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A pulse oximeter is a medical device that indirectly measures the amount of oxygen in a patient's blood. It is often attached to a medical monitor so staff can directly read a patient's oxygenation at all times.
By far, the most common monitor measures hemoglobin saturation. Typically it has a pair of small light-emitting diodes against a photodiode on a probe clipped to a translucent part of the patient's body (usually a fingertip or an earlobe). One LED is red, with wavelength of 660 nm, the other is infrared, 910 nm. Absorptions on each wavelength differs significantly for the oxyhemoglobin and its deoxygenated form, therefore from the difference of the absorption of the red and infrared light the oxy/deoxyhemoglobin ratio can be calculated. As the amount of blood in the capillaries depends on the actual blood pressure, which varies around the heart pulse cycle, the heartbeat rate can be measured as well.
A blood-oxygen monitor customarily measures percent of normal. Acceptable normal ranges are from 95 to 100 percent. For a patient breathing room air, at not far above sea level, an estimate of arterial pO2 can be made from the blood-oxygen monitor SpO2 reading.
The monitored signal bounces in time with the heart beat because the blood vessels expand and contract with the heartbeat. Some monitors also measure heart rate. Modern oximeters can clip onto the finger of a patient and use optical properties of light going through a nail to determine the amounts of these chemicals. Prior to the oximeter's invention, many complicated blood tests needed to be performed.
Blood oxygen monitors are of critical importance in emergency medicine and are also very useful for patients with respiratory or cardiac problems, as well as pilots operating in a non-pressurized aircraft above 10,000 feet (12,500 feet in the US), where supplemental oxygen is required.
The latest generation pulse oximeters use advanced digital signal processing to make accurate measurements in clinical conditions that were otherwise impossible. These include situations of patient motion, low perfusion, bright ambient light, and electrical interference.
It also should be noted that some saturation level measurement devices may not distinguish aspired carbon monoxide from oxygen, e.g., from a fire in an apartment, which must be taken in account during diagnosing a patient in emergency rescue. A CO-oximeter measures absorption at more different wavelengths to distinguish CO from O2 and determine the blood oxygen saturation more reliably. In 2005 Masimo Corporation introduced the first FDA-approved pulse oximeter to monitor carbon monoxide levels noninvasively.
See also
External links
- Pulse Oximeter Supplier to Nonprofit Clinics and Hospitals
- How Pulse Oximeter Works
"Pulse oximeter"