Oxygen saturation (SpO2 ) and pulse rate can be displayed as bars or waves:

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How it works:

A pulse oximeter works by passing a beam of red and infrared light through a pulsating capillary bed. The ratio of red to infrared blood light transmitted gives a measure of the oxygen saturation of the blood. The oximeter works on the principle that the oxygenated blood is a brighter color of red than the deoxygenated blood, which is more blue-purple.

First, the oximeter measures the sum of the intensity of both shades of red, representing the fractions of the blood with and without oxygen. The oximeter detects the pulse, and then subtracts the intensity of color detected when the pulse is absent.

The remaining intensity of color represents only the oxygenated red blood. This is displayed on the electronic screen as a percentage of oxygen saturation in the blood [Source:  webmd.com].

How To Read a Pulse Oximeter:

Heart and Pulse Rate

A portable pulse oximeter is a device that clips onto your finger and reads your heart rate as well as the percent of oxygen in your blood. It was developed as a way to detect hypoxia (a condition caused by insufficient oxygen). The hemoglobin in your blood bonds to oxygen and carries it through your circulatory system to your body’s cells. A pulse oximeter works by emitting an infrared light that shines through your body’s tissue to a photosensor on the other side. The infrared light is able to detect the amount of hemoglobin that is saturated with (or carrying) oxygen. The pulse oximeter will display a number that indicates the percent of hemoglobin that is saturated with oxygen. A pulse oximeter reading (denoted by SpO2) in the high 90s (i.e. 96%-99%) is considered normal. Here’s how to read a pulse oximeter.

·       Clip the pulse oximeter on. The pulse oximeter must be clipped, like a clothespin, onto a part of your body where light can shine through the blood flowing through your arteries. This includes your finger (where the pulse oximeter is most commonly placed on adults), toe, earlobe or across the bridge of your nose. Because pulse oximetry so often occurs on the finger, these devices are also commonly called a finger pulse oximeter.


Some common scenarios that result in an erroneous reading include:

Nail polish, if the pulse oximeter is clipped on a finger.
·        Excessive movement by the patient
·        Hypothermia or a cold injury to the extremities
·        Anemia (not enough iron in the blood)
·        Carbon monoxide poisoning
·        Certain types of seizures
·        Shock (hypoperfusion) associated with blood loss or poor perfusion
·       Remain still. As noted above, excessive movement can result in the pulse oximeter providing you with an inaccurate reading. Try to remain relatively still while the pulse oximeter is taking its reading.