How to Get the Most Accurate Readings with a Pulse Oximeter

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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Nurse Becomes Patient in Traumatic Gym Injury-Catch this Train & Help Keith Carlson, BSN, RN, NC-BC

Our highly respected and compassionate colleague, Nurse Coach and Author Keith Carlson is recovering from a major traumatic injury.  And he has a long rehab ahead of him.  WE KNOW THIS!

Skip the story and jump on the train to help!

Don’t skip the story, tell us what happened!

Earlier in July, Keith was doing his usual workout at a local gym including cardio, weights, and resistance training.  He was deep into his usual process when he heard a sound and then instantaneously felt a searing pain in my left ankle as he fell to the floor.

…the metal anchor for the bungee cords had torn from the wall as I did my usual exercise, and this 18-inch piece of molded sheet metal flew at me with all of the pent up force of those six tensed rubber tubes. It guillotined the lateral aspect of my left lower leg just above the lateral malleolus.  -Keith Carlson

More from Keith about this. 

Extensive surgery followed and some kind but questionable care too.  (no nurse checked his pedal pulse for 48 hours post-op and the surgeon tried to force him to be discharged on a Sunday at 5pm, despite ongoing pain, dizziness, nausea, and a home completely unprepared for a disabled patient).  Makes me furious!

WE KNOW THIS stuff happens TOO!  UGH!

There’s a way we can help locally or nonlocally!

Meal Train to Help

Santa Fe locals can sign up to deliver meals, and non-locals can make donations or buy gift cards for Santa Fe restaurants or grocery stores.

This is a great idea to know about for others too, right?

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Calling all Nurses!  Would You Complete a Quick Survey re: The Impact of Workplace Violence & Emotional Exhaustion on the Profession?

Meet John Good, a doctoral candidate in business administration at The University of Wisconsin-Whitewater.

I want to understand these impacts to propose effective treatments that diminish the occurrence of workplace violence and emotional exhaustion within the nurse profession.

Please help John by completing this brief survey!

His dissertation research is focused on the impact of workplace violence and emotional exhaustion upon the nurse profession.

It is a quick way to provide your important insights to meaningful work!

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