Method of measuring transcutaneous access blood flow

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 into the patient cardiovascular circuit by one of the following: 1. Needle injection of a known volume 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 (d 1 , d 2 ) for the purpose of measuring the bulk absorptivity (α) of the area immediately surrounding and including the access site, and the absorptivity (α o ) of the tissue itself.

What is claimed is:  
     
         1 . A method of measuring a blood parameter transcutaneously in the vascular system of a patient, the vascular system having a vascular access site and a needle site in the vascular access site, comprising the steps of: 
 perturbing a region of the vascular system;    using a sensor placed on the skin of a patient over the access site downstream of the needle site 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 . The method of  claim 1 , wherein the blood parameter is macroscopic.  
     
     
         7 . The method of  claim 1 , wherein the blood parameter is microscopic.  
     
     
         8 . A method of transcutaneously measuring access blood flow comprising the steps of: 
 infusing a specific volume (Vi) 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 at a measurement site downstream of where the indicator is infused.    
     
     
         9 . The method of  claim 8 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         10 . The method of  claim 8 , wherein the needle site comprises an arterial needle site and a venous needle site downstream of the arterial needle site, and wherein the transdermal sensor is placed between the venous needle site and the access site/vein connection.  
     
     
         11 . The method of  claim 8 , wherein the blood parameter is macroscopic.  
     
     
         12 . The method of  claim 8 , wherein the blood parameter is microscopic.  
     
     
         13 . The method of  claim 8 , wherein the blood parameter is macroscopic.  
     
     
         14 . The method of  claim 8 , wherein the blood parameter is microscopic.  
     
     
         15 . A method of transcutaneously measuring access blood flow in a patient cardiovascular circuit having a vascular access site and a needle site in the vascular access site, 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 placed on the skin of the patient over the access site downstream of the needle site to measure the percent change in the parameter.    
     
     
         16 . The method of  claim 15 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         17 . The method of  claim 15 , wherein the transdermal sensor is placed over the access site.  
     
     
         18 . A method of transcutaneously measuring access blood flow through the measurement of percentage change in a blood parameter, 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.    
     
     
         19 . The method of  claim 18 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         20 . The method of  claim 18 , wherein the transdermal sensor is placed directly on the skin between the venous line and the access site/vein connection.  
     
     
         21 . The method of  claim 18 , wherein the blood parameter is macroscopic.  
     
     
         22 . The method of  claim 18 , wherein the blood parameter is microscopic.  
     
     
         23 . A method of transcutaneously measuring access blood flow in a hemodialysis circuit through the measurement of percentage change in a blood parameter, the method comprising the steps of: 
 infusing a specific volume (V i ) of an indicator diluent into the patient cardiovascular circuit through an arterial or venous line 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 placed on the skin of the patient over the vascular access downstream of the arterial and venous lines to measure the percent change in the parameter.    
     
     
         24 . The method of  claim 23 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         25 . The method of  claim 23 , wherein the transdermal sensor is placed over a vascular access site of the hemodialysis circuit.  
     
     
         26 . The method of  claim 23 , wherein the blood parameter is macroscopic.  
     
     
         27 . The method of  claim 23 , wherein the blood parameter is microscopic.  
     
     
         28 . A method of transcutaneously measuring access blood flow in a hemodialysis circuit including a vascular access site having a needle site, 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 placed on the skin of the patient over the access site downstream of the needle site to measure the percent change in the parameter.    
     
     
         29 . The method of  claim 28 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         30 . The method of  claim 28 , wherein the vascular access site comprises an arterial needle site and a venous needle site downstream of the arterial needle site and wherein the transdermal sensor is placed between the venous needle site and the access site/vein connection.  
     
     
         31 . The method of  claim 28 , wherein the blood parameter is macroscopic.  
     
     
         32 . The method of  claim 28 , wherein the blood parameter is microscopic.  
     
     
         33 . A method of transcutaneously measuring access blood flow through the measurement of percentage change in a blood parameter, in a hemodialysis circuit having a vascular access site that includes 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 dialyzer venous line connecting the dialyzer outlet to the venous needle site, the method comprising the steps of: 
 placing on the skin of the patient downstream of the venous needle site a sensor having a field of view so that at least a portion of the access site is within the field of view of the sensor and that a portion of the tissue surrounding the access site occupies the remainder of the field of view;    using the sensor to output a first signal containing information about both the surrounding tissue and the portion of the access site;    using the sensor to output a second signal containing information about the surrounding tissue;    mathematically manipulating the first and second signals to provide a stable baseline value of the blood parameter in the vascular access site;    after obtaining the baseline value of the blood parameter in the vascular access site, injecting a diluent into the access site upstream of the sensor at an average flow rate;    monitoring the first and second signals from the time the diluent is injected until the time the signal returns to the baseline value; and    calculating access blood flow based on the monitored first and second signals.    
     
     
         34 . The method of  claim 33 , wherein the blood parameter chosen to calculate access blood flow is Hematocrit.  
     
     
         35 . The method of  claim 33 , wherein the reference diluent is injected at a predetermined average flow rate.  
     
     
         36 . The method of  claim 33 , wherein the reference diluent is injected at a uniform and constant flow rate.  
     
     
         37 . The method of  claim 33 , wherein the reference diluent is introduced into dialysis venous line.  
     
     
         38 . The method of  claim 33 , wherein the reference diluent is introduced through the dialysis arterial line.  
     
     
         39 . A method of transcutaneously measuring access blood flow in a hemodialysis circuit, the hemodialysis circuit including a dialyzer, a dialyzer pump upstream of the dialyzer, a hemodialysis access site previously established in a patient for the purpose of carrying out dialysis and having a vein connection and an artery connection, an arterial needle inserted into the hemodialysis access site at an arterial needle site on the arterial, upstream side of the hemodialysis circuit, an intake catheter connecting the arterial needle to the dialyzer pump, a venous needle inserted into the hemodialysis access site at a venous needle site on the venous, downstream side of the dialyzer, the hemodialysis circuit 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 placed over the access site between the venous needle site and the access/vein connection to measure the percent change in the parameter.    
     
     
         40 . The method of  claim 39 , wherein the blood parameter is selected from the group consisting of bulk density, flow energy, hematocrit, and red cell oxygen content.  
     
     
         41 . The method of  claim 39 , wherein the priming saline volume is used as a single 10 second saline bolus when the dialyzer pump flow rate Qb=300 ml/min.