Robust fractional saturation determination
The present disclosure describes the derivation and measurement of a fractional oxygen saturation measurement. In one embodiment, a system includes an optical sensor and a processor. The optical sensor can emit light of multiple wavelengths directed at a measurement site of tissue of a patient, detect the light after attenuation by the tissue, and produce a signal representative of the detected light after attenuation. The processor can receive the signal representative of the detected light after attenuation and determine, using the signal, a fractional oxygen saturation measurement based on two or more different measures of fractional oxygen saturation.
1. A patient monitoring system comprising:
an optical sensor configured to emit light of a plurality of wavelengths directed at a measurement site of tissue of a patient and detect the light after attenuation by the measurement site to produce a signal representative of the light after attenuation; and
a patient monitor comprising:
one or more hardware processors configured to:
determine a methemoglobin measurement and a carboxyhemoglobin measurement from the signal,
determine that the methemoglobin measurement is indicative of a low methemoglobin condition, and
in response to determining that the methemoglobin measurement is indicative of the low methemoglobin condition, change the carboxyhemoglobin measurement to a weighted carboxyhemoglobin measurement that is correlated to the carboxyhemoglobin measurement; and
a display configured to display a parameter value responsive to the carboxyhemoglobin measurement.
2. The patient monitoring system of claim 1 , wherein the weighted carboxyhemoglobin measurement is weighted according to the methemoglobin measurement.
3. The patient monitoring system of claim 1 , wherein when the methemoglobin measurement is within a range, the weighted carboxyhemoglobin measurement is weighted so that a weighting of the carboxyhemoglobin measurement increases as the methemoglobin measurement increases.
4. The patient monitoring system of claim 3 , wherein the range extends from a low value to a high value, the high value being between 7% and 8%.
5. The patient monitoring system of claim 3 , wherein when the methemoglobin measurement is within the range, the weighting varies with the methemoglobin measurement at least in part according to an exponential function.
6. The patient monitoring system of claim 3 , wherein when the methemoglobin measurement is within the range, the weighting varies with the methemoglobin measurement at least in part according to a linear function.
7. The patient monitoring system of claim 1 , wherein the parameter value is indicative of a fractional oxygen saturation.
8. The patient monitoring system of claim 1 , wherein the parameter value equals the carboxyhemoglobin measurement.
9. The patient monitoring system of claim 1 , wherein the one or more hardware processors is configured to:
determine that the methemoglobin measurement is unreliable, and
in response to determining that the methemoglobin measurement is unreliable, change the carboxyhemoglobin measurement to a default carboxyhemoglobin value.
10. The patient monitoring system of claim 9 , wherein the one or more hardware processors is configured to:
determine that the methemoglobin measurement is indicative of the low methemoglobin condition from a comparison of the methemoglobin measurement to a first threshold, and
determine that the methemoglobin measurement is unreliable from a comparison of the methemoglobin measurement to a second threshold different from the first threshold.
11. The patient monitoring system of claim 10 , wherein the first threshold is 1%.
12. The patient monitoring system of claim 10 , wherein the second threshold is 2.2%.
13. The patient monitoring system of claim 12 , wherein the default carboxyhemoglobin value is 0.9%.
14. The patient monitoring system of claim 1 , wherein the signal is representative of the light of three or more wavelengths after attenuation, and the one or more hardware processors is configured to determine the methemoglobin measurement and the carboxyhemoglobin measurement from the light of three or more wavelengths after attenuation.
15. The patient monitoring system of claim 1 , wherein the signal is representative of the light of five or more wavelengths after attenuation, and the one or more hardware processors is configured to determine the methemoglobin measurement and the carboxyhemoglobin measurement from the light of five or more wavelengths after attenuation.
16. A method of patient monitoring, the method comprising:
emitting light of a plurality of wavelengths directed at a measurement site of tissue of a patient;
detecting the light after attenuation by the measurement site to produce a signal representative of the light after attenuation;
determining, with one or more hardware processors, a first methemoglobin measurement and a first carboxyhemoglobin measurement from the signal;
determining, with the one or more hardware processors, that the first methemoglobin measurement is indicative of a low methemoglobin condition;
in response to determining that the first methemoglobin measurement is indicative of the low methemoglobin condition, changing, with the one or more hardware processors, the first carboxyhemoglobin measurement to a weighted carboxyhemoglobin measurement that is correlated to the first carboxyhemoglobin measurement; and
displaying, with a display, a first parameter value responsive to the first carboxyhemoglobin measurement.
17. The method of claim 16 , wherein the weighted carboxyhemoglobin measurement is weighted according to the first methemoglobin measurement.
18. The method of claim 16 , wherein when the first methemoglobin measurement is within a range, the weighted carboxyhemoglobin measurement is weighted so that a weighting of the first carboxyhemoglobin measurement increases as the first methemoglobin measurement increases.
19. The method of claim 16 , further comprising:
determining, with the one or more hardware processors, a second methemoglobin measurement and a second carboxyhemoglobin measurement from the signal;
determining, with the one or more hardware processors, that the second methemoglobin measurement is unreliable;
in response to determining that the second methemoglobin measurement is unreliable, changing, with the one or more hardware processors, the second carboxyhemoglobin measurement to a default carboxyhemoglobin value; and
displaying, with the display, a second parameter value responsive to the second carboxyhemoglobin measurement.
20. The method of claim 16 , wherein the first parameter value is indicative of a fractional oxygen saturation.