Method of measuring transcutaneous access blood flow

• US 20020128545A1
• Filed: 12/29/2000
• Published: 09/12/2002
• Est. Priority Date: 12/29/2000
• Status: Active Grant

• Current Assignee: Fresenius Medical Care Holdings Incorporated (Fresenius Medical Care AG)
• Original Assignee: HEMA Metrics Incorporated
• Inventors: Miller, David R., Bell, David A., Steuer, Robert R.
• Granted Patent: US 6,746,407 B2
• Time in Patent Office: Days
• US Class Current: 600/345
• CPC Class Codes: A61B 5/0275 using tracers, e.g. dye dilution
• CPC Class Codes: A61M 1/3609 Physical characteristics of the blood, e.g. haematocrit, urea
• CPC Class Codes: A61M 1/3653 Interfaces between patient blood circulation and extra-corporal blood circuit
• CPC Class Codes: A61M 1/3655 Arterio-venous shunts or fistulae
• CPC Class Codes: A61M 1/3656 Monitoring patency or flow at connection sites; Detecting disconnections

Abstract

Indicator dilution techniques are used to measure vascular access flow rates during routine hemodialysis. A bolus injection port is used to infuse a specific volume (V_i) of an indicator diluent, such as saline or dye, into the patient cardiovascular circuit by one of the following:

1. Needle injection of a known volume (bolus) of indicator diluent directly into the access site in the presence or absence of the hemodialysis circuit.

2. Infusion of an indicator diluent into the arterial, venous line upstream of the venous needle.

3. Turning the ultrafiltration of the dialysis delivery system from OFF to ON and OFF again over a predetermined time period.

4. In a hemodialysis circuit, turning on the hemodialysis pump and using the priming saline volume as a single saline bolus.

A transdermal sensor is used to measure the percent change in a blood parameter. The sensor is positioned directly over the vascular access site a prescribed distance downstream of the injection site and upstream of the access-vein connection. The sensor employs emitter and detector elements at multiple spacings (d₁, d₂) for the purpose of measuring the bulk absorptivity (α) of the area immediately surrounding and including the access site, and the absorptivity (α₀) of the tissue itself.

Claims

1. A method of measuring a blood parameter transcutaneously in the vascular system of a patient comprising the steps of:

perturbing a region of the vascular system;

using a sensor placed on the skin of a patient to transcutaneously measure the perturbation over a predetermined period of time at a measurement site downstream of the perturbation region in the vascular system; and

calculating the blood parameter based on the measured perturbation.

2. The method of claim 1, wherein the region that is perturbed is a vascular access site, and the perturbation is accomplished by injecting a marker into an upstream end of the vascular access site.

3. The method of claim 2, wherein the marker is a saline solution.

4. The method of claim 2, wherein the marker is tagged red blood cells.

5. The method of claim 1, wherein the region that is perturbed is a vascular access site, and the perturbation is accomplished by changing a parameter of the blood.

6. A method of transcutaneously measuring access blood flow in a hemodialysis circuit including a vascular access site having a needle site, a dialyzer, and a dialyzer line connecting the dialyzer to the vascular access site at the needle site, the method comprising the steps of:

placing a sensor capable of determining the relative changes in a blood parameter in the access blood flowing under the skin, on the skin over the vascular access site downstream of the needle site;

using the sensor to output a signal proportional to the blood parameter in the vascular access site;

recording the signal with a monitoring system associated with the sensor;

obtaining a stable baseline value of the blood parameter in the vascular access site;

after a baseline value of the blood parameter in the vascular access site is obtained, perturbing the vascular access site; and

using the signals produced from the time the vascular access site is perturbed to the time the signal returns to the baseline value to calculate access blood flow based on the ratio of percent change in the blood parameter to a time-dependent blood parameter using the monitoring system.

7. The method of claim 6, wherein access blood flow is calculated using a transient formulation.

8. The method of claim 6, wherein access blood flow is calculated using a steady state formulation.

9. The method of claim 6, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

10. A method of transcutaneously measuring access blood flow in a hemodialysis circuit including a vascular access site having an arterial needle site and a venous needle site downstream of the arterial needle site, a dialyzer having an inlet and an outlet, a dialysis arterial line connecting the dialyzer inlet to the arterial needle site, and a dialysis venous line connecting the dialyzer outlet to the venous needle site, the method comprising the steps of:

placing a sensor capable of determining the relative changes in hematocrit in the access blood flowing under the skin, on the skin over the vascular access site downstream of the venous needle site;

using the sensor to output a signal proportional to the hematocrit in the vascular access site (H_a);

recording the signal with a monitoring system associated with the sensor;

obtaining a stable baseline H_a value;

after a stable is H_a obtained, injecting a known volume (V) of a reference diluent into the dialysis venous line upstream of the sensor; and

using the signals produced from the time the diluent is injected to the time the signal returns to the baseline value to calculate access blood flow based on the ratio of percent change in hematocrit Δ

H to a time-dependent hematocrit H using the monitoring system.

11. The method of claim 10, wherein access blood flow is calculated using a transient formulation.

12. The method of claim 10, wherein access blood flow is calculated using a steady state formulation.

14. The method of claim 13, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

15. The method of claim 13, wherein the transdermal sensor is placed over the access site.

17. The method of claim 16, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

18. The method of claim 16, wherein the transdermal sensor is placed over the access site.

20. The method of claim 19, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

21. The method of claim 19, wherein the transdermal sensor is placed directly on the skin over the access site.

13. A method of transcutaneously measuring access blood flow comprising the steps of:

infusing a specific volume (V_i) of an indicator diluent into a patient cardiovascular circuit at an access site in the presence of a hemodialysis circuit to effect a change in a blood parameter; and

using a transdermal sensor to measure the percent change in the parameter.

16. A method of transcutaneously measuring access blood flow comprising the steps of:

infusing a specific volume (V_i) of an indicator diluent into a patient cardiovascular circuit at an access site in the absence of a hemodialysis circuit to effect a change in a blood parameter; and

using a transdermal sensor to measure the percent change in the parameter.

19. A method of transcutaneously measuring access blood flow in a hemodialysis circuit including a vascular access site having an arterial needle site and a venous needle site downstream of the arterial needle site, and a dialyzer having an inlet and an outlet, a dialysis arterial line connecting the dialyzer inlet to the arterial needle site, and a dialysis venous line connecting the dialyzer outlet to the venous needle site, the method comprising the steps of:

placing over the vascular access site downstream of the venous needle site a transdermal sensor capable of accurately determining the relative changes in a blood parameter in the access blood flowing directly under the skin;

infusing a specific volume (V_i) of an indicator diluent into the patient cardiovascular circuit at one of the arterial line and the venous line upstream of the sensor to effect a change in the blood parameter; and

using the transdermal sensor to measure the percent change in the parameter.

22. A method of transcutaneously measuring access blood flow in a hemodialysis circuit, the method comprising the steps of:

infusing a specific volume (V_i) of an indicator diluent into the patient cardiovascular circuit by turning the ultrafiltration of the dialysis delivery system from OFF to ON and OFF again over a predetermined time period to effect a change in a blood parameter; and

using a transdermal sensor to measure the percent change in the parameter.

23. The method of claim 22, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

24. The method of claim 22, wherein the transdermal sensor is placed over a vascular access site of the hemodialysis circuit.

26. The method of claim 25, wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.

27. The method of claim 25, wherein the transdermal sensor is placed over a vascular access site of the hemodialysis circuit.

25. A method of transcutaneously measuring access blood flow in a hemodialysis circuit, the hemodialysis circuit including a hemodialysis pump and employing a priming saline volume, the method comprising the steps of:

infusing the priming saline volume into the hemodialysis circuit by turning on the hemodialysis pump; and

using a transdermal sensor to measure the percent change in the parameter.