Pulse Oximetry: Normal Values

The great benefit of these finger pulse oximeters is that they provide an instantaneous and continuous monitoring of oxygenation, and this in turn provides an early warning sign of problems such as hypoxia before other signs such as cyanosis, tachycardia or bradycardia appear.

This means that with these medical monitoring devices there has been a substantial reduction in the frequency of oxygenation measuring in laboratories and clinics that provide blood gas analysis.

Pulse oximeters provide a spectro-photometric assessment of hemoglobin oxygenation (SpO2) by measuring the light transmitted through a capillary bed, synchronized with the pulse. The detection system consists of light emitting diodes (LED) of a single wavelength, photo detectors and microprocessors.

Pulse oximeters are based on the principle of differential absorption of light to determine the percentage of oxygen saturation of hemoglobin in arterial blood (SpO2, this value is called SaO2 when measured from a sample of blood ).

Each pulse of the arterial blood makes the capillary bed expand and relax. The resulting cyclical variations in the length of the path of the transmitted light allow the device to distinguish between hemoglobin saturation in arterial blood (pulse) and the venous blood and tissue components because there is no pulse of the surrounding tissue and the pulse of the venous blood is negligible.

Pulse oximetry normal values:

These will have slight variations at different times and also depending on the altitude. Saturation in a healthy person at sea level varies from 96 to 100%.

It is normal for oxygen saturation to decrease as we climb to higher altitudes. For example at 2200 meters (7,218 feet) above sea level, a healthy young person once he or she has adjusted to this altitude will go from 91% to 94%.

In general terms a saturation that is greater or equal to 90% is considered normal.

As a general guide, supplementary oxygen is required i when saturation is below 88%.
Although each disease demands its own precise indications.

Definition of Medical Terms From This Article

Arterial Blood: Refers to the blood after being oxygenized in the lungs and passes into the left atrium and ventricle of the heart and from there it spread through the arteries throughout the body. Oxygenated blood, found in the pulmonary veins, the left chambers of the heart, and the systemic arteries.

Arterial Blood Flow: The pressure of the blood in the arterial system, which depends on the heart's pumping pressure, the resistance of the arterial walls, elasticity of vessels, the blood volume, and its viscosity.

Bradycardia: Slowness of the heartbeat, as evidenced by slowing of the pulse rate to less than 60.

Capillary Bed: A dense network of tiny blood vessels that enables blood to fill a tissue or organ.

Cyanosis: Cyanosis is a physical sign causing bluish discoloration of the skin and mucous membranes. Cyanosis is caused by a lack of oxygen in the blood. Cyanosis is associated with cold temperatures, heart failure, lung diseases, and smothering. It is seen in infants at birth as a result of heart defects, respiratory distress syndrome, or lung and breathing problems.

Hemoglobin: The red respiratory protein of red blood cells that transports oxygen as oxyhemoglobin from the lungs to the tissues, where the oxygen is readily released and the oxyhemoglobin becomes hemoglobin.

Hypoxia: Insufficient oxygen supply to tissues in the body; symptoms include hypertension, dizziness, peripheral vasoconstriction, tachycardia, mental confusion, and other manifestations.

Oxygenation: The act or process of adding oxygen. The result of having oxygen added.

Tachycardia: A rapid heart rate, especially one above 100 beats per minute in an adult. Also called tachyrhythmia.

Venous Blood: Blood that has passed through the capillaries of various tissues other than the lungs, is found in the veins, in the right chambers of the heart, and in pulmonary arteries, and is usually dark red as a result of a lower content of oxygen.

Glossary Terms References:
Mosby's Medical Dictionary, 8th edition. © 2009, Elsevier.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company.