Determining a volume of medical fluid pumped into or out of a medical fluid cassette

• US 10,117,985 B2
• Filed: 08/21/2013
• Issued: 11/06/2018
• 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.
• Primary Examiner(s): Mehta, Bhisma
• Assistant Examiner(s): Frehe, William
• Application Number:
  US13/972,498
• Publication Number:
  US 20150057601A1
• Time in Patent Office: 1,903 Days
• 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 a medical fluid out of or drawing a medical fluid into a chamber of a medical fluid cassette such that a pressure of the medical fluid in the medical fluid cassette causes a membrane of the medical fluid cassette to bulge around a perimeter of a piston head;

(b) calculating, by a processor, a theoretical volume of the medical fluid pumped out of or drawn into the chamber;

(c) measuring the pressure of the medical fluid within the medical fluid cassette or within a fluid line connected to the medical fluid cassette;

(d) selecting a correction factor based on the measured pressure, the correction factor corresponding to an amount of bulging of the membrane of the medical fluid cassette;

(e) multiplying, by the processor, the theoretical volume of the medical fluid pumped out of or drawn into the chamber by the correction factor to determine an adjustment volume; and

(f) determining a corrected volume of the medical fluid pumped out of or drawn into the chamber based on the adjustment volume.

2. The method of claim 1, wherein the adjustment volume is added to the theoretical volume to determine the corrected volume.

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

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

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

6. The method of claim 1, further comprising isolating the chamber prior to measuring the pressure.

7. The method of claim 6, wherein isolating the chamber comprises closing valves adjacent first and second ports of the chamber.

8. The method of claim 6, wherein the pressure is measured a period of time after isolating the chamber.

9. The method of claim 6, wherein the chamber is isolated and the pressure is measured after drawing the medical fluid into the chamber.

10. The method of claim 6, wherein the chamber is isolated and the pressure is measured after pumping the medical fluid out of the chamber.

11. The method of claim 1, wherein the correction factor varies as a function of the 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.

12. The method of claim 11, wherein the correction factor is a first constant for all measured pressures that are less than or equal to the first pressure value and the correction factor is a second constant for all measured pressures that are greater than or equal to the second pressure value.

13. The method of claim 1, wherein the correction factor has a first value if the measured pressure is less than or equal to a first pressure value and the correction factor has a second value if the measured pressure is greater than or equal to a second pressure value.

14. The method of claim 13, wherein the correction factor has a third value if the measured pressure is greater than the first pressure value and less than the second pressure value.

15. The method of claim 13, wherein the correction factor has the first value for all measured pressures less than or equal to the first pressure value, the first value being a constant.

16. The method of claim 13, wherein the correction factor has the second value for all measured pressures greater than or equal to the second pressure value, the second value being a constant.

17. The method of claim 1, wherein the medical fluid cassette is a peritoneal dialysis fluid cassette and the medical fluid is a dialysis fluid.

18. The method of claim 17, wherein the dialysis fluid is pumped out of the chamber and delivered to a peritoneal cavity of a patient.

19. The method of claim 17, wherein the dialysis fluid is drawn into the chamber from a peritoneal cavity of a patient.