Determining a Volume of Medical Fluid Pumped Into or Out of a Medical Fluid Cassette

• US 20150057601A1
• Filed: 08/21/2013
• Published: 02/26/2015
• Est. Priority Date: 08/21/2013
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Inventors: Ly, Tri, Zhu, Jie, Plahey, Kulwinder S.
• Granted Patent: US 10,117,985 B2
• Time in Patent Office: Days
• US Class Current: 604/28
• CPC Class Codes: A61M 1/1522 the interface being evacuated interfaces to enhance contact
• CPC Class Codes: A61M 1/1524 the interface providing means for actuating on functional elements of the cassette, e.g. plungers
• CPC Class Codes: A61M 1/154 with sensing means or components thereof
• CPC Class Codes: A61M 1/155 with treatment-fluid pumping means or components thereof
• CPC Class Codes: A61M 1/1561 at least one cassette surface or portion thereof being flexible, e.g. the cassette having a rigid base portion with preformed channels and being covered with a foil
• CPC Class Codes: A61M 1/1565 Details of valves
• CPC Class Codes: A61M 1/159 specially adapted for peritoneal dialysis
• CPC Class Codes: A61M 1/28 Peritoneal dialysis ; Other peritoneal treatment, e.g. oxygenation
• CPC Class Codes: A61M 1/281 Instillation other than by gravity
• CPC Class Codes: A61M 1/288 Priming priming in extracorporeal blood circuits A61M1/3643
• CPC Class Codes: A61M 2205/128 with incorporated valves
• CPC Class Codes: A61M 2205/3379 Masses, volumes, levels of fluids in reservoirs, flow rates
• CPC Class Codes: G01F 22/00 Methods or apparatus for measuring volume of fluids or fluent solid material, not otherwise provided for
• CPC Class Codes: G01F 22/02 involving measurement of pressure

Abstract

A method that includes pumping medical fluid out of or drawing medical fluid into a chamber of a medical fluid cassette, calculating a theoretical volume of fluid pumped out of or drawn into the chamber, and multiplying the theoretical volume of fluid pumped out of or drawn into the chamber by a correction factor to determine a corrected volume of fluid pumped out of or drawn into the chamber.

Claims

1. A method comprising:

(a) pumping medical fluid out of or drawing medical fluid into a chamber of a medical fluid cassette;

(b) calculating a theoretical volume of fluid pumped out of or drawn into the chamber; and

(c) multiplying the theoretical volume of fluid pumped out of or drawn into the chamber by a correction factor to determine a corrected volume of fluid pumped out of or drawn into the chamber.

2. The method of claim 1, further comprising multiplying the theoretical volume by the correction factor to determine an adjustment volume.

3. The method of claim 2, wherein the adjustment volume is added to the theoretical volume to determine the corrected volume.

4. The method of claim 1, wherein the medical fluid cassette comprises a flexible membrane that at least partially defines the chamber.

5. The method of claim 4, wherein the medical fluid cassette comprises a rigid base that cooperates with the flexible membrane to at least partially form the chamber.

6. The method of claim 5, wherein the medical fluid cassette comprises a fastening member attached to the flexible membrane, the fastening member defining a recess configured to receive a piston head of a medical fluid pumping machine, and the fastening member has an engagement surface that engages an engagement surface of the piston head when the piston head is disposed in the recess such that, when the piston head is disposed in the recess and is moved linearly away from the base of the cassette, the engagement surface of the piston head is engaged with the engagement surface of the fastening member and pulls the fastening member and the flexible membrane to which the fastening member is attached away from the base to increase a volume of the fluid pump chamber.

7. The method of claim 5, wherein pumping the medical fluid out of the chamber comprises driving the membrane of the medical fluid cassette to decrease a volume of the chamber and drawing the medical fluid into the chamber comprises driving the membrane of the medical fluid cassette to increase the volume of the chamber.

9. The method of claim 7, wherein the membrane is driven by a piston.

10. The method of claim 9, wherein the piston comprises a piston head attached to a piston shaft.

12. The method of claim 10, wherein at least a portion of the piston head has an outer diameter that is less than a maximum inner diameter of a recessed region of the rigid base that cooperates with the membrane to form the chamber.

13. The method of claim 1, wherein the method comprises pumping medical fluid out of the chamber of the medical fluid cassette by driving a piston against a membrane of the medical fluid cassette to decrease a volume of the chamber, calculating the theoretical volume of fluid pumped out of the chamber, and multiplying the theoretical volume of fluid pumped out of the chamber by the correction factor to determine the corrected volume of fluid pumped out of the chamber.

14. The method of claim 1, wherein the method comprises drawing medical fluid into the chamber of the medical fluid cassette by retracting a piston to pull a membrane of the medical fluid cassette to increase a volume of the chamber, calculating the theoretical volume of fluid drawn into the chamber, and multiplying the theoretical volume of fluid drawn into the chamber by the correction factor to determine the corrected volume of fluid drawn into the chamber.

15. The method of claim 1, wherein the method comprises repeating steps (a)-(c) multiple times during the course of a dialysis treatment and summing the determined corrected volumes to determine a total corrected volume of fluid pumped out of or drawn into the chamber over the course of the dialysis treatment.

16. The method of claim 15, wherein the dialysis treatment comprises pumping dialysate out of the pump chamber and into a peritoneal cavity of a patient multiple times and drawing dialysate out of the peritoneal cavity of the patient and into the pump chamber multiple times, and the method comprises carrying out steps (a)-(c) each time the dialysate is pumped out of the pump chamber and into the peritoneal cavity of the patient and each time the dialysate is drawn out of the peritoneal cavity of the patient and into the pump chamber to determine a total volume of dialysate delivered to the peritoneal cavity of the patient and a total volume of dialysate removed from the peritoneal cavity of the patient during the treatment.

17. The method of claim 1, wherein calculating the theoretical volume of fluid pumped out of or drawn into the chamber comprises determining a linear displacement of a piston.

19. The method of claim 1, further comprising measuring a pressure of medical fluid within the medical fluid cassette or within a fluid line connected to the medical fluid cassette.

20. The method of claim 19, further comprising isolating the pump chamber prior to measuring the pressure.

21. The method of claim 20, wherein isolating the pump chamber comprises closing valves adjacent first and second ports of the pump chamber.

22. The method of claim 20, wherein the pressure is measured a period of time after isolating the pump chamber.

24. The method of claim 20, wherein the pump chamber is isolated and the pressure is measured after drawing medical fluid into the pump chamber.

25. The method of claim 20, wherein the pump chamber is isolated and the pressure is measured after pumping medical fluid out of the pump chamber.

26. The method of claim 19, further comprising selecting the correction factor based on the measured pressure.

27. The method of claim 26, wherein the coefficient factor varies as a function of measured pressure for measured pressures between a first pressure value and a second pressure value, the first pressure value being less than the second pressure value.

30. The method of claim 27, wherein the coefficient factor is a first constant for all measured pressures that are less than or equal to the first pressure value and the coefficient factor is a second constant for all measured pressures that are greater than or equal to the second pressure value.

35. The method of claim 26, wherein the coefficient factor has a first value if the measured pressure is less than or equal to a first pressure value and the coefficient factor has a second value if the measured pressure is greater than or equal to a second pressure value.

36. The method of claim 35, wherein the coefficient factor has a third value if the measured pressure is greater than the first pressure value and less than the second pressure value.

37. The method of claim 35, wherein the coefficient factor has the first value for all measured pressures less than or equal to the first pressure value, the first value being a constant.

38. The method of claim 35, wherein the coefficient factor has the second value for all measured pressures greater than or equal to the second pressure value, the second value being a constant.

8. (canceled)

11. (canceled)

18. (canceled)

23. (canceled)

28. (canceled)

29. (canceled)

31-34. -34. (canceled)

39-42. -42. (canceled)

43. A medical fluid pumping system comprising:

a medical fluid cassette comprising a flexible membrane that at least partially defines a pump chamber; and

a medical fluid pumping machine defining a compartment configured to receive the medical fluid cassette, the medical fluid pumping machine comprising

a piston that is aligned with the pump chamber of the medical fluid cassette when the medical fluid cassette is disposed within the compartment, the piston being operable to pump medical fluid out of or draw medical fluid into the pump chamber of the medical fluid cassette; and

a control unit that is operable to calculate a theoretical volume of fluid pumped out of or drawn into the pump chamber and is operable to multiply the theoretical volume of fluid pumped out of or drawn into the pump chamber by a correction factor to determine a corrected volume of fluid pumped out of or drawn into the pump chamber.