Finger pulse oximeters are mainly useful to reassure you that your oxygenation is OK (90+%), or that you should don oxygen or troubleshoot the situation (85% or below). The fact that their readings are often inaccurate and misleading does not mean that they are useless!
What is oximetry?
Oximetry is a procedure for measuring the concentration of oxygen in the blood. The test is used in the evaluation of various medical conditions that affect the function of the heart and lungs.
How is oximetry done?
This is done using an oximeter, a photoelectric device specially designed for this purpose. A reusable probe can be placed on the finger or a single use tape probe is placed on the earlobe or finger.
What are pulse oximeters?
The oximeters most commonly used today are called pulse oximeters because they respond only to pulsations, such as those in pulsating capillaries of the area tested.
How common are oximeters?
Oximeters are now a virtual fixture in intensive care units, pulmonary units and elsewhere in hospitals and health care facilities.
How does a pulse oximeter function?
A pulse oximeter works by passing a beam of red and infrared light through a pulsating capillary bed. The ratio of red to infrared blood light transmitted gives a measure of the oxygen saturation of the blood. The oximeter works on the principle that the oxygenated blood is a brighter color of red than the deoxygenated blood, which is more blue-purple. First, the oximeter measures the sum of the intensity of both shades of red, representing the fractions of the blood with and without oxygen. The oximeter detects the pulse, and then subtracts the intensity of color detected when the pulse is absent. The remaining intensity of color represents only the oxygenated red blood. This is displayed on the electronic screen as a percentage of oxygen saturation in the blood.
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Are there other types of oximetry?
Yes. Oximetry can also be done on blood that is within the heart (intracardiac oximetry) or on whole blood that has been removed from the body. More recently, using a similar technology to oximetry, carbon dioxide levels can be measured at the skin as well.