Technologies That Allow for the Measurement of Oxygen Saturation

Oxygen saturation is the amount of oxygen carried in the blood by the hemoglobin in red blood cells. The normal saturation range is 95 to 100 percent; however, a person will typically only reach 100 percent if supplemental oxygen is used. Medical professionals can measure oxygen saturation in two ways -- a pulse oximeter and an ABG test.

Pulse Oximeter

• A pulse oximeter is a device or probe that is placed on the finger, earlobe or nose to measure the blood that is carrying oxygen.

How It Works

• The pulse oximeter contains two beams of light -- one you can see (a red light) and one you can't (infrared). According to Turner Medical, the technology of a pulse oximeter uses "the light source characteristics of hemoglobin and the pulsating nature of blood flow in the arteries to aid in determining the oxygenation status in the body." Additionally, according to Oximetery.org, "Oxygenated hemoglobin absorbs more infrared light and allows more red light to pass through." Because of this, the pulse oximeter can detect the oxygenated arterial blood (which is bright red) with every heartbeat, because there is a minute increase in the volume of blood flowing past the measurement site and, subsequently, an increase in the oxygen-rich hemoglobin that flows through as well.

ABG

• An ABG, or arterial blood gas, test is more comprehensive. It not only measures oxygen saturation (also called O2 Sat) but other elements as well, such as partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2) pH of blood and bicarbonate (the buffer that prevents the pH from becoming too acidic or basic). Technicians draw blood for the ABG from an artery, because it is oxygen-rich, which makes the ABG test more invasive than the pulse oximetry.

Why It's Done

• An ABG test checks for not just oxygenation of blood but signs of other medical conditions, too. Examples are breathing problems and lung diseases, like asthma and chronic obstructive pulmonary disease. Additionally, when a patient receives oxygen in the hospital or clinical setting, the test will show if the amount of oxygen is correctd. The ABG test also measures the acid-base level in the blood to determine if you have any acid-base imbalances, such as respiratory or metabolic acidosis (higher than normal acid levels) or even respiratory or metabolic alkalosis (higher than normal base levels).