Point of care heparin determination system

• US 20060016701A1
• Filed: 05/11/2005
• Published: 01/26/2006
• Est. Priority Date: 05/17/2004
• Status: Active Grant

• Current Assignee: Medtronic Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Incorporated (Medtronic Plc)
• Inventors: Meyer, Randy, Hobot, Christopher, Ramamurthy, Narayanan, Cheek, Daniel S., Nippoldt, Douglas Dean, Qin, Wei, Ye, Qingshan (Sam), Sitko, Vitally G., Bonnema, Kelvin
• Granted Patent: US 7,699,966 B2
• Time in Patent Office: Days
• US Class Current: 205/792
• CPC Class Codes: A61M 1/3675 Deactivation
• CPC Class Codes: G01N 27/333 Ion-selective electrodes or membranes glass electrodes G01N27/36
• CPC Class Codes: G01N 27/3335 the membrane containing at least one organic component G01N27/3271 takes precedence; aspects concerning the enzyme reagent in enzyme electrodes C12Q1/001
• CPC Class Codes: G01N 33/86 involving blood coagulating time or factors, or their receptors

Abstract

Methods and devices for point of care determination of heparin concentration in blood are described. Cartridges including protamine ion sensitive electrodes (ISEs) and reference electrodes and systems for automatically determining heparin concentration in the cartridges are provided. Some systems add blood to a protamine bolus sufficient to bind all heparin, leaving excess protamine. The excess protamine concentration can be determined by measuring the initial slope of the electrode potential rate of change, and comparing the slope to known protamine concentration slope values In some cartridges, an oscillating pressure source moves the blood-protamine mixture back and forth across the protamine ISE. Some systems also use a second blood sample having the heparin removed or degraded to create a blank reference sample. Protamine ISEs can include polyurethane polymer, DNNS ionophore, and NPOE plasticizer. The polyurethane may include hard segments and soft segments, where both hard and soft segments may include cyclic and straight chain aliphatic moieties having essentially no ester or ether groups. Some hard segments may include methylene diphenyl groups. Some reference electrodes have the same polymer, plasticizer, and ionophore as the measurement electrode, but with a different concentration of ionophore.

Claims

1. A system for determining heparin concentration in a sample, the system comprising:

a cartridge including a fluid path, and sample port in fluid communication with the fluid path; and

a protamine Ion Selective Electrode (ISE) pair in fluid communication with the fluid path; and

a known amount of protamine disposed in fluid communication with the fluid path.

2. The system of claim 1, further comprising:

means for oscillating pressure in the fluid channel.

3. The system of claim 1, further comprising:

means for determining a first rate of change of the protamine ISE pair output signal.

4. The system of claim 3, further comprising:

means for calculating the heparin concentration in the sample at least in part as a function of the protamine ISE pair output rate of change over time.

5. The system of claim 4, in which the means for calculating the heparin concentration includes determining a rate of an initial change with respect to time of the protamine ISE pair prior to about 2 minutes of adding the sample to the cartridge.

6. The system of claim 1, further comprising a pressure port in fluid communication with the fluid path.

7. The system of claim 6, in which the pressure port and sample port are disposed on opposite sides of the fluid path relative to the protamine Ion Selective Electrode (ISE) pair.

8. The system of claim 6, in which the pressure port and sample port are disposed on the same side of the fluid path relative to the protamine Ion Selective Electrode (ISE) pair.

9. The system of claim 8, in which the fluid path includes a compressible fluid in a fluid path region on an opposite of the protamine Ion Selective Electrode (ISE) pair from the pressure port.

10. The system of claim 6, in which the protamine Ion Selective Electrode (ISE) pair is disposed between the pressure port and a closed portion of the fluid path which contains a compressible fluid, such that applying pressure to the pressure port compresses the compressible fluid and moves the sample across the ISE.

11. The system of claim 1, further comprising an oscillating pressure source operably coupled to the fluid path.

12. The system of claim 11, in which the oscillating pressure source is mechanical.

13. The system of claim 11, in which the oscillating pressure source is electro-mechanical.

14. The system of claim 11, in which the oscillating pressure source is pneumatic.

15. The system of claim 1, further comprising an amount of citrate disposed in fluid communication with the fluid path.

16. A method for determining an initial heparin concentration in a sample, the method comprising:

adding an amount of protamine to the sample sufficient to bind all the heparin in the sample;

determining a remaining protamine concentration in the sample using a protamine ion-selective electrode pair; and

calculating the initial heparin concentration in the sample using the remaining protamine concentration.

17. The method of claim 16, in which the step of determining a remaining protamine concentration includes the step of monitoring a change over time in a signal from the protamine ion-selective electrode pair.

18. The method of claim 16, in which the determining remaining protamine includes monitoring a change over time in a signal from the protamine ion-selective electrode pair and using an initial slope of the protamine ion-selective electrode pair signal change over time.

19. The method of claim 18, in which the determining the protamine concentration includes using a set of initial slopes obtained in a similar method for known heparin concentration samples.

20. The method of claim 16, in which the determining remaining protamine includes monitoring a change with respect to time in a signal from the protamine ion-selective electrode pair;

determining the time of maximum rate of change of the protamine ion-selective electrode pair signal change with respect to time; and

determining the protamine concentration as a function of the determined time using a set of times obtained in a similar method for known heparin concentration samples.

21. The method of claim 16, in which the determining remaining protamine includes monitoring a change with respect to time in a signal from the protamine ion-selective electrode pair;

determining a maximum rate of change of the protamine ion-selective electrode pair signal; and

determining the protamine concentration as a function of the determined maximum rate of change using a set of maximum rate of change of the differential potential obtained using a similar method for known heparin concentration samples.

22. The method of claim 16, in which the dried protamine was pre-loaded in a cartridge used in the measuring.

23. A method for determining protamine concentration, the method comprising exposing a protamine ion sensitive electrode to a sample containing an unknown protamine concentration;

exposing a reference electrode to the sample;

tracking the differential electrical potential between the protamine ion selective electrode and the reference electrode over time;

determining the protamine concentration at least in part as a function of the differential electrical potential between the protamine ion selective electrode and the reference electrode over time.

24. The method of claim 23, in which the protamine ion selective electrode includes a polymer, a plasticizer, and an ionophore comprising DNNS and/or derivatives thereof.

25. The method of claim 24, in which the determining the protamine concentration includes determining the time of maximum rate of change of the differential potential with respect to time;

and

determining the protamine concentration as a function of the determined time using a set of times obtained in a similar method for known protamine concentration samples.

26. The method of claim 23, in which the step of determining the protamine concentration includes the steps of:

determining the maximum rate of change of the differential potential; and

determining the protamine concentration as a function of the determined maximum rate of change of the differential potential using a set of maximum rate of change of the differential potential obtained using a similar method for known protamine concentration samples.

27. The method of claim 23, in which the determining the protamine concentration includes determining the an initial slope of the rate of change of the differential potential;

and

determining the protamine concentration as a function of the determined initial slope using a set of initial slopes of the differential potential obtained using a similar method for known protamine concentration samples.

28. The method of claim 23, in which the determining the protamine concentration includes

determining the a rate of change of the differential potential in a time window within about 2 minutes of the exposure;

and

determining the protamine concentration as a function of the determined rate of change using a set of rate of changes of the differential potential obtained using a similar method for known protamine concentration samples.

29. A polyion selective electrode pair comprising:

a first electrode including a first polymer, a plasticizer, and an ionophore for binding to the polyion, the ionophore present in a first, non-negligible concentration; and

a second electrode including the first polymer and the plasticizer.

30. The polyion selective electrode pair of claim 29, in which the polyion selective electrode pair is not self-plasticizing, in which the plasticizer comprises predominantly of a plasticizing substance added to the polymer.

31. The polyion selective electrode pair of claim 29, in which the plasticizer is predominantly at least one compound not covalently bonded to the polymer.

32. The polyion selective electrode pair of claim 29, in which the second electrode further comprises the ionophore present in a second concentration that is substantially higher than the first ionophore concentration.

33. The polyion selective electrode pair of claim 29, wherein the ionophore is an ionophore for transporting protamine within the polymer.

34. The polyion selective electrode pair of claim 33, wherein the ionophore includes DNNS.

35. The polyion selective electrode pair of claim 33, wherein the ionophore includes DNNS or derivatives thereof, and/or combinations thereof.

36. The polyion selective electrode pair of claim 31, wherein the plasticizer includes NPOE.

37. A method using the polyion selective electrode of claim 29 for determining the polyion concentration in a solution, the method comprising:

exposing the first electrode to the solution;

exposing the second electrode to the solution; and

determining the polyion concentration as a function of an electrical potential between the first electrode and the second electrode.

38. The method of claim 37, in which the polyion includes protamine and in which the ionophore transports protamine into the polymer.

39. The method of claim 38, in which the ionophore includes DNNS.

40. A method for measuring heparin in a first blood sample, the method comprising:

inactivating essentially all the heparin in the first blood sample to create a reference sample;

measuring the output of a first ion selective electrode pair exposed to the reference sample, the first electrode pair having a protamine ion selective electrode and a reference electrode;

measuring the output of a second ion selective electrode pair exposed to a second blood sample, the second electrode pair having a protamine ion selective electrode and a reference electrode; and

determining the second sample heparin amount including using the second electrode pair output adjusted by the first electrode pair output.

41. The method of claim 40, in which the first and second blood samples derive from a common blood sample.

42. The method of claim 41, in which the first blood sample is taken from a patient at a first point in time and the second blood sample is taken from the same patient at a second point in time subsequent to the first point in time.

43. The method of claim 41, in which the first and second electrode pairs measuring occurs substantially contemporaneously with each other.

44. The method of claim 41, in which the second electrode pair measuring occurs subsequent to the first electrode pair measuring.

45. The method of claim 44, further comprising measuring a third blood sample from the same patient using a third electrode pair.

46. The method of claim 40, in which the inactivating includes degrading the heparin using an enzyme.

47. The method of claim 40, in which the inactivating includes binding the heparin.

48. The method of claim 40, in which the inactivating includes binding the heparin to polycations immobilized on to a solid matrix.

49. The method of claim 40, in which the inactivating includes binding the heparin to polylysine immobilized on a solid matrix.

50. A heparin concentration determination system comprising:

a first sample chamber having a first protamine ISE pair and a first means for mixing;

a second sample chamber having a second protamine ISE pair and a second means for mixing;

a first sample delivery channel for delivering a first sample into the first sample chamber;

a second sample delivery channel for delivering a second sample into the second sample chamber; and

a heparin remover in communication with the first delivery channel for binding, degrading, and/or inactivation heparin entering the first sample chamber.

51. The system of claim 50, wherein the first and second channels derive from a common sample delivery channel.

52. The system of claim 50, in which the first and second chambers each include a punctureable seal, wherein the first and second delivery channels are formed by puncturing the seals.

53. A method for determining a heparin concentration in a sample, the method comprising:

adding the sample and a protamine amount sufficient to bind all the heparin expected in the sample to a sample chamber to mix the sample and protamine;

obtaining a differential electrical potential between a reference electrode and a protamine sensitive electrode over time, where the electrode are in contact with the mixed sample; and

determining the heparin concentration at least in part as a function of the slope of the differential electrical potential over time in a substantially linear region of electrical potential versus time.

54. The method of claim 53, in which the log of the slopes of various different protamine concentrations versus heparin concentration is substantially linear.

55. The method of claim 53, further comprising obtaining calibration values to use in the determining the heparin concentration by exposing a known protamine concentration solution to a similar, second reference and protamine sensitive electrode pair and obtaining the differential electrical potential over time for the second reference and protamine sensitive electrode pair.

56. A protamine sensitive electrode comprising:

a protamine transporting ionophore and a polymer including a segmented polyurethane, the polyurethane comprising;

alternating harder and softer segments, linked by urethane groups;

wherein the softer segments comprise a polyurethane having the general repeating formula—

(R₁—

U—

R₂—

U)_m—

,

wherein R₁ signifies a backbone comprising a first hydrocarbon chain having j carbon atoms and bonded to a cyclic aliphatic hydrocarbon ring bonded to a second hydrocarbon chain having k carbon atoms, wherein j and k are between about 4 and 12, wherein U signifies a urethane group, and

wherein R₂ signifies a hydrocarbon moiety essentially free of ether and ester groups and having a molecular weight of less than about 1000, and

wherein the average value of m is 1 or greater,

wherein the harder segments comprise a polyurethane having the general repeating formula —

(R₃—

U—

R₄—

U)_n—

, wherein R₃ and R₄ signify hydrocarbon moieties essentially free of ether and ester groups,

wherein R₃ is selected from the group consisting of aliphatic straight chain hydrocarbons, aliphatic branched hydrocarbons, and aliphatic cyclic hydrocarbons, in which a hard segment may have one, two, or more different members selected from the group consisting of aliphatic straight chain hydrocarbons, aliphatic branched hydrocarbons, and aliphatic cyclic hydrocarbons,

wherein R₄ includes at least one aromatic group in the backbone,

wherein where U signifies a urethane group, and

wherein the average value of n is 1 or greater.

57. The protamine sensitive electrode of claim 56, in which the R₁ first hydrocarbon chain and second hydrocarbon chain has a chain length of between about 8 and 10.

58. The protamine sensitive electrode of claim 57, in which the R₁ cyclic aliphatic ring has 6 carbons and includes a first pendant hydrocarbon at the 2 position and having a chain length of between about 2 and 6 and includes a second pendant hydrocarbon at the 3 position and having a chain length of between about 2 and 6.

59. The protamine sensitive electrode of claim 56, in which the hard segment R₃ in some instances signifies a backbone comprising a first hydrocarbon chain having j carbon atoms and bonded to a cyclic aliphatic hydrocarbon ring bonded to a second hydrocarbon chain having k carbon atoms, wherein j and k are between about 4 and 12, wherein U signifies a urethane group, and wherein the hard segment R₃ in other instances in the hard segment signifies a straight chain hydrocarbon having a chain length of between about 2 and 6.

60. The protamine sensitive electrode of claim 56, in which the hard segment R₄ includes methylene diphenyl.

61. The protamine sensitive electrode of claim 56, in which the soft segment R₁ is a 1-decyl-4-nonyl cyclohexyl group, and in which the R₂ is a straight chain hydrocarbon having a chain length of between about 2 and 6.

62. The protamine sensitive electrode of claim 61, in which the soft segment R₁ 1-decyl-4-nonyl cyclohexyl group has a pendent hydrocarbon chain at the 2 and/or 3 position having a chain length of between about 4 and 6.

63. The protamine sensitive electrode of claim 56, in which the hard segment R₃ is a 1-decyl-4-nonyl cyclohexyl group in some instances of the hard segment.

64. The protamine sensitive electrode of claim 56, further comprising a plasticizer.

65. The protamine sensitive electrode of claim 64 in which the polymer is self plasticizing, in which the plasticizer includes plasticizing groups bonded to the polymer.

66. The protamine sensitive electrode of claim 64, in which the plasticizer includes 2-nitroohenyloctyl ether (NPOE).

67. The protamine sensitive electrode of claim 56, further comprising pellethane 80A.

68. The protamine sensitive electrode of claim 56, further comprising a co-polymer formed of the hard and soft segments and pellethane 80A.

69. The protamine sensitive electrode of claim 56, in which the ionophore includes dinonylnapthalenesulfonate (DNNS).