Principles of Pulse Oximetry

A pulse oximeter is a medical device that assess a person's breathing by measuring blood oxygen levels. This device is usually attached to the finger, but can also be attached to the ear, foot or other places on the body.

Oxygen Saturation

• Oxygen travels through the blood stream attached to hemoglobin molecules. The bloods oxygen saturation refers to how much oxygen the blood is carrying as compared to the maximum the blood could carry. Oxygen saturation is also called SpO2.

Standard Oxygen Levels

• Keep in mind that oxygen levels do vary with age, altitude, and whether or not a patient is undergoing oxygen therapy. The average young, healthy individual should have levels between 95 to 99 percent.

How It Works

• Oximeters today use two light-emitting diodes (LED's). One of the diodes emits a red light that you can see, and the other emits an infrared light that you can't see. These two wavelengths are used to determine the color of blood in the arteries, which indicates the blood oxygen levels. Because there is tissue in the fingers that add color to a reading, the oximeter uses the pulse of the heartbeat to pinpoint the exact color of the blood, hence the term "pulse oximetry."

Ideal Conditions

• Since oximeters depend on a signal in order to function, it is important to make sure that there is a strong pulse. If the pulse is too weak, the oximeter might not function. Cold hands and feet can result in a weak pulse. Some oximeters give you the ability to measure the strength of a signal, which is important to check to ensure accurate results.

Cautions

• Keep in mind, oxygen levels don't tell everything about a person's breathing. For example, carbon dioxide levels are also important. Someone might be getting enough oxygen, but might not be getting rid of enough carbon dioxide. At a minimum, it is also necessary to record respiratory rate, and to determine whether or not the patient is on oxygen therapy.