Methods for ultrafiltration control in hemodialysis

A method of increasing the accuracy of the removal of volumes of fluid from a patient during a dialysis session, said session having a predermined target of volume of fluid to be removed from the patient during the dialysis, said method performed in a dialysis machine having an ultrafiltration pump, a dialysate circuit and an ultrafiltration tank for receiving fluids from said dialysate circuit commensurate with the fluid removed from the patient, comprising the steps of:

• prior to conducting dialysis of said patient,
• (a) pumping dialysate through said dialysate circuit with said ultrafiltration pump, said dialysate circuit comprising a closed volume fluid circuit;
• (b) measuring the flow rate of said dialysate with a flow meter in said dialysate circuit;
• (c) calibrating said ultrafiltration pump from said measured flow rate;
• and thereafter
• conducting dialysis of said patient;
• and
• during dialysis, pumping dialysate from said dialysate circuit with said ultrafiltration pump into said ultrafiltration tank in accordance with said predetermined target of volume of fluid to be removed from the patient.

A method of increasing the accuracy of fluid removal from a patient during dialysis, said method performed in a dialysis machine having dialyzer, a dialysate circuit, an arterial line conducting blood from the patient to said dialyzer and a venous line conducting blond from said dialyzer back to said patient, comprising the steps of:

• prior to dialysis,
• (a) conducting blood from the patient into the blood side of said dialyzer;
• (b) measuring the blood pressure in the inlet and outlet sides of said dialyzer;
• (c) measuring the fluid pressure in the dialysate circuit;
• (d) computing the average blood pressure in the dialyzer from said measured blood inlet pressure and said measured blood outlet pressure;
• (e) comparing said average blood pressure with said measured pressure in said dialysate circuit;
• and responsively
• (f) adjusting the fluid pressure of said dialysate circuit to substantially match said average blood pressure;
• wherein said step of adjusting the fluid pressure in said dialysate circuit comprises the step of:
• pumping fluid between said ultrafiltration tank and said dialysate circuit, whereby pumping fluid from said ultrafiltration tank into said dialysate circuit increases the pressure in said dialysate circuit, and pumping dialysate from said dialysate circuit into said ultrafiltration tank decreases the pressure in said dialysate circuit;
• and thereafter
• pumping dialysate through the dialysate side of said dialyzer to dialyze the patient's blood;
• and
• pumping dialysate from said dialysate circuit into said ultrafiltration tank;
• whereby the volume of fluid pumped into said ultrafiltration tank during dialysis closely approximates the volume of fluid removed from said patient due to the balance of pressure between said blood side and said dialysate side of said dialyzer.

A method of testing the integrity of an ultrafiltration system, said method performed in a dialysis machine having an ultrafiltration pump, a dialysate circuit comprising a closed fluid system and having a tank containing a batch of dialysate, and an ultrafiltration tank for receiving fluids from said dialysate circuit commensurate with the fluid removed from a dialysis patient, comprising the step of:

• prior to dialysis,
• (a) filling said dialysate circuit substantially completely with fluid;
• (b) filling said ultrafiltration tank at least partially with fluid;
• (c) pumping fluid from said ultrafiltration tank into said dialysate circuit;
• (d) measuring the fluid pressure in said dialysate circuit in response to said pumping of fluid from said ultrafiltration tank into said dialysate circuit, the maintenance of an increase in pressure indicative of the integrity of said ultrafiltration system, and thereafter
• conducting dialysis of said patient;
• and
• pumping dialysate from said dialysate circuit into said ultrafiltration tank.

A method for improving the ultrafiltration control of a dialysis patient, comprising the steps of:

• providing a volumetrically closed and substantially noncompliant dialysate circuit comprising a substantially noncompliant dialysate solution tank and a volumetrically closed dialysate flow path for circulation of a dialysate solution to a dialyzer having a blood side and a dialysate side;
• providing an extracorporeal circuit for conducting blood from a patient to said blood side of said dialyzer and back to said patient, said blood creating a fluid pressure in said blood side of said dialyzer;
• filling said dialysate solution tank and said dialysate flow path with said dialysate solution and circulating said dialysate solution through said dialysate circuit, said dialysate solution creating a fluid pressure in said dialysate side of said dialyzer;
• providing an ultrafiltration pump in said dialysate circuit for removal of said dialysate solution from said dialysate circuit and calibrating said dialysate pump during said step of circulating said dialysate solution through said dialysate circuit;
• immediately prior to commencing or terminating a dialysis session, balancing the fluid pressure in said dialysate side of said dialyzer with the fluid pressure in said blood side of said dialyzer by transferring fluid between an ultrafiltration tank and said dialysate circuit with said ultrafiltration pump to thereby raise or lower the pressure in said dialysate circuit;
• during dialysis, removing a portion of said dialysate solution from said dialysate circuit in accordance with said ultrafiltration pump and storing said removed portion of said dialysate solution in said ultrafiltration tank.