Method of monitoring the bicarbonate content and the sodium content of a dialysis solution

Abstract

The present invention relates to a method of monitoring the bicarbonate content and the sodium content of a dialysis solution, wherein the dialysis solution is prepared while adding a bicarbonate component and an acidic sodium component, and wherein the method comprises the following steps: a. adding the acidic sodium component and measuring the conductivity (LF.sub.ist,Na); b. adding the bicarbonate component and measuring the increase in conductivity (ΔLF.sub.ist,BiC) caused by adding the bicarbonate component; c. determining the increase in conductivity (ΔLF.sub.exp,Bic) expected due to the addition of the bicarbonate component; d. checking whether the measured increase in conductivity (ΔLF.sub.ist,Bic) lies in an expected range of the increase in conductivity (ΔLF.sub.exp,Bic); e. determining the total conductivity (LF.sub.exp,D) expected after the addition of the bicarbonate component and of the acidic sodium component; f. measuring the total conductivity (LF.sub.ist,D) after the addition of the bicarbonate component and of the acidic sodium component; and g. checking whether the measured total conductivity (LF.sub.ist,D) lies in an expected range of the total conductivity (LF.sub.exp,D),
wherein the measurement of the conductivity in accordance with step a.; the measurement of the increase in conductivity in accordance with step b.; and the measurement of the total conductivity in accordance with step f. are carried out by one and the same conductivity measurement cell.

Claims

1. A method of monitoring the bicarbonate content and the sodium content of a dialysis solution, wherein the dialysis solution is prepared while adding a bicarbonate component and an acidic sodium component, and wherein the method comprises the following steps: a. adding the acidic sodium component and measuring the conductivity (LF.sub.ist,Na); b. adding the bicarbonate component and measuring the increase in conductivity (ΔLF.sub.ist,Bic) caused by adding the bicarbonate component; c. determining the increase in conductivity (ΔLF.sub.exp,Bic) expected due to the addition of the bicarbonate component; d. checking whether the measured increase in conductivity (ΔLF.sub.ist,Bic) lies in an expected range of the increase in conductivity (ΔLF.sub.exp,Bic); e. determining the total conductivity (LF.sub.exp,D) expected after the addition of the bicarbonate component and of the acidic sodium component; f. measuring the total conductivity (LF.sub.ist,D) after the addition of the bicarbonate component and of the acidic sodium component; and g. checking whether the measured total conductivity (LF.sub.ist,D) lies in an expected range of the total conductivity (LF.sub.exp,D), wherein the measurement of the conductivity in accordance with step a.; the measurement of the increase in conductivity in accordance with step b.; and the measurement of the total conductivity in accordance with step f. are carried out by one and the same conductivity measurement cell.

2. The method in accordance with claim 1, characterized in that the acidic sodium component is added first; and in that the measurement of the increase in conductivity (ΔLF.sub.ist,Bic) in accordance with step b. is obtained in that the measured conductivity (LF.sub.ist,Na) after the addition of the acidic sodium component is deducted from the measured total conductivity (LF.sub.ist,D) in accordance with step f.

3. The method in accordance with claim 1, characterized in that the expected increase in conductivity (ΔLF.sub.exp,Bic) in accordance with step c. is calculated from the substances of the bicarbonate component.

4. The method in accordance with claim 1, characterized in that the expected range in accordance with step d. extends from a value 25% below the expected increase in conductivity (ΔLF.sub.exp,Bic) up to a value 25% above the expected increase in conductivity (ΔLF.sub.exp,Bic).

5. The method in accordance with claim 1, characterized in that the expected total conductivity (ΔLF.sub.exp,D) in accordance with step e. is calculated from the substances of the acidic sodium component and of the bicarbonate component.

6. The method in accordance with claim 1, characterized in that the expected range for the total conductivity extends from a value 5% below the expected total conductivity (ΔLF.sub.exp,D) up to a value 5% above the expected total conductivity (ΔLF.sub.exp,D).

7. The method in accordance with claim 1, characterized in that the prepared dialysis solution is decoupled from the dialyzer of a dialysis machine from time to time for monitoring the bicarbonate content and the sodium content of a dialysis solution on a change in concentration.

8. The method in accordance with one claim 1, characterized in that an alarm and/or an output of corresponding information to a user is/are generated on an exceeding or a falling below of the range.

9. The method in accordance with claim 8, characterized in that an alarm is triggered and/or the output of corresponding information takes place as soon as the range for the sodium content or the range for the bicarbonate content is exceeded or fallen below depending on which exceeding or falling below takes place the sooner.

10. A preparation device for preparing a dialysis solution from at least two components, wherein the preparation device has a container having a bicarbonate component (“bicarbonate container”) and a container having an acidic sodium component (“sodium container”); wherein the preparation device has a conductivity measurement cell for measuring the conductivity (LF.sub.ist,Na) of a fluid after addition of the acidic sodium component to the fluid; a conductivity measurement cell for the measurement of the increase in conductivity (ΔLF.sub.ist,Bic) caused by addition of the bicarbonate component to the fluid; and a conductivity measurement cell for the measurement of the total conductivity (LF.sub.ist,D) of the fluid containing the acidic sodium component and the bicarbonate component such that a dialysis solution is prepared; and wherein the preparation device is configured such that it checks whether the increase in conductivity (ΔLF.sub.ist,Bic) caused by the addition of the bicarbonate component is in an expected range of the increase in conductivity (ΔLF.sub.exp,Bic) and whether the measured total conductivity (LF.sub.ist,D) is in an expected range of the total conductivity (LF.sub.exp,D), with the named conductivity measurement cells being one and the same conductivity measurement cell, and the one and the same conductivity measurement cell being arranged downstream of the sodium container and downstream of the bicarbonate container.

11. The preparation device in accordance with claim 10, characterized in that the preparation device has an alarm unit and/or an output unit for outputting information to a user which is/are configured such that an alarm is triggered and/or information is output when the exceeding or falling below of the range is detected.

12. The preparation device in accordance with claim 10, characterized in that the preparation device has a main line into which a feed line in communication with the bicarbonate container opens and into which a further feed line in communication with the sodium container opens; and/or in that the main line is in communication with a container or with a source for water; and/or in that the conductivity measurement cell is arranged downstream of both openings of the feed lines.

13. The preparation device in accordance with claim 10, characterized in that the preparation device can be brought into fluid communication with a dialyzer of a dialysis machine so that the prepared dialysis solution flows through the dialysis side of the dialyzer; and in that the preparation device has a bypass line which leads around the dialyzer so that the prepared dialysis solution can be led around the dialyzer at times.

14. A dialysis machine having the preparation device in accordance with claim 10.

15. The preparation device of claim 12, wherein the source for water is RO water.

Description

(1) Further details and advantages of the invention will be explained in more detail with reference to an embodiment shown in the drawing.

(2) FIG. 1 shows a schematic representation of the sodium and bicarbonate monitoring by means of two independent limit value windows (ranges) using a single conductivity measurement cell.

(3) FIG.2 shows a preparation device for preparing a dialysis solution from at least two components.

(4) The embodiment described in the following represents a possibility of additionally monitoring with respect to the required limits by a conductivity measurement of the dialysis solution in a two-component system without more than one conductivity measurement cell having to be used for this purpose. It must be pointed out at this point that the invention is not restricted to adding exactly two components; more than two components can also be added.

(5) In accordance with the invention, a bicarbonate component and an acidic sodium component can be metered in separately. The metering can take place, for example, into a line in which water, preferably RO water or a solution, flows which was obtained from a mixture of one of the components with water or RO water.

(6) The expected total conductivity and the expected increase in conductivity after adding the bicarbonate component are to be calculated on the basis of the respective substances or on the basis of the conductivity of the dialysis solution to be theoretically expected.

(7) In accordance with FIG. 1, the conductivity to be expected, i.e. the total conductivity LF.sub.exp,D of the completed dialysis solution to be expected is calculated from the latter's substances with the aid of a mathematical formula.

(8) The operating system, i.e. the preparation device, in which the dialysis solution is mixed suffers from different tolerances. This tolerance chain can have the result that the actually measured total conductivity LF.sub.ist,D of the completed dialysis solution, i.e. the dialysis solution containing the acidic sodium component and the bicarbonate component, deviates from the theoretically calculated expected value LF.sub.exp,D.

(9) As can be seen from the left hand side of FIG. 1 (“Na monitoring”), the total conductivity LF.sub.exp,D to be expected is composed of the expected (nominal) conductivity of the acidic sodium component LF.sub.exp,Na and of the expected (nominal) conductivity of the bicarbonate component LF.sub.exp,Bic.

(10) A 5% deviation of the sodium concentration with respect to the calculated expected value LF.sub.exp,D, i.e. from the desired value, can be determined by monitoring the total conductivity LF.sub.exp,D for a deviation of 5% shown at the left hand side of FIG. 1. The range in which the total conductivity may be thus amounts to 10% and extends in each case by 5% upward and downward from the expected value.

(11) The right hand side of FIG. 1 (“Bic monitoring”) has the following structure:

(12) The conductivity LF.sub.ist,Na is the measured conductivity of the solution after the addition of the acidic sodium component.

(13) The expected increase in conductivity by adding the bicarbonate component to this solution is marked by ΔLF.sub.exp,Bic at the right hand side of FIG. 1. It is calculated from the difference between the expected total conductivity LF.sub.exp,D and the expected conductivity of the acidic sodium component LF.sub.exp,Na.

(14) The bicarbonate component typically contains sodium in addition to bicarbonate. The procedure is as follows in order not to have to take account of the influence of the acidic component containing sodium itself, of the metering of the acidic sodium component suffering from tolerances, and of additional interference parameters such as the basic conductivity of the water used in the calculation of the desired value of the conductivity of the bicarbonate component:

(15) In a first step, only the acidic sodium component and the required water is metered in (Metering 1) and is led past the conductivity measurement cell. The conductivity LF.sub.ist,Na obtained in this respect contains all the tolerances of the operating system and serves as an offset for the monitoring limits of the bicarbonate which still have to be determined.

(16) In the second step, the bicarbonate component is added (Metering 2) so that all the components are present and the dialysis solution is completely initially mixed. A measured total conductivity LF.sub.ist,D of the dialysis solution is adopted. The already determined conductivity of the dialysis solution containing sodium (without bicarbonate) LF.sub.ist,Na is deducted from the measured total conductivity LF.sub.ist,D and the actual contribution of the bicarbonate component ΔLF.sub.ist,Bic to the total conductivity is thus measured.
ΔLF.sub.ist,Bic=LF.sub.ist,D−LF.sub.ist,Na

(17) The offset of the acidic sodium component (including water and tolerances) determined in step 1 is thus eliminated from the measured total conductivity LF.sub.ist,D by calculation and the contribution of the bicarbonate component to the conductivity is determined in this manner.

(18) The monitoring limits can be calculated from the increase in conductivity to be theoretically expected due to the addition of the bicarbonate component ΔLF.sub.exp,Bic (desired value) and thus relate to the required desired value. In the embodiment in accordance with the right hand side of FIG. 1, the monitoring limits extend from a value 25% below ΔLF.sub.exp,Bic to 25% above ΔLF.sub.exp,Bic, i.e. the permitted increase in conductivity caused by the addition of the bicarbonate solution lies in the interval ΔLF.sub.exp,Bic*0.75 to ΔLF.sub.exp,Bic*1.25.

(19) When taking account of the limit values for the total conductivity, two independent monitoring windows thus result for sodium and bicarbonate which can detect the respective concentration deviations from the desired value in accordance with the demands of the standard.

(20) To ensure a two-channel design, provision is preferably made that all the theoretical calculations of expected values are carried out by a protection system which is independent of the operating system of the dialysis machine.

(21) Changes in the concentrations during the treatment such as the shift in the sodium concentration and/or bicarbonate concentration can be taken into account using the procedure in accordance with the invention. A repeat calibration of the system, i.e. the repeat preparation of a dialysis solution having correspondingly changed concentration values could take place, for example, during a bypass, i.e. during a hydraulic decoupling of the preparation device from the water part of the dialysis machine. A theoretical new calculation of the monitoring windows would also be conceivable without a repeat calibration on a change of the concentration under certain circumstances.

(22) On a change of concentrate or on a canister change, the method in accordance with a first variant has to be carried out again. In the event that a somewhat larger uncertainty can be accepted, a theoretical new calculation of the bicarbonate limit window is possible on a change of the concentrate or on a canister change in accordance with a second variant. The sodium limit window can be calculated again at any time. The sodium concentration can furthermore always be measured again.

(23) An abruptly occurring error in the metering in of the acidic sodium component can have the result due to the simultaneous monitoring of the sodium concentration and of the bicarbonate concentration by means of a single conductivity measurement cell that an alarm is triggered because the bicarbonate monitoring window has been left. Due to the fact that a single conductivity measurement cell, which measures the total conductivity of the dialysis solution in normal operation, cannot make any distinction as to the component from which the error emanates, the monitoring window which is left first will trigger an alarm. It can be precluded with the help of risk management that, for example, metering errors of the pumps conveying the components can occur in the opposite direction. This could result in a mutual cancellation of the errors in the conductivity under certain circumstances. Multiple errors are precluded from the viewpoint or risk management.

(24) Referring to FIG. 2, a preparation device 100 prepares a dialysis solution 134 from at least two components. Preparation device 100 includes a container 108 having a bicarbonate component therein (“bicarbonate container,”) and a container 110 having an acidic sodium component therein (“sodium container”). Preparation device 100 includes a conductivity measurement cell 111 having sensors 112 for measuring the increase in conductivity (LF.sub.ist,Na) of dialysis solution 134 after the addition of the acidic sodium component, for measuring the increase in conductivity (ΔLF.sub.ist,Bic) of dialysis solution 134 after the addition of the component containing bicarbonate, and for the measuring the total conductivity (LF.sub.ist,D) of dialysis solution 134 after the addition of both the acidic sodium component and the bicarbonate component. Conductivity measurement cell 111 is arranged downstream of sodium container 110 and downstream of bicarbonate container 108. Preparation device 100 is configured such that it checks whether the increase in conductivity (ΔLF.sub.ist,Bic) caused by the addition of the bicarbonate component is within an expected range of increase in conductivity (ΔLF.sub.exp,Bic) and whether the measured total conductivity (LF.sub.ist,D) is within an expected range of total conductivity (LF.sub.exp,D).

(25) Preparation device 100 includes an alarm unit 114 and an output unit 116 for outputting information to a user and that are configured such that an alarm is triggered and information is output when conductivity exceeding or falling below a range is detected.

(26) Preparation device 100 includes a main line 118 into which a feed line 120, that is in communication with bicarbonate container 108, opens at an opening 126. A feed line 122 in communication with sodium container 110 opens at an opening 128 into main line 118. Main line 118 is also in communication with a container 124 containing a source of water. Conductivity measurement cell 111 is arranged downstream of both openings 126 and 128 and feed lines 120 and 122.

(27) A dialysis machine 132 is provided that comprises a dialyzer 130 having a dialysate side 136 separated from a blood side by a semi-permeable membrane 140. Preparation device 100 can be brought into fluid communication with dialyzer 130 of dialysis machine 132 so that prepared dialysis solution 134 flows through dialysate side 136 of dialyzer 130. Preparation device 100 also includes a bypass line 138 that leads around dialyzer 130 so that the prepared dialysis solution 134 can be led around dialyzer 136, at times.

(28) It must be pointed out that the term “conductivity” includes every parameter which correlates with the conductivity or with the content of sodium and bicarbonate. The term “conductivity measurement cell” accordingly includes every sensor by means of which the conductivity or a parameter correlating therewith or with the content of sodium and bicarbonate can be measured.

(29) The local order in which the acidic sodium component and the bicarbonate component are added in the hydraulic system of the dialysis machine during normal operation does not play any role for the method.

(30) It is generally pointed out that all or some of the steps of the method in accordance with the invention can be carried out continuously and/or a multiple of times and/or cyclically and/or periodically.