How a Pulse Oximeter Works

Pulse oximeters use red and infrared light to detect oxygen in the blood stream.  The hemoglobin which carries the oxygen absorbs more infrared light but allows more red light to pass through.  Conversely, hemoglobin without much oxygen absorbs more red light and allows more infrared through.

A pulse oximeter is usually placed somewhere on the body where there is good blood flow.  Usually, most patients will have one placed on their finger, toe or ear lobe for the most concise results.  Infants, however, have different places where it is more suitable.  Usually these sites are the foot or palm of the hand or the big toe and thumb.

Once the information is transmitted to the machine, the ratios of red to infrared light are calculated and compared to a model table.  Typically, a good reading ranges between 90 - 100 saturation.

Conventional pulse oximeters accuracy suffers when there is movement  and or  poor blood circulation  and makes it difficult to depend on when making medical decisions. Arterial blood gas tests done by taking blood directly from an artery have been and continue to be  the gold standard to validate  pulse oximeter readings.  Also available on the market are the “Next Generation” pulse oximeters.  Their technology has significantly improved the ability to read through motion and low perfusion issues thereby making pulse oximetry more dependable to base medical decisions on.