Definition of Oxygen Saturation

oxygen saturationOxygen saturation – The percentage of hemoglobin molecules in the blood that are bound to oxygen molecules.Normal oxygen saturation of the arterial blood is 96 to 98 percent.

Saturation significantly below normal, for instance 88 percent, indicates respiratory failure and may be lifethreatening.

Oxygen saturation is an essential measurement for assessing cardiovascular and pulmonary effectiveness. Inadequate oxygen saturation in the blood is hypoxemia.


The primary method for measuring oxygen saturation is pulse oximetry, which is painless and noninvasive. The pulse oximeter consists of two components, an emitter and a tiny computer chip. The emitter is a small device that fits over the fingertip or on the ear lobe. It projects beams of red and infrared light, which pass through the tissue to a sensor on the other side.

The volume of blood in the tissue at systole (peak contraction of the heart) is greater, resulting in more light being absorbed than with the lesser volume of blood in the tissue at diastole (relaxation of the heart). The oximeter’s computer chip measures this difference and uses it to mathematically calculate the percentage of oxygen the hemoglobin carries.


How did you like this article?

Page last reviewed:

About Us