The pulse oximeter is a photoelectric instrument for measuring oxygen saturation of blood.
A pulse oximeter measures the amount of oxygen present in blood by registering pulsations within an arteriolar bed (an area between arteries and capillaries). It is a noninvasive method widely used in hospitals on newborns, persons with pulmonary disorders, and individuals undergoing pulmonary and cardiac procedures. Oxygen levels can be estimated during exercise , surgery, or other medical procedures, or while a person is asleep.
The oximeter consists of a light-emitting diode (LED), a photodetector probe containing a permanent or disposable sensor, alarms for pulse rate and oxygen levels, a display screen, and cables. The device works by emitting beams of red and infrared light that are passed through a pulsating arteriolar bed. Sensors detect the amount of light absorbed by oxyhemoglobin and deoxyhemoglobin in the red blood cells. The ratio of red to infrared light measured by the photodetector indicates the amount of oxygen present in the blood. The sensor is attached to the body over the arteriolar area in the ear, the fingertip, the big toe, or across the bridge of the nose. Clip sensors can be used on fingers or the earlobe.
The pulse oximeter is widely used in most hospitals and in research laboratories that study pulmonary function. Oximeters are used in hospital settings such as intensive care units, pulmonary units, and in health care centers. Portable hand-held devices are available, and are used to spot check patients and for in-home use under the supervision of a physician.
Several steps can be taken to enhance accurate readings. If possible, the patient should not smoke 24 hours prior to pulse oximetry. Fingernail polish should be removed if the oximeter will be attached to the finger. For people with poor circulation, hands should be slowly warmed with warm towels before attaching the oximeter. Abnormally high or low temperatures, as well as reduced hemoglobin, can influence the amount of oxygen adhering to the hemoglobin within the red blood cells, altering the reading. The sensor should be wrapped securely around the finger to prevent outside light from interfering with the reading, which could render it invalid. The device must not be used near flammable anesthetics.
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L. Fleming Fallon, Jr. MD, DrPH