Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Biological or biochemical
Reexamination Certificate
2000-12-01
2004-02-10
Allen, Marianne P. (Department: 1631)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Biological or biochemical
C435S004000, C324S071100, C210S739000
Reexamination Certificate
active
06691040
ABSTRACT:
The invention relates to a method for determining a parameter indicative of the progress of an extracorporeal blood treatment, in particular a purification treatment whose purpose is to alleviate renal insufficiency, such as haemodialysis or haemodiafiltration.
It will be recalled that haemodialysis consists in making a patient's blood and a treatment liquid approximately isotonic with blood flow, one on either side of the semipermeable membrane of a haemodialyser, so that, during the diffusive transfer which is established across the membrane in the case of substances having different concentrations on either side of the membrane, the impurities in the blood (urea, creatinine, etc.) migrate from the blood into the treatment liquid. The ion concentration of the treatment liquid is also generally chosen so as to correct the ion concentration of the patient's blood.
In treatment by haemodiafiltration, a convective transfer by ultrafiltration, resulting from a positive pressure difference created between the blood side and the treatment-liquid side of the membrane, is added to the diffusive transfer obtained by dialysis.
It is of the utmost interest to be able to determine, throughout a treatment session, one or more parameters indicative of the progress of the treatment so as to be able, where appropriate, to modify the treatment conditions that were fixed initially for the purpose of a defined therapeutic objective.
The parameters, the knowledge of which makes it possible to follow the progress of the treatment, i.e. also to assess the suitability of the initially fixed treatment conditions to the therapeutic objective, are, in particular, the concentration in the blood of a given solute (for example, sodium) or the actual dialysance D or the actual clearance K of the exchanger for such and such a solute (the dialysance D and the clearance K representing the purification efficiency of the exchanger) or the dialysis dose administered after a treatment time t, which, according to the work of Sargent and Gotch, may be likened to the dimensionless ratio Kt/V, where K is the actual clearance in the case of urea, t the elapsed treatment time and V the volume of distribution of urea, i.e. the total volume of water in the patient (Gotch F. A. and Sargent S. A., “A mechanistic analysis of the National Cooperative Dialysis Study (NCDS)”, Kidney Int. 1985, Vol. 28, pp. 526-34).
These parameters all have the same problem in respect of their determination, which is of requiring precise knowledge about a physical or chemical characteristic of the blood, whereas this characteristic cannot in practice be obtained by direct measurement on a specimen for therapeutic, prophylactic or financial reasons: firstly, it is out of the question to take, from a patient who is often anaemic, multiple specimens which would be necessary in order to monitor the effectiveness of the treatment during its execution; furthermore, given the risks associated with handling specimens of blood which may possibly be contaminated, the general tendency is to avoid such handling operations; finally, laboratory analysis of a specimen of blood is both expensive and relatively lengthy, this being incompatible with the desired objective.
Several methods have been proposed hitherto for determining in vivo haemodialysis parameters without having to take measurements on the blood.
Document EP 0,547,025 describes a method for determining the concentration of a substance, such as sodium, in a patient's blood subjected to a haemodialysis treatment. This method, which also makes it possible to determine the dialysance D—for example for sodium—of the haemodialyser used for administering the treatment, comprises the steps of:
making a first haemodialysis liquid and a second haemodialysis liquid having different sodium concentrations flow in succession through the haemodialyser;
measuring the conductivity of the first and second dialysis liquids, upstream and downstream of the haemodialyser; and
computing the concentration of sodium in the patient's blood (or the dialysance D of the haemodialyser for sodium) from the values of the conductivity of the liquid which are measured in the first and second dialysis liquids upstream and downstream of the haemodialyser.
Document EP 0,658,352 describes another method for the in vivo determination of the haemodialysis parameters, which comprises the steps of:
making at least a first and a second treatment liquid, having a characteristic (the conductivity, for example) associated with at least one of the parameters (the ion concentration of the blood, the dialysance D, the clearance K, Kt/V, for example) indicative of the treatment, flow in succession through the haemodialyser, the value of the characteristic in the first liquid upstream of the exchanger being different from the value of the characteristic in the second liquid upstream of the exchanger;
measuring, in each of the first and second treatment liquids, two values of the characteristic, respectively upstream and downstream of the exchanger;
making a third treatment liquid flow through the exchanger while the characteristic of the second liquid has not reached a stable value downstream of the exchanger, the value of the characteristic in the third liquid upstream of the exchanger being different from the value of the characteristic in the second liquid upstream of the exchanger;
measuring two values of the characteristic in the third liquid, respectively upstream and downstream of the exchanger; and
computing at least one value of at least one parameter indicative of the progress of the treatment from the measured values of the characteristic in the first, second and third treatment liquids.
Another method for the in vivo determination of the haemodialysis parameters which does not require taking measurements on the blood is described in document EP 0,920,877. This method includes the steps of:
making a treatment liquid flow through the exchanger, this treatment liquid having a characteristic which has an approximately constant nominal value upstream of the exchanger;
varying the value of the characteristic upstream of the exchanger and then re-establishing the characteristic to its nominal value upstream of the exchanger;
measuring and storing in memory a plurality of values adopted by the characteristic of the treatment liquid downstream of the exchanger in response to the variation in the value of this characteristic caused upstream of the exchanger;
determining the area of a downstream perturbation region bounded by a baseline and a curve representative of the variation with respect to time of the characteristic; and
computing the parameter indicative of the effectiveness of a treatment from the area of the downstream perturbation region and from the area of an upstream perturbation region bounded by a baseline and a curve representative of the variation with respect to time of the characteristic upstream of the exchanger.
All these methods have the common point of comprising a momentary modification of the value of a characteristic of the dialysis liquid (the conductivity, for example) and then the re-establishment of this characteristic to its initial value, which is generally the prescribed value. Even if the sequencing of the measurements is such that it takes less than two minutes to determine the desired parameter (the situation in the second method mentioned), it remains the case that all these methods can be carried out in practice only six times per hour.
One objective of the invention is to propose a method for determining a parameter indicative of the progress of an extracorporeal blood treatment which is virtually continuous, reliable and having no influence on the treatment carried out.
In order to achieve this objective, a method is provided for continuously determining a parameter (D, Cbin, K, Kt/V) indicative of the effectiveness 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 of a membr
Bosetto Antonio
Paolini Francesco
Finnegan Henderson Farabow Garrett & Dunner LLP
Hospal AG
Mahatan Channing S.
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