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What do the oxygen saturation numbers mean?

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What do the oxygen saturation numbers mean?

Postby Jessica » Wed Feb 14, 2007 11:56 pm

The sleep clinic brought me this thing today that I put on my finger, and it measures my oxygen saturation. A pulse Oximeter.
I'm about to go to bed, and I just put it on my finger. The top number is labled %SpO2, and it says 100. The bottom number just has a picture of a heart by it, and it says 99.
I have to give it back tomorrow, and I'd just like to have some idea of what the numbers mean. Of course, I assume by the time I see them again, I'll be awake, and they will be good numbers, even if they weren't while I was sleeping, but still, if someone can explain, I'd appreciate it.
And I have another question. How in the WORLD does a thing on your finger know how much oxygen is in your bloodstream? I'm confused.
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Postby Vicki » Thu Feb 15, 2007 12:20 am

Hi Jessica!

Your pulse-ox., which I refer to as an "ET thingy", measures oxygen saturation (the %SpO2 number) and pulse rate (the heart). Normal %SpO2 is > 95%. Depending on where you read the definition, SpO2 stands for either Spot Oxygen Saturation or Saturation of Peripheral Oxygen.

Here is an excerpt taken from this site:


Oximetry measures the percentage of hemoglobin saturated with oxygen by passing specific wavelengths of light through the blood. In 1875 a German physiologist named Karl von Vierofdt demonstrated that the oxygen in his hand was consumed when a tourniquet was applied. This was done utilizing transmitted light waves, but the development of the pulse oximeter was still a long way off. In 1936 Karl Matthes developed the first ear saturation meter that used two wavelengths of light. This compensated for the variations in tissue absorption. This idea was improved upon in 1940 when Glen Millikin developed a lightweight oximeter to help the military solve their aviation hypoxia problem. The modern pulse oximeter was developed in 1972 by Takuo Aoyagi while he was working in Tokyo developing a noninvasive cardiac output measurement, using dye dilution and an ear densitometer. He noticed a correlation in the difference between unabsorbed infrared and red light and the oxygen saturation. This led to the clinical application of the pulse oximeter. It was not until 1980 that Nellcor produced the first commercial pulse oximeter that was reliable, robust, and affordable. In 1988 the use of a pulse oximeter during anesthesia and recovery became mandatory in
Australia. Since then, its use has become mandated in many areas from pre-hospital treatment to intensive care units.

Pulse Oximeter Definition
What is it?
A pulse oximeter consists of a computerized monitor and a probe that can be attached to the patient's finger, toe, nose, or earlobe. The monitoring unit displays a digital percentage readout of a calculated estimate of the patient's hemoglobin (Hgb) that is saturated with oxygen (SpO2.) A visual waveform indicator is displayed and an audible signal is emitted with each pulse beat, where the tone decreases with a corresponding decrease in saturation. Also displayed is a calculated heart rate. Alarms are available to alert the user to either a high or low saturation level or fast or slow pulse rate.

What does it do?
The device measures two types of hemoglobin: oxygenated and deoxygenated. Since two different substances are being measured, two frequencies of light are necessary. This is called spectrophotometry. The red frequency measures desaturated hemoglobin and the infrared measures oxygenated hemoglobin. If the oximeter measures the greatest absorbance in the red band, it will indicate low saturation. If the greatest absorbance is in the infrared band, it will indicate a high saturation.

How does it do it?
The pulse oximeter utilizes the two wavelengths of light to calculate the saturation of oxyhemoglobin. As a light is shone through the finger, it is picked up by a receiver. Some of the light is absorbed by the tissues, including arterial blood. As the artery fills with blood, the absorption increases; and as the artery empties, the absorption decreases. Since the pulsating blood is the only substance that is changing, the stable substances (skin and tissue) are eliminated from the calculation."

There is more of the actual O2 sat. calculation at the site if you are interested.

The pulse-ox. records O2 sat. and pulse rate the whole night and the results are downloaded as soon as it is returned. While many apnea patients show desaturations with a pulse-ox., many do not. Therefore, using a pulse-ox. soley to diagnose apnea is not acceptable.

Being defeated is often a temporary condition. Giving up is what makes it permanent.
Marilyn Vos Savant

That which does not kill you makes you stronger-Friedrich Nietzsche
Friedrich must of had apnea.
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