Method and device for determining a blood constituent

Patent metadata

Field	Value
Publication number	US-9814412-B2
Application number	US-201213685198-A
Country	US
Kind code	B2
Filing date	Nov 26, 2012
Priority date	Dec 1, 2011
Publication date	Nov 14, 2017
Grant date	Nov 14, 2017

Abstract

A method and device for determining the concentration of blood constituents, in particular haemoglobin, in a hose line of an extracorporeal blood circuit of an extracorporeal blood treatment apparatus, and an extracorporeal blood treatment apparatus with a device for determining the concentration of a blood constituent, are based on the correction of the influence of the blood flow rate of the blood flowing through the hose line on the determination of the concentration of the blood constituent. The device comprises a computing and evaluation unit configured such that a correction factor is ascertained for the influence of the blood flow rate on the determination of the concentration of the blood constituent. The concentration of the blood constituent is then determined based on a relationship describing the dependence of the concentration of the blood constituent on the intensity of the decoupled electromagnetic radiation, taking account of the correction factor.

First claim

What is claimed is:

1. A method for determining a concentration of a blood constituent during an extracorporeal blood treatment performed by an extracorporeal blood treatment apparatus including a central control and computing unit that performs control and computing operations of the extracorporeal blood treatment apparatus, wherein blood flows through an arterial hose line into a blood chamber and via a venous hose line out of the blood chamber of a dialyser divided by a semipermeable membrane into the blood chamber and a dialysing fluid chamber, the method comprising:
calibrating, prior to use in the extracorporeal blood treatment, a measuring arrangement using a calibration blood flow rate;
storing the calibration blood flow rate in a memory of a computing and evaluation unit;
determining, via the central control and computing unit, a current blood flow rate;
storing the current blood flow rate in the memory of the computing and evaluation unit;
setting a preset threshold value for the difference between the current blood flow rate and the calibration blood flow rate;
storing the preset threshold value in the memory of the computing and evaluation unit;
coupling, via an emitter device of the measuring arrangement, electromagnetic radiation through the arterial hose line or the venous hose line into the blood;
measuring, via a detector of the measuring arrangement, the electromagnetic radiation decoupled through the arterial hose line or the venous hose line from the blood;
ascertaining, via the computing and evaluation unit, a correction factor to correct for an influence of the blood flow rate on a determination of the concentration of the blood constituent wherein the correction factor is ascertained only if a deviation between the current blood flow rate and the calibration blood flow rate is greater than the preset threshold value as determined by the computing and evaluation unit;
determining, via a determining device, the concentration of the blood constituent based on (a) a relationship describing a dependence of the concentration of the blood constituent on a measured intensity of the decoupled electromagnetic radiation, and (b) the correction factor; and
transmitting the concentration of the blood constituent from the determining device to the central control and computing unit of the extracorporeal blood treatment apparatus.

2. The method according to claim 1 , wherein the relationship describing the dependence of the concentration of the blood constituent on the measured intensity of the decoupled electromagnetic radiation is described by the following equation:
Hb=a·S ( Q bk ) −b

wherein a and b are constants and S(Q bk ) is a measurement signal correlating with the measured intensity of the decoupled electromagnetic radiation.

3. The method according to claim 1 , wherein, if the deviation between the current blood flow rate and the calibration blood flow rate is greater than the preset threshold value as determined by the computing and evaluation unit, in order to take account of the blood flow, the relationship describing the dependence of the concentration of the blood constituent on the measured intensity of the decoupled electromagnetic radiation is corrected as follows:
Hb=a· [ k·S ( Q b )] −b

wherein S(Q b ) is the measurement signal correlating with the measured intensity of the decoupled electromagnetic radiation and k is the correction factor.

4. The method according to claim 1 , further comprising, before the extracorporeal blood treatment is carried out:
ascertaining a relationship describing dependence of the correction factor on the blood flow rate; and
storing the relationship describing the dependence of the correction factor on the blood flow rate;
wherein ascertaining the correction factor for the blood flow rate during the extracorporeal blood treatment comprises calculating the correction factor from the relationship describing the dependence of the correction factor on the blood flow rate.

5. The method according to claim 4 , further comprising, at a start of the extracorporeal blood treatment:
determining that a deviation between the preset blood flow rate and the calibration blood flow rate is greater than the preset threshold value as determined by the computing and evaluation unit and calculating a first correction factor for a preset blood flow rate;
determining the concentration of the blood constituent taking account of the first correction factor;
calculating a second correction factor following a change in the blood flow rate during the extracorporeal blood treatment that is greater than the preset threshold value; and
determining the concentration of the blood constituent taking account of the second correction factor.

6. The method according to claim 4 , wherein the relationship describing the dependence of the correction factor on the blood flow rate is a polynomial of the first degree.

7. The method according to claim 1 , wherein ascertaining the correction factor comprises:
ascertaining a measured intensity of the decoupled electromagnetic radiation for the calibration blood flow rate;
adjusting the blood flow rate to the calibration blood flow rate for a preset time interval; and
measuring the electromagnetic radiation decoupled through the one of the arterial hose line or the venous hose line from the blood for the current blood flow rate and for the calibration blood flow rate;
wherein the correction factor is calculated based on the electromagnetic radiation measured for the current blood flow rate and the calibration blood flow rate.

8. The method according to claim 7 , wherein a correction factor (k) is calculated according to the following equation:

k
=

S
⁡

(

Q
bk

)

S
⁡

(

Q

b
⁢

⁢
1

)

wherein S(Q b1 ) is a measurement signal correlating with the measured intensity of the decoupled electromagnetic radiation for current blood flow rate Q b1 and S(Q bk ) is a measurement signal correlating with the measured intensity of the decoupled electromagnetic radiation for calibration blood flow rate Q bk .

9. The method according to claim 7 , further comprising:
calculating a difference between the current blood flow rate and the calibration blood flow rate;
determining that the current blood flow rate is less than the calibration blood flow rate;
determining that the deviation between the current blood flow rate, and the calibration blood flow rate as determined by the computing and evaluation unit, is greater than the preset threshold value and less than a second preset threshold value; and
adjusting the blood flow rate to the calibration blood flow rate for a preset time interval.

10. The method according to claim 7 , further comprising:
setting an ultrafiltration rate at which fluid is withdrawn from the extracorporeal blood circuit during the pre

Assignees

• Fresenius Medical Care Deutschland Gmbh

Inventors

• Zhang Wei
• Bardorz Christoph
• Mueller Carsten
• Schulte Elke

Classifications

• A61M2205/3313

  used specific wavelengths · CPC title

• A61B5/14557 Primary

  specially adapted to extracorporeal circuits · CPC title

• A61B5/14525 Primary

  using microdialysis · CPC title

• G01N21/53

  within a flowing fluid, e.g. smoke · CPC title

• A61M1/3609

  Physical characteristics of the blood, e.g. haematocrit, urea · CPC title