Understanding Anesthesiology - The Global Regional Anesthesia ...

Pulse oximeter
The oxygen saturation monitor non-invasively measures the oxygen saturation of hemoglobin
in the patient’s arterial blood. It is also known as a pulse oximeter.
The pulse-ox is placed on a finger, toe or earlobe. Two different wavelengths of light (one
red, one infrared) are passed through the patient’s tissue from one side of the pulse-oximeter
to a photodetector on the other side. Absorption of light at these wavelengths differs significantly
between oxyhemoglobin and its deoxygenated form. Accordingly, the percentage of
oxygenated hemoglobin can be calculated from the ratio of the absorption of these two wavelengths
of light. By searching for a pulsatile signal, the device can measure the saturation in
arterial (not venous) blood.
There are many factors that can affect the ability of the pulse-oximeter to give an accurate
reading. Good peripheral blood flow is required which can be impeded in a cold or shocked
patient. Measurements can be erroneous when nail polish is used as well as in the presence
of carbon monoxide, cyanide and methemoglobin.
Related Glossary Terms
Hypoxemia, Oxygen saturation, Oxyhemoglobin dissociation curve, Shock
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Chapter 2 - Anesthetic Equipment and Monitoring