Method and device for calculating dialysis efficiency

• US 6,258,027 B1
• Filed: 11/30/1999
• Issued: 07/10/2001
• Est. Priority Date: 06/02/1997
• Status: Expired due to Term

• Current Assignee: Gambro Lundia AB (Baxter International Inc.)
• Original Assignee: Gambro Lundia AB (Baxter International Inc.)
• Inventors: Sternby, Jan
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): CARTER, RYAN CHRISTOPHER
• Application Number:
  US09/424,900
• Time in Patent Office: 588 Days
• Field of Search: 600/309, 600/366, 600/573, 600/584, 210/634, 210/600, 210/645-646
• US Class Current: 600/366
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 1/1607 before use, i.e. upstream of dialyser
• CPC Class Codes: A61M 1/1609 after use, i.e. downstream of dialyser
• CPC Class Codes: A61M 1/1613 Profiling or modelling of patient or predicted treatment evolution or outcome
• CPC Class Codes: A61M 1/1617 using measurements made during a temporary variation of a characteristic of the fresh dialysis fluid
• CPC Class Codes: A61M 1/165 with a dialyser bypass on the dialysis fluid line
• CPC Class Codes: A61M 1/361 before treatment
• CPC Class Codes: A61M 1/3612 after treatment
• CPC Class Codes: A61M 2202/0498 Urea
• CPC Class Codes: A61M 2205/15 Detection of leaks

Abstract

Methods and apparatus for calculating a parameter of mass exchange of a solute fluid are disclosed including passing the solute in a predetermined volume of the fluid on one side of a semi-permeable membrane in a dialyzer, passing an exchange fluid on the other side of the semi-permeable membrane, obtaining a concentration curve by repeatedly measuring the concentration of a solute such as urea in the mass exchange fluid, fitting an approximate curve having a logarithm comprising a substantially straight line with at least a portion of a concentration curve, determining a parameter of the approximation curve, and calculating the mass of urea in the predetermined volume of fluid by the formula m=(Q_d×c_d)/P where P is the mass of the urea, Q_d is the flow rate of the exchange fluid, C_d is the concentration of the urea in the exchange fluid, and P is the parameter.

Claims

1. A method for calculating a parameter of the mass exchange of a solute in a fluid comprising:

passing said solute in a predetermined volume of said fluid on one side of a semi-permeable membrane in a mass exchange device,

passing an exchange fluid on the other side of said semi-permeable membrane,

obtaining a solute concentration curve by repeatedly measuring the concentration of said solute in said exchange fluid,

fitting an approximation curve having a logarithm comprising a substantially straight line with at least a portion of said concentration curve,

determining a parameter of said approximation curve, and

calculating the mass of said solute in said predetermined volume of said fluid by the formula m=(Q_d·

c_d)/P wherein

m comprises said mass of said solute,

Q_d comprises the flow rate of said exchange fluid,

c_d comprises the concentration of said solute in said exchange fluid, and

P comprises said parameter.

2. The method of claim 1 including determining the flow rate of said exchange fluid, integrating the product of said flow rate of said exchange fluid and said concentration of said solute in said exchange fluid over time in order to calculate the accumulated mass of said solute in said exchange fluid, and calculating a solute reduction index by the formula:

3. The method of claim 1 wherein said mass exchange device comprises a dialyzer, said mass exchange fluid comprises a dialysate fluid, and said solute comprises urea.

4. The method of claim 1 wherein said parameter corresponds to a whole body clearance divided by said predetermined volume of said fluid.

5. The method of claim 1 wherein said passing of said exchange fluid on said other side of said semi-permeable membrane comprises passing a finite initial concentration of said solute and wherein said measuring of said solute concentration comprises repeatedly measuring the difference of said solute concentration across said semi-permeable membrane.

6. The method of claim 1 wherein said fitting of said approximating curve comprises obtaining a compensated concentration by subtracting a predetermined concentration term from said concentration of said solute, obtaining the logarithm of said compensated concentration, and fitting a straight line to said logarithm of said compensated concentration, whereby said predetermined concentration term compensates for the generation of said solute.

7. The method of claim 1 wherein said parameter of said approximation curve comprises a slope of said substantially straight line.

8. The method of claim 1 wherein said fitting of said approximation curve excludes a predetermined initiation period.

9. The method of claim 8 wherein said predetermined initiation period comprises about 60 minutes.

10. The method of claim 1 including periodically interrupting said passing of said exchange fluid on said other side of said semi-permeable membrane for a first time period, and adjusting the time scale by replacing said first time period with a second time period, said second time period being less than said first time period.

11. The method of claim 1 wherein said parameter comprises a slope with respect to time in the following equation:

12. The method of claim 11 including determining the momentary mass by the equation:

13. The method of claim 12 including integrating said relative dialysis efficiency over time, whereby an estimate of the total dialysis dosage can be obtained.

14. The method of claim 12 wherein said fitting of said approximation curve comprises calculating a line passing through the greatest number of points in said logarithm of said concentration curve.

15. The method of claim 14 wherein said calculating is compensated.

16. The method of claim 14 including calculating said momentary mass from all values of said concentration of said solute in said exchange fluid from said substantially straight line within a predetermined time period, calculating a calculated initial mass from said momentary mass, and estimating the actual initial mass from said calculated initial mass.

17. The method of claim 16 wherein said estimating of said actual mass comprises determining the mean or median value of said calculated initial mass.

18. The method of claim 11 including determining the momentary mass of said solute in said exchange fluid by determining the actual concentration of said solute in said exchange fluid by a method selected from the group consisting of analyzing a blood sample and equilibrating said exchange fluid with blood and determining the distribution value of said solute.

19. The method of claim 1 including estimating the distribution volume of said fluid, and determining the concentration of said solute in said fluid by dividing said calculated mass by said distribution volume.

20. The method of claim 19 wherein said estimating of said distribution volume is carried out utilizing Watson'"'"'s formula.

21. The method of claim 1 including measuring the concentration of said solute in said fluid and determining the distribution volume of said solute in said fluid by dividing the calculated mass and said concentration of said solute in said fluid.

22. The method of claim 3 including introducing a disturbance into said dialyzer and measuring the resulting effect in said dialysate, whereby the concentration of said solute in said fluid is measured, calculating the effective clearance of said dialyzer from said measured resulting effect on said dialysate, calculating the plasma water concentration of said solute utilizing the formula

23. The method of claim 1 including determining a deviation of said concentration curve from said approximation curve, and emitting an alarm based upon said deviation with respect to a predetermined threshold level.

24. The method of claim 3 wherein said parameter comprises the slope of ln(c_d−

c_k) as a function of (V₀/UF)ln(V/V₀) in the equation;

25. The method of claim 24 comprising determining said momentary mass according to the equation:

32. The apparatus of claim 21 wherein said parameter comprises the slope of said substantially straight line.

33. The apparatus of claim 21 wherein said first calculation means includes means for excluding data obtained during said initiation period.

34. The apparatus of claim 33 wherein said initiation period comprises about 60 minutes.

26. Apparatus for calculating a parameter of a mass exchange procedure comprising:

mass exchange means for passing a solute in a predetermined volume of a fluid on one side of a semi-permeable membrane and passing a mass exchange fluid on the other side of said semi-permeable membrane in order to exchange said mass of said solute therebetween;

measuring means for measuring the concentration of said solute in said mass exchange fluid, whereby a solute concentration curve can be provided;

first calculation means for fitting an approximation curve having a logarithm comprising a substantially straight line to at least a portion of said solute concentration curve;

second calculation means for determining a parameter of said approximation curve; and

third calculation means for calculating the mass of said solute in said predetermined volume of said fluid by means of the formula

27. The apparatus of claim 26 including flow rate determination means for determining said flow rate of said mass exchange fluid,

fourth calculation means for calculating the accumulated mass of said solute in said mass exchange fluid from said mass exchange flow rate and said concentration of said solute by integrating the product of said mass exchange flow rate and said solute concentration in said mass exchange fluid over time, and

fifth calculation means for calculating a solute reduction index according to the formula:

28. The apparatus of claim 27 wherein said mass exchange means comprises a dialyzer, said exchanging of said solute between the sides of said semi-permeable membrane comprises dialysis, said mass exchange fluid comprises a dialysate fluid, and said solute comprises urea.

29. The apparatus of claim 28 including flow rate measuring means for measuring the flow rate of said dialysate, and wherein said third calculation means includes means for calculating the accumulated mass of said urea in said dialysate by integrating the product of said flow rate of said dialysate and the concentration of said solute in said dialysate fluid over time.

30. The apparatus of claim 28 wherein said dialysate fluid has an initial concentration of said urea which is greater than zero, and wherein said measuring means measures the concentration difference across said semi-permeable membrane.

31. The apparatus of claim 28 wherein said first calculation means includes means for subtracting a first compensation term comprising G/Q_d from said concentration of said urea in order to obtain a compensated concentration, whereby a straight line can be fitted to the logarithm of said compensated concentration so that said compensation term compensates for the production of said urea over time.

35. The apparatus of claim 28 wherein said first calculation means includes means for adjusting the time scale whereby when said flow of said dialysate fluid is interrupted for a first time period said first time period can be replaced with a second time period, said second time period being shorter than said first time period.

36. The apparatus of claim 28 wherein said parameter comprises the slope with respect to time, and wherein said second calculation means includes means for calculating said parameter by means of the following equation:

37. The apparatus of claim 36 wherein said second calculation means includes means for calculating a momentary mass according to the equation:

38. The apparatus of claim 37 wherein said second calculation means comprises means for integrating said relative dialysis efficiency over time whereby an estimate of the total dialysis dose is provided.

39. The apparatus of claim 26 wherein said second calculation means comprises means for fitting said approximation curve by calculating a line passing through the greatest number of points in the logarithm of said concentration curve.

40. The apparatus of claim 39 wherein said calculation means includes means for calculating the momentary mass of said solute using the values of said concentration of said solute in said mass exchange fluid within a predetermined limit from said substantially straight line which can then be used to calculate the initial mass of said solute, which can be used to estimate the actual initial mass of said solute.

41. The apparatus of claim 39 wherein said second calculation means further includes means for estimating said actual initial mass based upon the median or mean value of said initial mass.

42. The apparatus of claim 37 including means for determining a momentary mass of said solute by analyzing a blood sample or by equilibration of said dialysate with blood and determining the actual concentration of said solute and measuring the distribution volume of said solute.

43. The apparatus of claim 28 including means for estimating the distribution volume of said dialysate and for determining the concentration of said urea in said dialysate by dividing said calculated mass by said volume.

44. The apparatus of claim 43 wherein said means for estimating said distribution volume utilizes Watson'"'"'s formula.

45. The apparatus of claim 28 including means for measuring the concentration of said urea in said dialysate and for determining the distribution volume by dividing said calculated mass by said concentration.

46. The apparatus of claim 28 wherein said measuring means comprises means for introducing a disturbance into said dialyzer, means for measuring the resulting effect in said dialysate and for calculating the effective clearance of said dialyzer from said resulting measurements, means for calculating the plasma water concentration of said solute by the formula:

47. The apparatus of claim 28 including means for determining a deviation of said concentration curve from said approximation curve and alarm means for emitting an alarm upon deviation greater than a predetermined threshold level.

48. The apparatus of claim 28 wherein said parameter comprises a slope and wherein said second calculation means comprises means for calculating said slope in the equation:

49. The apparatus of claim 48 wherein said second calculation means includes means for calculating a momentary mass according to the equation: