Pulse oximetry is a noninvasive method for monitoring a person's oxygen saturation. Peripheral oxygen saturation (SpO2) readings are typically within 2% accuracy (within 4% accuracy in the worst 5% of cases) of the more desirable (and invasive) reading of arterial oxygen saturation (SaO2) from arterial blood gas analysis. But the two are correlated well enough that the safe, convenient, noninvasive, inexpensive pulse oximetry method is valuable for measuring oxygen saturation in clinical use.
The most common approach is transmissive pulse oximetry
. In this approach, a sensor device is placed on a thin part of the patient's body, usually a fingertip or earlobe, or an infant's foot. Fingertips and earlobes have higher blood flow rates than other tissues, which facilitates heat transfer. The device passes two wavelengths of light through the body part to a photodetector. It measures the changing absorbance at each of the wavelengths, allowing it to determine the absorbances due to the pulsing arterial blood alone, excluding venous blood, skin, bone, muscle, fat, and (in most cases) nail polish.
Pulse oximetry is particularly convenient for noninvasive continuous measurement of blood oxygen saturation. It is useful in any setting where a patient's oxygenation is unstable—including intensive care, operating, recovery, emergency, and hospital ward settings—for assessment of any patient's oxygenation and to determine the effectiveness of or need for supplemental oxygen.
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Adapted from Wikipedia, the free encyclopedia. Internet. Accessed on May 4, 2020. Available at https://en.wikipedia.org/wiki/Pulse_oximetry