How to Get the Most Accurate Readings with a Pulse Oximeter

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by Mandy Johnson

How to Use a Finger Pulse Oximeter

A pulse oximeter is an efficient tool that has helped a lot of medical healthcare teams in terms of patient assessment over the years. This medical device is used to measure the heart rate and the blood oxygen levels, which represents the oxygen saturation percentage.

A pulse oximeter works by shedding light through the skin where blood vessels are dominant. A reading of close to 100 percent shows a high oxygen saturation, which is a good thing since this means that the red blood cells are jam-packed with oxygen coming from the lungs.

Understanding oxygen saturation

To fully understand the concept of pulse oximetry, it’s best to grasp the meaning of oxygen saturation, which is referred to as SpO2. Considering that oxygen is carried throughout the blood by attaching itself to the red blood cells, oxygen saturation is simply the measure of how much oxygen there is in the blood based on the maximum amount it could carry.

To put it simply, a hemoglobin molecule is able to carry four molecules of oxygen at maximum, so if an SpO2 sensor detects that it is carrying three oxygen molecules, that red blood cell is carrying 75% or ¾ of the maximum oxygen amount it could carry.

How pulse oximetry works

A pulse oximetry sensor works by emitting light with both red and infrared LEDs through a translucent site in the body where there is good blood flow. Common sites that provide accurate pulse oximeter results include the finger, toe, and lobe of the ear. Meanwhile, the palm of the hand or the foot are good sites for infants.

The results of pulse oximetry depend on the light absorption characteristics of both oxygenated and deoxygenated hemoglobin. Basically, oxygenated hemoglobin is able to absorb more infrared light and let more red light to pass through. In the case of deoxygenated hemoglobin, it’s the other way around.

Using a finger pulse oximeter

For members of the healthcare team, it is important to understand the concept of pulse oximetry and to actually know how to operate the medical device.

After turning the pulse oximeter on, place the SpO2 sensor, the part that looks and works like a clothespin, on any finger. Remember to keep the sensor screen above the nail. Once it is in place, the device will then acquire a signal, which could take up to 10 seconds or more. While you are waiting, check the display screen for the heart rate, which could be indicated by a heart icon or a pulsing light. Meanwhile, you can take note of the oxygen saturation percentage, which is indicated by an “SpO2” symbol.

You can leave the pulse oximetry sensor in place if continuous monitoring is required. Just make sure to check for pressure sores every now and then, as this could happen especially when the device is left on the finger for too long. To avoid this, move the sensor every two to four hours at the least.

Errors in pulse oximetry

While an SpO2 pulse oximeter provides reliable data, there is no guarantee that it is error-proof. It may provide inaccurate results in case of excessive movement or when it is done in an environment where there is ambient light, as well as in patients with nail polish on their fingers. It’s also important to note that a pulse oximeter cannot differentiate between the different hemoglobin forms. For instance, carboxyhemoglobin is already 90% oxygenated and 10% desaturated, which could lead to overestimated results.

A seemingly simple device such as the pulse oximeter can ultimately save a life. In case of a low oxygen saturation measurement, which measures below the normal range of 95 to 100 percent, look for visible signs of respiratory distress and seek medical help right away.

Author Bio:  Mandy Johnson specializes in Internal Medicine. She has been in the medical field for 8 years now. Aside from having patients, she also enjoys writing medical stuff that helps people to easily understand the nature of her job. 


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