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What is SpO2, pulse oximetery and how do pulse oximeters work?
Pulse oximetry measures SpO2 which is very closely correlated to the blood saturated oxygen content in the arteries. Pluse oximeters measure continuously and non-invasively meaning that they can measure and produce results all external to the body - no insertions are needed. It can be very important to know your SPO2 in situations where someone has a compromised heart lung system and might suffer from something like COPD and need oxygen therapy.
Standard Pulse oximetry is based on the light absorbing properties of haemoglobin which is the molecule that carries oxygen in the blood. The oximeter generates red and infrared light and it also has a light detector. In a handheld device, a sensor (also called a probe) is placed around a hand or foot and two light-emitting diodes send red and infrared frequency light through the skin. In the case of a fingertip oximeter, or a fingertip probe, a finger is inserted within the center of the unit.
The amount of light that passes through to the photodetector on the other side is analyzed. There are two major signals that are received. One is where there is a surge of blood that occurs with each heartbeat which creates an increase of arterial blood volume. The other signal received is during periods betweem haertbeats.
SpO2 is estimated from the amount of light absorbed during periods of heartbearts when the amount of oxygen is highest and the blood volume is the highest. The greater the amount of light absorbed, the higher the amount of SpO2 calculated. The pulse or heart rate is measured by determining the time between the high levels of oxygen (ie., when there is a heartbeat) and when the oxygen level drops.
Note that pulse oximeter do not need to be calibrated (most cannot be adjusted so they are either within their specifications or not). Most units are either +/-2 or +/- 3 percent in accuracy. This means that is the "true" value is 95 % and the oximeter is +/- 3%, it reading may range from 92% to 98% and still be within specification. It is most important to get the most accuarate unit +/- 2% if you are on oxygen therapy or your oxygen levels average below 93%. Consult your physician but 88% is generally considered a critically low level.
Also note that there are other methods of determining SpO2 such as using a reflectance method. This allows SpO2 to be measured during situations where there may be blood vessel disease where there is low flow in the fingers, for example. Reflectance can be used to measure on the forehead.
Southeastern Medical Supply has a variety of pulse oximeters at various prices and quality levels. Look at specifications to get detailed information so you can determine which unit is right for you. All of our pulse oximeters are FDA registered.
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