Method and a device for determining the dry weight of a patient with kidney failure

• US 20040064063A1
• Filed: 11/07/2003
• Published: 04/01/2004
• Est. Priority Date: 11/06/2000
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Deutschland GmbH (Fresenius Medical Care AG)
• Original Assignee: Fresenius Medical Care Deutschland GmbH (Fresenius Medical Care AG)
• Inventors: Chamney, Paul
• Granted Patent: US 7,072,710 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0535 Impedance plethysmography for measuring blood flow A61B5/0295
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/4869 Determining body composition
• CPC Class Codes: A61M 1/16 with membranes
• CPC Class Codes: A61M 2205/3393 by weighing the reservoir
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient

Abstract

The invention relates to a method and a device for monitoring the fluid status of a patient with kidney failure. In case of renal failure all forms of ingested fluid accumulate in body tissues causing increased stress on the circulatory system. This surplus fluid has to be removed during a dialysis treatment by ultrafiltration of the blood. The amount of this surplus fluid or the weight corrected for this surplus fluid, i.e. the dry weight, is an important parameter for managing the fluid status of a dialysis patient. According to the invention the dry weight Wgt_dry(t) of a patient at a time t is determined by determining the extracellular water volume ECV(t) of the patient at the time t, by determining the weight Wgt(t) of the patient at the time t and by deriving the dry weight Wgt_dry(t) of the patient from an intersection of a function derived from the determined ECV(t) and Wgt(t) values with a previously established extracellular water volume (ECV) against dry weight (Wgt_dry) reference relation representing healthy subjects. To obtain more accurate results it is also proposed to take into account a compartimental mass correction Δm(t). The invention also relates to a device for deriving the dry weight Wgt_dry(t).

Claims

1. A method for determining the dry weight Wgt_dry(t) of a patient at a time t comprising the steps of:

determining the extracellular water volume ECV(t) of the patient at the time t,

determining the weight Wgt(t) of the patient at the time t,

deriving the dry weight Wgt_dry(t) of the patient from an intersection of a function derived from the determined ECV(t) and Wgt(t) values with a previously established extracellular water volume (ECV) against dry weight (Wgt_dry) reference relation representing healthy subjects.

2. The method according to claim 1 characterized in that ECV(t) is derived from a bioimpedance measurement.

3. The method according to claim 2 characterized in that the bioimpedance measurement is a whole body measurement.

4. The method according to claim 2 characterized in that the bioimpedance measurement is a segmental measurement.

5. The method according to any of the preceding claims characterized in that Wgt_dry(t) is determined using the following expression:

6. The method according to any of the preceding claims characterized in that the ECV(t_i) and Wgt(t_i) values of a patient at times t_j, i=1 . . . j, are stored and that the dry body weight Wgt_dry(t_j) is derived by a linear regression analysis.

7. The method according to any of the preceding claims characterized in that a compartimental mass correction Δ

m(t) is determined in order to derive the dry body weight Wgt_dry(t) from the determined weight Wgt(t).

8. The method according to claim 7 characterized in that the dry weight Wgt_dry(t) is derived by the following expression:

9. The method according to claims 7 or 8 characterized in that the compartimental mass correction Δ

m(t) encompasses a fat mass correction Δ

f(t) and/or a muscle mass correction Δ

m_muscle(t).

10. The method according to any of the claim 7 or 8 characterized in that the intracellular water volume ICV(t) is determined for the patient at the time t and that the determined ICV(t) is used to derive the compartimental mass correction Δ

m(t).

11. The method according to claim 1 characterized in that the method for determining the dry weight Wgt_dry(t) of a patient at a time t further comprises the steps of determining the intracellular water volume ICV(t) of the patient at the time t and of deriving the dry weight Wgt_dry(t) of the patient also from an intersection of a function derived from the determined ICV(t) and Wgt(t) values with a previously established intracellular water volume (ICV) against Wgt_dry reference relation representing healthy subjects.

12. A device (10) for carrying out the method according to any of the preceding claims comprising

a microprocessor unit (1) which in turn comprises a microprocessor program storage unit (1a),

a input unit (2) to enable entering the values of ECV(t) and Wgt(t),

a computer storage unit (3) for storing the ECV(t) and Wgt(t) values,

wherein the microprocessor program storage unit (1a) comprises a program for deriving the dry weight Wgt_dry(t) from an intersection (IS) of a function derived from the stored ECV(t) and Wgt(t) values with a previously established ECV against Wgt_dry reference relation representing healthy subjects.

13. The device according to claim 12 characterized in that it further comprises means (5) for determining the ECV(t) value.

14. The device according to claims 12 or 13 characterized in that it further comprises means (7) for determining the Wgt(t) value.

15. The device according to claim 13 characterized in that the means (5) for determining the ECV(t) value is a bioimpedance measurement device.

16. The device according to claim 12 characterized in that the input unit (2) is a manual user interface, preferably a keyboard.

17. The device according to any of the claims 12 to 16 characterized in that the input unit (2) comprises an interface to the means (5) for determining the ECV(t) value and/or the means (7) for determining the Wgt(t) value.

18. The device according to any of the claims 12 to 17 characterized in that the program for deriving the dry body weight Wgt_dry(t) uses the following expression:

19. The device according to any of the claims 12 to 18 characterized in that the computer storage unit (3) is capable of storing the ECV(t_i) and Wgt(t_i) values of a patient at times t_i, i=1 . . . j, and that the program for deriving the dry weight Wgt_dry(t_j) uses a linear regression analysis.

20. The device according to any of the claims 12 to 19 further comprising an output unit (9) that is linked to the microprocessor unit for outputting, preferably displaying the derived Wgt_dry(t) value.

21. The device according to any of the claims 12 to 20 characterized in that the program stored in the microprocessor program storage unit (1a) is suitable to determine a compartimental mass correction Δ

m(t) in order to derive the dry body weight Wgt_dry(t) from the determined weight Wgt(t).

22. The device according to claim 21 characterized in that the program for deriving the dry body weight Wgt_dry(t) uses the following expression:

23. The device according to any of the claims 21 or 22 characterized in that the input unit (2) is also suitable to enable entering a value for the intracellular water volume ICV(t) of the patient at the time t, the computer storage unit (3) is able to store the ICV(t) value and that the program for deriving the dry body weight Wgt_dry(t) uses the ICV(t) value in order to determine the compartimental mass correction Δ

m(t).

24. The device according to claims 23 characterized in that the device further comprises means for determining the ICV(t) value, preferably a bioimpedance device.

25. The device according to claim 12 characterized in that input unit (2) is also suitable to enable entering a value for the intracellular water volume ICV(t) of the patient at the time t, the computer storage unit (3) is able to store the ICV(t) value and that the program for deriving the dry weight Wgt_dry(t) of a patient at a time t further comprises a part to derive the dry weight Wgt_dry(t) also from an intersection of a function derived from the determined ICV(t) and Wgt(t) values with a previously established intracellular water volume (ICV) against Wgt_dry reference relation representing healthy subjects.