prescribed by the calculation unit reaches the value upper limit UFRlim, characterized in that the upper limit value UFRlim is determined from the total ultrafiltration volume UFVges prescribed and the duration of the prescribed UFT treatmentProcedimiento para aumentar la seguridad de un dispositivo para el tratamiento extracorpóreo de la sangre, quepresentaun tubo de entrada de la sangre, que conduce desde el paciente a la entrada de una primera cámara de unaunidad de intercambio dividida mediante una membrana semipermeable en la primera y una segunda cámara yun tubo de salida de la sangre que conduce desde la salida de la primera cámara al paciente,un equipo de ultrafiltración, para extraer un volumen total de ultrafiltrado UFVges prescrito de la primera cámarade la unidad de intercambio con un coeficiente de ultrafiltración UFR(t) durante un tiempo del tratam
