Understanding Pulse Oximetry
M4735A Heartstream XL Defibrillator/Monitor 5-3
5
Understanding Pulse Oximetry
A pulse oximetry sensor sends light through patient tissue to a receiver on the
other side of the sensor. As Figure 5-1 shows, light emitting diodes transmit
red and infrared light through peripheral areas of the body, such as a finger.
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A photodector positioned opposite the light emitting diodes compares light
absorption before and after pulsation. The amount of light getting through
reflects the blood flow in the arterioles. This measurement of light absorption
during pulsation is translated into an oxygen saturation percentage and an
SpO
2
value is displayed.
For accurate SpO
2
measurements, the following conditions must apply:
l
The patient must have perfusion in that extremity.
l
The light emitter and the photodetector must be directly opposite each
other.
l
All of the light from the emitter must pass through the patient’s tissue.
l
The sensor site should be free of vibration and excessive motion.
l
Power cables should be kept away from the sensor cable and connec-
tor.
Light Emitting
Diodes
Photodetector
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