Pulse Oximeter : Working, Readings

A small clamp-like device is mounted on an earlobe, finger, or toe during a pulse oximetry reading. Tiny beams of light flowing through the blood are used to determine the amount of oxygen in the finger. It accomplishes this by detecting differences in light absorption in both oxygenated and deoxygenated blood. This is a simple technique.

Pulse oximeter

As a result, the pulse oximeter will show both the oxygen saturation and heart rate.


How does an oximeter work?

                                       Pulse wave signal

(old model oximeter) The probe is attached to the finger and detects the flow of blood through it. On the computer, this is seen as a pulse wave.


To demonstrate that a pulse is being detected a pulse wave must be present.


The patient in this illustration has a heart rate of 72 beats per minute and oxygen saturation of 98 percent.


The pulse rate is referred to as the heart rate on this panel.


What is this red light for?

Lights in oximeter

Light-emitting diodes (LEDs) in all pulse oximeter probes (finger or ear) shine two forms of red light through the tissue.  The sensor on the other side of the tissue picks up the light that is transmitted through the tissues.


The oximeter will measure the amount of hemoglobin in pulsatile blood (arterial) and thus the arterial blood's SpO2 in the peripheral circulation.


Pulse oximetry readings


In most cases, pulse oximetry is a fairly accurate test. This is especially true when using high-quality equipment, such as that found in most medical offices and hospitals. It consistently generates results that are within 2% of what they really are.

If your reading was 82 percent, your true oxygen saturation level may be between 80 and 84 percent. However, the waveform's accuracy, as well as the individual's assessment, must be considered. The accuracy can be affected by movement, temperature, and nail polish.

                                    Readings in oximeter

In most cases, more than 89 percent of the blood should be carrying oxygen. This is the amount of oxygen saturation that your cells — and your whole body — need to remain healthy. Although having an oxygen saturation below this level for a short time is unlikely to cause harm, low oxygen saturation levels that are repetitive or constant can be harmful.

An oxygen saturation level of 95% is considered normal for most healthy people. Hypoxemia, or a lack of oxygen reaching body tissues, is indicated by a degree of 92 percent.

Source: Healthline, WHO.

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