Method for determining a parameter indicative of the progress of an extracorporeal blood treatment

• US 20010004523A1
• Filed: 12/01/2000
• Published: 06/21/2001
• Est. Priority Date: 12/02/1999
• Status: Active Grant

• Current Assignee: Baxter Healthcare SA (Baxter International Inc.)
• Original Assignee: Gambro Hospal Schweiz AG (Baxter International Inc.)
• Inventors: Paolini, Francesco, Bosetto, Antonio
• Granted Patent: US 6,691,040 B2
• Time in Patent Office: Days
• US Class Current: 435/4
• 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 2205/3317 Electromagnetic, inductive or dielectric measuring means
• CPC Class Codes: A61M 2205/3324 PH measuring means
• CPC Class Codes: A61M 2205/52 with memories providing a history of measured variating parameters of apparatus or patient

Abstract

A method for continuously determining a parameter (D, Cbin, K, Kt/V) indicative of an extracorporeal blood treatment includes flowing patient'"'"'s blood and a treatment liquid flow on opposite sides of a semipermeable membrane. The treatment liquid has a characteristic (Cd) associated with the effectiveness of the treatment flow through the exchanger. A succession of variations are caused in the characteristic (Cd) upstream of the exchanger, and a plurality of values (Cdin1 . . . Cdinj . . . Cdinp) of the characteristic (Cd) upstream of the exchanger are continuously stored in memory. Similarly, plurality of values (Cdout1 . . . Cdoutj . . . Cdoutp) adopted by the characteristic (Cd) downstream of the exchanger are continuously stored in memory. From the stored values, the effectiveness of the treatment is calculated using a mathematical model.

Claims

1. Method for continuously determining a parameter (D, Cbin, K, Kt/V) indicative of an extracorporeal blood treatment, consisting in making a patient'"'"'s blood and a treatment liquid flow, one on either side of the semipermeable membrane (4) of a membrane exchanger (1), this method comprising the steps:

making a treatment liquid having a characteristic (Cd) associated with the effectiveness of the treatment flow through the exchanger (1);

causing a succession of variations in the characteristic (Cd) upstream of the exchanger (1);

continuously storing in memory a plurality of values (Cdin1 . . . Cdinj . . . Cdinp) of the characteristic (Cd) upstream of the exchanger (1);

measuring and continuously storing in memory a plurality of values (Cdout1 . . . Cdoutj . . . Cdoutp) adopted by the characteristic (Cd) downstream of the exchanger (1) in response to the variations in the characteristic (Cd) which are caused upstream of the exchanger (1);

computing, each time that a predetermined number of new values (Cdoutj) of the characteristic (Cd) downstream of the exchanger has been stored, a parameter (D, Cbin, K, Kt/V) indicative of the effectiveness of the extracorporeal blood treatment, from a first series of values (Cdinj) of the characteristic (Cd) downstream of the exchanger (1), and by means of a mathematical model of the influence of the characteristic (Cd) on the effectiveness of the treatment, the mathematical model having at least one coefficient consisting of a parameter (D, Cbin) indicative of the effectiveness of the extracorporeal blood treatment.

2. Method according to

claim 1

, characterized in that the computation step consists in computing the parameter (D, Cbin, K, Kt/v) indicative of the effectiveness of the extracorporeal blood treatment each time that a new value (Cdoutj) of the characteristic (Cd) downstream of the exchanger (1) has been stored.

3. Method according to either of claims 1 and 2, characterized in that the second series of values (Cdoutj) of the characteristic (Cd) downstream of the exchanger (1) comprises the last value stored in memory.

4. Method according to one of

claims 1

to

3

, characterized in that the second series of values (Cdoutj) of the characteristic (Cd) downstream of the exchanger (1) comprises a predetermined number of successive values.

5. Method according to

claim 1

, characterized in that it furthermore includes the step of establishing a correspondence between each value (Cdoutj+z) of the second series of values and a value (Cdinj) of the first series of values, the value (Cdoutj+z) of the second series of values being shifted over time with respect to the corresponding value (Cdinj) of the first series of values by a hydraulic delay (T) equal to the time taken by a liquid specimen to flow through a treatment liquid circuit (9, 10) connected to the exchanger (1), between a point lying upstream of the exchanger (1) and a point lying downstream of the exchanger (1).

6. Method according to

claim 5

, characterized in that it furthermore includes the step of determining the value of the hydraulic delay (T).

7. Method according to

claim 6

, characterized in that the hydraulic delay (T) is one of the coefficients of the mathematical model and in that the step of determining the value of the hydraulic delay (T) comprises the steps of:

computing, by means of the mathematical model, for each value (Cdinj) of the first series of values, a corresponding value (Cd*outj+z) of the characteristic (Cd) downstream of the exchanger (1); and

determining the optimum value of the hydraulic delay (T) for which the correspondence between the computed values (Cd*outj+z) of the characteristic (Cd) downstream of the exchanger (1) and the corresponding measured values (Cdoutj+z) of the characteristic (Cd) downstream of the exchanger (1) is the most precise.

8. Method according to one of

claims 5

to

7

, characterized in that the step of computing a parameter (D, Cbin) indicative of the effectiveness of the extracorporeal blood treatment comprises the steps of:

computing, by means of the mathematical model, for each value (Cdinj) of the first series of values, a corresponding value (Cd*outj+z) of the characteristic (Cd) downstream of the exchanger (1); and

determining the optimum value of the parameter (D, Cbin) for which the correspondence between the computed values (Cd*outj+z) of the characteristic (Cd) downstream of the exchanger (1) and the corresponding measured values (Cdoutj+z) of the characteristic (Cd) downstream of the exchanger (1) is the most precise.

9. Method according to

claim 8

, characterized in that the mathematical model is linear and in that the step of determining the optimum value of the parameter (D, Cbin) consists in determining that value of the parameter (D, Cbin) for which the sum of the squares of the differences between the measured values (Cdoutj+z) and the corresponding computed values (Cd*outj+z) of the characteristic (Cd) downstream of the exchanger is the least.

10. Method according to one of

claims 1

to

9

, characterized in that the step of varying the characteristic (Cd) upstream of the exchanger (1) comprises the step of adjusting the characteristic (Cd) as a function of the variation of a parameter of a device intended for implementing the treatment and/or of a parameter of the patient, so that this parameter remains within a range of permissible values.

11. Method according to

claim 10

, characterized in that the parameter of the patient is the relative variation in the blood volume of the patient.

12. Method according to one of

claims 1

to

9

, characterized in that the step of varying the characteristic (Cd) upstream of the exchanger (1) comprises the step of storing in memory, before the treatment, a rule of variation of the characteristic upstream of the exchanger.

13. Method according to

claim 12

, characterized in that the rule of variation entails the regular alternation of an increase and of a decrease in the characteristic (Cd) of a defined amount.

14. Method according to one of

claims 1

to

9

, characterized in that it furthermore includes the step of preparing the treatment liquid, and in that the step of varying the characteristic (Cd) upstream of the exchanger (1) is inherent in the perturbations associated with the preparation of the treatment liquid.

15. Method according to one of

claims 1

to

14

, characterized in that it furthermore includes the step of measuring the values (Cdinj) of the characteristic (Cd) upstream of the exchanger (1).

16. Method according to one of

claims 1

to

15

, characterized in that the characteristic of the treatment liquid associated with the effectiveness of the treatment is a characteristic (Cd) of the treatment liquid associated with the exchanges across the membrane of the exchanger (1) and in that the mathematical model of the influence of the characteristic (Cd) on the effectiveness of the treatment is a mathematical model of the exchanges across the membrane of the exchanger (1).

17. Method according to

claim 16

, characterized in that the characteristic (Cd) of the treatment liquid is associated with ion and solute exchanges or with heat exchanges across the membrane of the exchanger (1).

18. Method according to

claim 17

, characterized in that the parameter indicative of the effectiveness of an extracorporeal blood treatment is the dialysance (D) and in that the mathematical model is defined by the following equations:

Cdoutj+z+1=a×

Cdoutj+z+b×

Cdinj+c$\mathrm{Ø<br><br>}=-\frac{\mathrm{Ts}}{\ln <br><br>\left(a\right)}$$\mathrm{Dr}=1-\frac{b}{1-{\mathrm{<br><br>}}^{-\mathrm{Ts}/\mathrm{Ø<br><br>}}}$$\mathrm{Cbin}=\frac{C}{\mathrm{Dr}\times <br><br>\left(1-{\mathrm{<br><br>}}^{-\mathrm{Ts}/\mathrm{Ø<br><br>}}\right)}$

in which;

Cdinj is the sodium concentration in the treatment liquid, upstream of the exchanger (1);

Cdoutj is the sodium concentration in the treatment liquid, downstream of the exchanger (1);

Ts is the sampling period;

Ø

is the time constant;

Dr=D/Qd is the relative dialysance, Qd being the treatment liquid flow rate and D being the dialysance.

19. Method according to

claim 17

, characterized in that the variation imposed on the characteristic (Cd) of the treatment liquid is periodic and in that it consists in computing the amplitude |Cdin| of the variation in the conductivity upstream of the exchanger (1) from the first series of values (Cdinj) and the amplitude |Cdout| of the variation in the conductivity downstream of the exchanger (1) from the second series of values (Cdoutj).

20. Method according to

claim 19

, characterized in that the parameter indicative of the effectiveness of an extracorporeal blood treatment is the dialysance (D) and in that the mathematical model is defined by the following equation:

$\mathrm{Dr}=\frac{D}{\mathrm{Qd}}=1-\frac{<br><br>\mathrm{Cdout}<br><br>}{<br><br>\mathrm{Cdin}<br><br>}$

in which Qd is the flow rate of the treatment liquid.

21. Method according to

claim 20

, characterized in that it furthermore consists in computing the average conductivity CdinM upstream of the exchanger (1) from the first series of values (Cdinj) and the average conductivity CdoutM downstream of the exchanger (1) from the second series of values (Cdoutj).

22. Method according to

claim 21

, characterized in that the parameter indicative of the effectiveness of an extracorporeal blood treatment is the ion concentration Cbin of the blood upstream of the exchanger (1) and in that the mathematical model is defined by the following equation:

$C<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{bin}=\frac{1}{\mathrm{Dr}}\times <br><br>\mathrm{CdoutM}-\frac{\left(1-\mathrm{Dr}\right)}{\mathrm{Dr}}\times <br><br>\mathrm{CdinM}$