Method for determining a patient's blood sodium level and artificial kidney for the application thereof

Claim 1

A method for determining the blood sodium level of a patient whose blood circulates through a first compartment of an exchanger of an artificial kidney, said first compartment being separated from a second compartment of the exchanger by a semipermeable membrane for permitting dialysis and ultrafiltration of the blood, said second compartment being disposed in a dialysis fluid circuit through which dialysis fluid passes, comprising the steps of: changing, in a selected manner, the conductivity of the dialysis fluid flowing into the second compartment of the exchanger; measuring, in response to the step of changing the conductivity of the dialysis fluid, the change in conductivity of the dialysis fluid flowing out of the second compartment of the exchanger; determining a lag time t L between the change in conductivity of the dialysis fluid flowing into the second compartment of the exchanger and the corrresponding measured change in conductivity of dialysis fluid flowing out of the second compartment of the exchanger; determining an equilibrium conductivity value of the dialysis fluid in the second compartment of the exchanger for which the conductivity of the dialysis fluid at outflow from the second compartment at a time t is substantially equal to the conductivity of the dialysis fluid at inflow into the second compartment at a time t'=t-t L ; and determining the sodium concentration in the patient's blood in accordance with the determined equilibrium conductivity value.

Claim 2

A method for determining the blood sodium level of a patient whose blood circulates through a first compartment of an exchanger of an artificial kidney, said first compartment being separated from a second compartment of the exchanger by a semipermeable membrane for permitting dialysis and ultrafiltration of the blood, said second compartment being disposed in a dialysis fluid circuit through which dialysis fluid passes, comprising the steps of: changing, in a selected manner, the conductivity of the dialysis fluid flowing into the second compartment of the exchanger; measuring, in response to the step of changing the conductivity of the dialysis fluid, the change in conductivity of the dialysis fluid flowing out of the second compartment of the exchanger; determining a lag time t L between the change in conductivity of the dialysis fluid flowing into the second compartment of the exchanger and the corrresponding measured change in conductivity of dialysis fluid flowing out of the second compartment of the exchanger; determining an equilibrium conductivity value of the dialysis fluid in the second compartment of the exchanger for which the conductivity of the dialysis fluid at outflow from the second compartment at a time t is substantially equal to the conductivity of the dialysis fluid at inflow into the second compartment at a time t'=t-t L ; and determining the sodium concentration in the patient's blood in accordance with the determined equilibrium conductivity value.

Claim 5

The method of claims 2 or 3 wherein the conductivity of the dialysis fluid flowing into the second compartment of the exchanger is changed in a substantially continuous manner.

Claim 7

The method of claims 1, 2, or 3, wherein the step of determining the lag time t L includes the substeps of: determining a time to corresponding to the initialization of the change in conductivity of the dialysis fluid flowing into the second compartment of the exchanger; monitoring, as a function of time, changes in the conductivity of the dialysis fluid flowing out of the second compartment to determine a time t 1 corresponding to the initialization of the change in conductivity of dialysis fluid flowing out of the second compartment; determining the lag time t L in accordance with the interval between times t l and t o .

Claim 8

The method of claims 1, 2, 3, or 5, wherein the artificial kidney includes a conductimeter positioned in the dialysis fluid circuit upstream of the second compartment of the exchanger relative to the flow of dialysis fluid in the dialysis fluid circuit, and wherein the method includes the further step of measuring, with the conductimeter, the conductivity of the dialysis fluid flowing into the second compartment.

Claim 9

The method of claims 1, 2, 3, or 5, wherein the artificial kidney includes a monitoring device including means for changing the conductivity of the dialysis fluid flowing into the second compartment in accordance with a predetermined pattern, and wherein the step of changing the conductivity of the dialysis fluid flowing into the second compartment includes the substep of monitoring, with the monitoring means, the predetermined pattern of the changing means to determine the conductivity of the dialysis fluid flowing into the second comparment of the exchanger.

Claim 10

A method for determining the blood sodium level of a patient's blood circulating through a first compartment of an exchanger of an artificial kidney, said exchanger including a semipermeable membrane separating the first compartment from a second compartment of the exchanger through which dialysis fluid in a dialysis fluid circuit passes, said membrane being adapted to permit the dialysis and ultrafiltration of the blood from between the first and second compartments, comprising the steps of: selectively changing the conductivity of dialysis fluid flowing into the second compartment of the exchanger; monitoring the conductivity of the dialysis fluid flowing into the second compartment to determine a time t o at which the conductivity of the dialysis fluid flowing into the second compartment changes in response to the step of selectively changing the conductivity; monitoring the conductivity of the dialysis fluid flowing out of the second compartment to determine a time t l at which the conductivity of the dialysis fluid flowing out of the second compartment changes in response to the step of selectively changing the conductivity; determining a lag time t L between initialization of the change in conductivity of the dialysis fluid flowing into and out of the second compartment in accordance with the difference between the times t 0 and t 1 ; determining an equilibrium value between the conductivity of the dialysis fluid in the second compartment and the conductivity of the blood in the first compartment in accordance with the monitored values of conductivity of the dialysis fluid and the lag time t L ; and determining the patient's blood sodium level in accordance with the determined equilibrium conductivity value.

Claim 11

A method for determining the blood sodium level of a patient's blood circulating through a first compartment of an exchanger of an artificial kidney, said exchanger including a semipermeable membrane separating the first compartment from a second compartment of the exchanger through which dialysis fluid in a dialysis fluid circuit passes, said membrane being adapted to permit the dialysis and ultrafiltration of the blood from between the first and second compartments, comprising the steps of: selectively changing the conductivity of dialysis fluid flowing into the second compartment of the exchanger; monitoring the conductivity of the dialysis fluid flowing into the second compartment to determine a time t o at which the conductivity of the dialysis fluid flowing into the second compartment changes in response to the step of selectively changing the conductivity; monitoring the conductivity of the dialysis fluid flowing out of the second compartment to determine a time t l at which the conductivity of the dialysis fluid flowing out of the second compartment changes in response to the step of selectively changing the conductivity; determining a lag time t L between initialization of the change in conductivity of the dialysis fluid flowing into and out of the second compartment in accordance with the difference between the times t 0 and t 1 ; determining an equilibrium value between the conductivity of the dialysis fluid in the second compartment and the conductivity of the blood in the first compartment in accordance with the monitored values of conductivity of the dialysis fluid and the lag time t L ; and determining the patient's blood sodium level in accordance with the determined equilibrium conductivity value.