Optimizing SpO
2
Measurement Performance
8-22 SpO
2
Monitoring
Optimizing SpO
2
Measurement Performance
Refer to this section on problem situations if you have difficulty getting a signal
or obtaining accurate measurements.
Distortion
Ambient light, motion, perfusion or incorrect sensor placement can affect the
accuracy of the derived measurements.
Arterial Blood Flow
The measurement depends on the pulsatile nature of blood flow in the arteries
and arterioles; with the following conditions arterial blood flow can be reduced
to a level at which accurate measurements cannot be made:
•shock
• hypothermia
• use of vasoconstrictive drugs
• anemia
Wavelength Absorption
The measurement also depends on the absorption of particular light wavelengths
by the oxyhemoglobin and reduced hemoglobin. If other substances are present
which absorb the same wavelengths, they will cause a falsely high, or falsely
low SpO
2
value to be measured. For example:
• carboxyhemoglobin
• methemoglobin
• methylene blue
• indocyanine green*
• indiocarmine*
*These chemicals are used in dye dilution cardiac output calculations.
Ambient Light
Very high levels of ambient light can also affect the measurement; an "SpO
2
Interference" message will appear on the display. The measurement quality can
be improved by covering the sensor with suitable opaque material.
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