MEASURING HEMATOCRIT AND ESTIMATING HEMOGLOBIN VALUES WITH A NON-INVASIVE, OPTICAL BLOOD MONITORING SYSTEM
First Claim
1. In a hemodialysis system, a method for monitoring at least one blood constituent, the method comprising the steps of:
- providing a blood chamber in extracorporeal tubing through which a patient'"'"'s blood flows for hemodialysis;
providing a ratiometric model within a controller for an optical monitoring device that determines a hematocrit value as a function of at least a detected value of light intensity having a first wavelength and a detected value of light intensity having a second wavelength, wherein the ratiometric model is calibrated at least in part by testing the ratiometric model by using the optical monitoring device with whole blood from a supply of blood preserved in a first anticoagulant, measuring the hematocrit value of whole blood from the same supply of blood preserved in the first anticoagulant using an in vitro method, and calibrating the ratiometric model to the measured hematocrit value taken using the in vitro method;
emitting light at a first wavelength through the extracorporeal blood chamber and the patient'"'"'s blood flowing through the blood chamber;
emitting light at the second wavelength through the extracorporeal blood chamber and the patient'"'"'s blood flowing through the blood chamber;
detecting the intensity of the light at the first wavelength after it has passed through the extracorporeal blood chamber and the patient'"'"'s blood flowing therethrough;
detecting the intensity of the light at the second wavelength after it passes through the extracorporeal blood chamber and the blood flowing therethrough;
calculating a hematocrit value using the ratiometric model from at least the detected light intensity at the first wavelength and the detected light intensity at the second wavelength; and
scaling the hematocrit value calculated by the ratiometric model by a scaling factor to result in a scaled hematocrit value.
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Abstract
An optical blood monitoring system with a ratiometric model determines hematocrit values for a hemodialysis patient, from which hemoglobin values for the patient are estimated. The ratiometric model is calibrated, normally against a cell counter, using blood from a blood bank. The blood from a blood bank is preserved in a long term preservative which is typically different than that found in clinical settings. The hematocrit value determined by the ratiometric model is scaled by scaling factor so that the estimated hemoglobin level output from the monitor consistently matches that measured in a clinical setting. The hematocrit scaling factor is substantially about 1.033 when the patient'"'"'s blood sample is stored in a short term preservative ethylene diamine tetra acetic, and is substantially about 1.06 when the hematocrit is measured in the blood sample without preservative being added to the blood sample. The hemoglobin value can also be adjusted for altitude.
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Citations
20 Claims
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1. In a hemodialysis system, a method for monitoring at least one blood constituent, the method comprising the steps of:
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providing a blood chamber in extracorporeal tubing through which a patient'"'"'s blood flows for hemodialysis; providing a ratiometric model within a controller for an optical monitoring device that determines a hematocrit value as a function of at least a detected value of light intensity having a first wavelength and a detected value of light intensity having a second wavelength, wherein the ratiometric model is calibrated at least in part by testing the ratiometric model by using the optical monitoring device with whole blood from a supply of blood preserved in a first anticoagulant, measuring the hematocrit value of whole blood from the same supply of blood preserved in the first anticoagulant using an in vitro method, and calibrating the ratiometric model to the measured hematocrit value taken using the in vitro method; emitting light at a first wavelength through the extracorporeal blood chamber and the patient'"'"'s blood flowing through the blood chamber; emitting light at the second wavelength through the extracorporeal blood chamber and the patient'"'"'s blood flowing through the blood chamber; detecting the intensity of the light at the first wavelength after it has passed through the extracorporeal blood chamber and the patient'"'"'s blood flowing therethrough; detecting the intensity of the light at the second wavelength after it passes through the extracorporeal blood chamber and the blood flowing therethrough; calculating a hematocrit value using the ratiometric model from at least the detected light intensity at the first wavelength and the detected light intensity at the second wavelength; and scaling the hematocrit value calculated by the ratiometric model by a scaling factor to result in a scaled hematocrit value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. For use with a hemodialysis system that draws blood from a patient, passes the drawn blood through extracorporeal tubing and through a dialyzer, and returns the dialyzed blood through extracorporeal tubing to the patient, a optical blood monitor associated with the hemodialysis system, the monitor comprising:
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a sensor assembly that monitors the patient'"'"'s blood flowing through the hemodialysis system, the sensor comprising; a blood chamber having an inlet and an outlet which are connected inline with extracorporeal tubing for the hemodialysis system, and a fluid passageway through which the drawn blood from the patient flows, a first photo emitter for emitting light at a first wavelength through the blood chamber and the drawn blood flowing through the blood chamber, a second photo emitter for emitting light at a second wavelength through the blood chamber and the drawn blood flowing through the blood chamber, and at least one photo detector for detecting the intensity of the light at each wavelength after it passes through the blood chamber and the drawn blood; a controller that comprises a ratiometric model that calculates an hematocrit value as a function of at least a detected value of light intensity at the first wavelength and a detected value of light intensity at the second wavelength, wherein the ratiometric model is calculated at least in part by testing the ratiometric model with whole blood from a supply of blood preserved in a first anticoagulant and measuring the hematocrit value of whole blood from the same supply of blood preserved in the first anticoagulant using an in vitro method, and calibrating the ratiometric model to the hematocrit value measured using the in vitro method, and further wherein the controller comprises means for scaling the hematocrit value calculated by the ratiometric model by a scaling factor to determine a hematocrit value that is output or displayed by the optical blood monitor. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20)
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Specification