Absolute blood volume estimation device and method
Absolute blood volume in dialysis patients is a useful patient attribute to know for dialysis treatment, diagnosis, adjustments, etc. In some cases, it is difficult or impossible to directly determine absolute blood volume. Estimating absolute blood volume may be used to overcome the inability to directly determine the absolute blood volume. Estimating absolute blood volume may include obtaining a series of measurements of hemoconcentration of a patient over a time period, and estimating parameters for a physiological model based on the series of measurements. The absolute blood volume of the patient may be determined using the physiological model.
1. A method for estimating absolute blood volume at a dialysis machine, the method comprising:
injecting, using a pump, a predetermined volume of indicator liquid into a blood stream of a patient;
obtaining, via a sensor, a series of measurements of hemoconcentration of at least one blood characteristic of the patient over a time period, the series of measurements including a hemoconcentration at a dilution test time during the time period, and the series of measurements of hemoconcentration based on blood volume compared to the predetermined volume of indicator liquid;
estimating parameters for a physiological model based on the series of measurements, the parameters including the hemoconcentration at the dilution test time, a volume of a first compartment and a volume of a second compartment at the dilution test time and at an dilution injection time of the time period;
determining an absolute blood volume of the patient at the dilution test time using the physiological model and the series of measurements of hemoconcentration; and
outputting the absolute blood volume on a display portion of the dialysis machine.
2. The method of claim 1 , further comprising, prescribing, at the dialysis machine, a dialysis treatment action for the patient based on the absolute blood volume at the dilution test time.
3. The method of claim 1 , further comprising, modifying, at the dialysis machine, a dialysis treatment action for the patient automatically based on the absolute blood volume.
4. The method of claim 1 , wherein the dilution test time is ten minutes after the dilution injection time, and wherein the injection occurs at the dilution injection time.
5. The method of claim 1 , wherein the time period includes a period before the dilution injection time and the series of measurements include measurements taken during the period before the dilution injection time for a baseline.
6. The method of claim 1 , wherein the estimated parameters are unique to the patient at the dilution injection time.
7. The method of claim 1 , wherein the estimated parameters include a blood exchange between the first and second compartments, a fluid exchange with interstitial space, and a time delay.
8. The method of claim 1 , wherein estimating the parameters includes fitting the physiological model to the series of measurements.
9. The method of claim 8 , wherein fitting the physiological model to the series of measurements includes performing a nonlinear least squares fit and minimizing a root-mean-square error between the series of measurements and blood volume estimates resulting from the physiological model.
10. The method of claim 1 , wherein estimating the parameters include using a patient-specific attribute including gender, age, weight, ethnicity, or comorbidity.
11. The method of claim 1 , wherein the at least one blood characteristic includes at least one of a relative blood volume, a blood volume monitor (BVM) measurement, a hematocrit measurement, or a hemoconcentration measurement.