How a Pulse Oximeter Works

This article was reviewed by Senior Director of Community Engagement and COPD360social Community Manager, Bill Clark, as well as certified staff Respiratory Therapists on January 23, 2020.

Dear COPD Coach, My husband has been diagnosed with COPD but has not yet had pulmonary function tests to determine the type/severity. We purchased a pulse oximeter to monitor his 02 levels (he was sent home from the hospital on 4 liters but is now reduced to 2). My question is, do you take the first reading that comes up when the pulse oximeter is put on or do you wait 15 seconds and use that reading? Also, I would like to say this is one of the most informative websites I have found on COPD and I certainly appreciate the support it provides.

—Curious about Pulmonary Function Testing

Dear Curious, A pulse oximeter can be a very useful tool for a COPD patient, providing you use it correctly and realize it has limitations.

The pulse oximeter measures two distinct things: The first number that comes up is most often the pulse rate. Usually this number is marked by a small heart. The second number that comes up is the level of oxygen in the blood. Both numbers are needed to assess your present levels.

At this point, it is important to discuss the limitations of the device. The pulse oximeter only gives you a limited amount of information, and is in reality just a snapshot of your functioning at that particular time. For example, it does not tell you the concentration of CO2 (Carbon Dioxide, the waste product of your breathing and something that is not healthy in high levels) in your blood stream. This means that you could be retaining a large amount of CO2, which could be limiting the amount of usable oxygen in your blood.

In other words, the pulse oximeter is not a substitute for more extensive tests that give you and your doctor a better idea of your exact pulmonary function.

The second limitation is that all pulse oximeters “are not equal.” Less expensive units often do not have the accuracy of other more expensive units. It is never a bad idea to take your unit with you to your doctor’s appointment and compare the readings with his unit. I was at a trade show one time and a company there was selling very inexpensive pulse oximeters. I tried 6 different units and never once was able to get a reading! In order to get an accurate oxygen saturation reading, the device must sense every beat of a fairly strong pulse – if your pulse is irregular, weak or not being sensed for some reason, the pulse oximeter may show an oxygen reading, but it is not necessarily accurate. It is also important to keep in mind that many things can affect the reading, such as nail polish, cold or heat, or even which finger you are using it on. If your hands are cold, warm them before taking a reading. If you get a suspicious reading, take it again, or maybe use another finger.

Now for the question of understanding the readings. Ideally, a reading should show a relatively normal heart rate (between 60-100 beats per minute) and an oxygen reading in the middle to high nineties. If the heart rate is higher than usual, but the oxygen number is normal, it means that the heart is working harder to keep your saturations high which could indicate a problem if it remains that way on subsequent readings. If the heart rate is high and the oxygen reading is low, it could also indicate a problem. The important thing is to not panic! Wait a few minutes, and take another reading. If the abnormal readings continue, and you are feeling out of breath, contact your doctor.

To get more information on pulse oximeters, check out our educational materials, which has a lot of good information that can really help you!

Thanks for writing, and be sure to stay in touch!

-The COPD Coach

Coaches Corner is aimed at providing information for individuals with COPD to take to your doctor, and is not in any way intended to be medical advice. If you would like to submit a question to the Coaches Corner email us at [email protected] We would love to hear your questions and comments. You can address your emails to The COPD Coach.


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